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spoons
10-26-2008, 02:39 PM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Impact Blue
10-26-2008, 02:51 PM
Have you been using the same cue for years? during this period.

If so, I would suggest trying another person's cue that is more rear balanced. It's my own personal understanding that your grip hand makes a lot of "comfort" judgements based on this.

For me, a more forward balanced cue does the trick, as I like a ligher-feeling cue. But really in fact it is the same ol' 19oz.

spoons
10-26-2008, 03:01 PM
I actually used to think that was the case, but I've had a handful of cues over the past few years, and always the same result. Even with the countless bar cues that I've used.

For me, it seems to be more about my body positioning than it does about the balance point.

Thanks for the reply, though. I might have to take a closer look into something like that.

mreightball
10-26-2008, 03:07 PM
There are many different pro players that have unorthodox strokes and stances etc. and still shoot excellent so If you can master the way you shoot go at it.
Ron

Texas Prez
10-26-2008, 03:15 PM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

The whole purpose of a perpendicular back arm is to get a pendulum motion that is consistent every time. The reason why this is important is because during your contact point with the cueball, if your back arm is completely perpendicular with the table that means that you cue is contacting the cue ball on a level plane. This just assures a more consistent hit and more predictablility of your stroke. It is worth trying to develop your pendulum motion of your back arm but personally think that if your stroke is solid and consistent then you stoke is solid and consistent!

If it ain't broke...don't fix it (but when it breaks, write a new post! lol)

ShootingArts
10-26-2008, 03:21 PM
Simple mechanical theory using a pendulum stroke indicates that to minimize the up and down motion of your tip when a circular motion(the arc of the pendulum) is converted to linier motion through a fixed point, your bridge, the best place to hit the cue ball is when the pendulum is at the bottom of it's stroke with the least curving arcing motion. (slightly adjusted because the cue is rarely perfectly level and to support this theory the forearm should be at a perfect right angle to the stick when contact is made with the cue ball)

However, that is theory. Having watched strokes of the pro's for years, looked at the pictures and video's of many instructors, and watched many top local players, I note that with rare exceptions all commonly address the cue ball before shooting with the forearm anywhere from slightly to pronouncedly ahead of the "correct" right angle. Obviously the tip goes further forward to contact the cue ball so with the exception of the very few using a slip stroke they are using the same technique you are.

Don't make changes based on theory, take a hard look at what is working for you and for most other people. Does what is happening support the theory? If not toss the theory out the window. For the most perfect pendulum using the right angle contact look at video of Jasmin Ouschan. Bear in mind that she has been coached since she was a small child however, that is anything but a natural stroke in my opinion. Definitely effective but so are dozens of other strokes.

Hu


Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Texas Prez
10-26-2008, 03:33 PM
Jasmin Ouschan definately has the best technical stroke that I have seen. I mean it does look a little unnatural but that it because it is a focal point of her game; especially during high pressure situations such as televised matches like the ones we usually see. But honestly....that girl is GOOD! :)

grindz
10-26-2008, 03:38 PM
:wink:

Other factors for you may be ...the size of the handle where it feels comfortable to your hand (different makers have varying diameters)...the goal is trying to have as long of a straight line for the shaft in the contact zone (where the most consistent hit is the one going through the ball toward the target as long as possible to maximize your chances of spot on accuracy, with the possible exception of different spins).....the length of space between your bridge hand and contact point will also factor in.

Lots of different points of interest, but if it concerns you it may be that you need a narrower handle for your hand to feel comfortable (or a looser grip) so you can slide it back. All things that this banger wouldn't know!!

Good luck.

td

Cameron Smith
10-26-2008, 03:46 PM
I believe it also has to do with the timing of your stroke as well.

If your arm is perpendicular at contact it's easier to hit the cue ball at peak accelaration. However if your lower arm is too far forward you may be de-accelarating at contact.

Even if you are stroking straight, that doesn't mean your stroke is perfect. By improving your timing you can generate more power and spin with less effort.

ShootingArts
10-26-2008, 03:53 PM
One thing the theory doesn't consider is that there are several more motion points beyond the elbow. The wrist is in motion and can be used to extend or move the theoretical ideal angle of the fore arm. The fingers can be used for the same result.

Simple answers work for machines. Simple answers can work for humans too but since we are far more complicated and sophisticated than any machine ever made there are often other solutions also. A pure pendulum feels too mechanical to me and I can't get comfortable with it. Slightly modified works much better and on bar tables or for close work I may go to almost a pump stroke.

Watching the greats of the fifties and sixties I notice individual players using various strokes for various shots, they didn't try to make one stroke fit all shots. With the same equipment and same competition to hone themselves against as today's players I think they would do just fine today.

Hu


:wink:

Other factors for you may be ...the size of the handle where it feels comfortable to your hand (different makers have varying diameters)...the goal is trying to have as long of a straight line for the shaft in the contact zone (where the most consistent hit is the one going through the ball toward the target as long as possible to maximize your chances of spot on accuracy, with the possible exception of different spins).....the length of space between your bridge hand and contact point will also factor in.

Lots of different points of interest, but if it concerns you it may be that you need a narrower handle for your hand to feel comfortable (or a looser grip) so you can slide it back. All things that this banger wouldn't know!!

Good luck.

td

"T"
10-26-2008, 05:31 PM
What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Not a teacher, but I believe the geometry of the reason is partially to keep the high vs low contact with the cueball more consistent.

Maybe if one of the things you are struggling with is cueball distance control, especially when drawing, the maybe the back arm being forward leaves too small a margin of error to be consistent.

Then again, if you're rock solid with touch and able to draw whitey back on top of a dime from any distance, forget about it. :D

BRKNRUN
10-26-2008, 05:54 PM
The geometry has already been explained...If you are past perp...at impact that mean your grip is going up and the tip is going down.....

If you are far enough Away from the CB this may mean you need to drop your elbow to maintain the tip accuracy...(Probably not good)

However....If you really look close at many top players....You will see that they "set up" with the arm in a pependicuar position, but at impact they are "just forward" of perpendicular....I watched Jasmin and she is "Just Forward" ..(at impact)

The reason for this is that if you set up perpendicular...the tip is just short of the CB so at impact your arm will end up "Just Forward"...

I see MANY top pros that are "Just Forward"...I set up this way and I am sure I am also just forward at impact.

The key "I guess" is to make it a consistent set up and I try and get my tip as close to the CB on set up as possible to minimze the "just forward: aspect.

I personally can't get to perpendicular "at impact" because I can't get comfortable setting up with my hand just behind perpendicular...I feel it is much more consistent and natural to "set up" perpendicular

JimS
10-26-2008, 06:03 PM
Do a video and see if the cue is reasonably level at contact. If it is then you must be compensating elsewhere. If the arm is past level the cue tip should be traveling upwards at contact.... unless the wrist or hand is keeping it level.

What the hell... if the cue is level at contact seems like all is well.

Snapshot9
10-26-2008, 06:14 PM
with your grip hand forward, you are pushing the cueball not stroking it.
Players, insecure with their stroke, do this trying to guide or control the cueball more. It is called overcompensation.

Bet I could watch you shoot and tell you what shots that are a problem for you.

crosseyedjoe
10-26-2008, 06:20 PM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Keeping your arm perpendicular is good for faster learning curve, but I think the right or left sway is something that affects your stroke accuracy more dramatically.

fd_colorado
10-26-2008, 06:49 PM
The simple answer is...

If you contact the ball past the perpendicular, you WILL drop your elbow (a generally agreed on bad thing...right up there with jumping up).

Colin Colenso
10-26-2008, 07:20 PM
What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!
I think the benefits are minimal, unless you are extremely far forward in which case you may be cramping your stroke.

Many of the world's best shooters drop their elbow on some shots. I wouldn't sweat it if you can hit the CB where you want to.

Hardest thing is getting the bridge on the right line for the shot and then not swooping sideways. If you can do that it's hardly gonna matter if your back arm is perpendicular.

btw: There's also the argument that the back arm should be vertical (looking from the front) to allow straight pendulum cuing. Again, very few pros are perfectly vertical in this plane, but most have learned to move the cue straight enough so as to get the desired effect. I spent years trying to get my arm vertical in this plane. It was largely a waste of time. I would have gotten 10 times the benefit from paying attention to where I was placing my bridge hand I believe. I mean, place your bridge hand slightly off the required alignment and you're not gonna make that pot without some sideway swooping or bridge hand movement.

Colin

softshot
10-26-2008, 11:41 PM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!


my guess would be that you are changing your grip position but not changing anything else..

your grip has developed into what it is by compensating for your bridge and your tip to cueball warm up distance the farther away you are... you bring into play a whole battery of things..

if you find the bridge distance that works with a perpendicular grip arm and a level cue.. and you begin the stroke with the tip at the ball... if your elbow is the only joint moving.. and you have a nice loose grip...you have a 100% chance of hitting the cueball exactly where you intend to....

you need all the fundamentals not just one...

you are obviously not happy with the level of your game as it is or you wouldn't be looking for help...

SPF... it works... find an instructor and fix it once and for all..

good luck..

pdcue
10-27-2008, 02:47 AM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Don't change.

The perpendicular at contact is a popular method - but not the only method, used by top players.

Both Willie Mosconi and Luther Lasiter, held the cue so far foward
that they had their arm perpendicular at the end of their backswing.

If you have 'plenty' of stroke. lord knows they did, playing the way
you do, there is no benifit to changing now.

Dale<sometimes forward holder>

pdcue
10-27-2008, 02:57 AM
The simple answer is...

If you contact the ball past the perpendicular, you WILL drop your elbow (a generally agreed on bad thing...right up there with jumping up).

Not agreed on by most every top Straight Pool player
of the past 80 years.

Watch a few videos of them hitting break shots.

Dale

Patrick Johnson
10-27-2008, 06:23 AM
Simple mechanical theory using a pendulum stroke indicates that to minimize the up and down motion of your tip when a circular motion(the arc of the pendulum) is converted to linier motion through a fixed point, your bridge, the best place to hit the cue ball is when the pendulum is at the bottom of it's stroke with the least curving arcing motion. (slightly adjusted because the cue is rarely perfectly level and to support this theory the forearm should be at a perfect right angle to the stick when contact is made with the cue ball)

However, that is theory. Having watched strokes of the pro's for years, looked at the pictures and video's of many instructors, and watched many top local players, I note that with rare exceptions all commonly address the cue ball before shooting with the forearm anywhere from slightly to pronouncedly ahead of the "correct" right angle. Obviously the tip goes further forward to contact the cue ball so with the exception of the very few using a slip stroke they are using the same technique you are.

I think maybe the reason so many hit a little forward of perpendicular is that they can feel that's where their acceleration peaks. I think hitting the CB at the point where your acceleration peaks does two things: gives the most action for the effort and gives the best feel for speed control.

I've always heard that the stroke begins to "coast" when the forearm reaches perpendicular, but I've never quite believed it - the arm's physiology doesn't seem to me to dictate that.

I don't know any of this "scientifically"; just my impressions.

pj
chgo

ShootingArts
10-27-2008, 07:46 AM
Some players have their wrists bent back, John Schmidt is one example I believe, so the grip to elbow line is still close to a right angle to the cue stick although the fore arm is a bit further ahead. However when you mention feel it makes me think of something else. With the arm bent slightly more forward it absorbs the impact with the cue ball a little better and the strike feels a little more comfortable. Not that the impact is a major issue but I wonder if we don't subconsciously seek to minimize it? Purest speculation on my part also, I have no idea why the position seems most natural.

Speed control is a very good point. Mine suffers if I hit the cue ball early with my forearm before perpendicular and isn't the best if I strive for a perfect pendulum and right angle between the cue and fore arm at impact. My best speed control is hitting the cue ball slightly late. When I set up to hit the cue ball with my fore arm at a perfect right angle my arm still feels cocked when I stop at the cue ball on my practice strokes and in the set position too. These are individual things for me and I don't know if they apply to other people.

I just had a thought that led me to step in front of my bathroom mirror. When I turn sideways bend over into a pool stance and move my upper arm into position letting my fore arm dangle I find that due to muscle tension my fore arm actually angles forward several inches when completely relaxed. It seems my true muscular neutral position isn't with my fore arm straight down but with it a few inches ahead of vertical. This is identical or very close to where I choose to hit the cue ball. I have to give this more thought but it may be the key.

Hu


I think maybe the reason so many hit a little forward of perpendicular is that they can feel that's where their acceleration peaks. I think hitting the CB at the point where your acceleration peaks does two things: gives the most action for the effort and gives the best feel for speed control.

I've always heard that the stroke begins to "coast" when the forearm reaches perpendicular, but I've never quite believed it - the arm's physiology doesn't seem to me to dictate that.

I don't know any of this "scientifically"; just my impressions.

pj
chgo

JoeyInCali
10-27-2008, 08:11 AM
Not agreed on by most every top Straight Pool player
of the past 80 years.

Watch a few videos of them hitting break shots.

Dale
Stroke slippers?
A lot of them let that cue go.

pdcue
10-27-2008, 12:36 PM
Stroke slippers?
A lot of them let that cue go.

No, it isn't a slipstroke. It is simply a smooth, controlled, follow-thru.
Steve Mez would often end the stroke with his elbow all the way down
by his waist.<when he still had one>

Dale

spoons
10-27-2008, 01:03 PM
Thanks for the thoughtful replies everyone, there are some great tidbits in here.

I've long been a proponent of the importance of predictable results over raw ability, but obviously if I could combine the two, I'd like to do that.

I'm not sure what I'll do in the end, but I appreciate the perspectives of folks on here.

I think if there's one thing that would push me over the edge, it would be somehow knowing that I could achieve the same results with less effort. From what I'm reading here, it sounds like making contact peak acceleration is generally regarded as more important than the actual position along the pendulum swing. Right?

crosseyedjoe
10-27-2008, 01:36 PM
Thanks for the thoughtful replies everyone, there are some great tidbits in here.

I've long been a proponent of the importance of predictable results over raw ability, but obviously if I could combine the two, I'd like to do that.

I'm not sure what I'll do in the end, but I appreciate the perspectives of folks on here.

I think if there's one thing that would push me over the edge, it would be somehow knowing that I could achieve the same results with less effort. From what I'm reading here, it sounds like making contact peak acceleration is generally regarded as more important than the actual position along the pendulum swing. Right?

Don't watch Mike Davis and Bustamante or you might think you are stupid for following instructional advice. :D

Siz
10-27-2008, 02:15 PM
I wouldn't worry at all about cueing a little forward of perpendicular. It is behind perpendicular that is a real no-no IMO

Bob Jewett
10-27-2008, 02:37 PM
... If your arm is perpendicular at contact it's easier to hit the cue ball at peak acceleration. ...
A small technical nit.... It's peak velocity you want, not peak acceleration. Velocity and acceleration are very different in physics, but many people confuse the two. If you hit at peak velocity, you have the most efficient and powerful stroke and likely the most consistent, as well.

spoons
10-27-2008, 02:43 PM
Hi Bob. In a typical stroke, where would those two points fall? Or is that too loaded a question to answer in the context of this thread?

Bob Jewett
10-27-2008, 02:51 PM
Hi Bob. In a typical stroke, where would those two points fall? Or is that too loaded a question to answer in the context of this thread?
The technical answer is pretty simple. For a typical stroke, the peak acceleration occurs at a time when the stick has about half its peak velocity. At peak velocity, there is zero acceleration. Those two statements are very basic physics, and hopefully no one will attempt to argue with them.

spoons
10-27-2008, 03:02 PM
The technical answer is pretty simple. For a typical stroke, the peak acceleration occurs at a time when the stick has about half its peak velocity. At peak velocity, there is zero acceleration. Those two statements are very basic physics, and hopefully no one will attempt to argue with them.


Thanks. That makes sense to me.

ShootingArts
10-27-2008, 04:52 PM
The technical answer is pretty simple. For a typical stroke, the peak acceleration occurs at a time when the stick has about half its peak velocity. At peak velocity, there is zero acceleration. Those two statements are very basic physics, and hopefully no one will attempt to argue with them.


Bob,

I definitely wouldn't argue with anyone saying acceleration has ended at peak velocity and I don't know enough to debate where peak acceleration would be during muscle contraction. I think the real questions were where would your fore arm be at peak acceleration and peak velocity. I may be mistaken but I think we are actually only interested in peak velocity. Any idea where this is reached in terms of the angle of the fore arm? Even a general range would be helpful.

Hu

crosseyedjoe
10-27-2008, 05:25 PM
nothing . . .

crosseyedjoe
10-27-2008, 05:32 PM
The technical answer is pretty simple. For a typical stroke, the peak acceleration occurs at a time when the stick has about half its peak velocity. At peak velocity, there is zero acceleration. Those two statements are very basic physics, and hopefully no one will attempt to argue with them.

No argument, if you're not talking about imparting the most power/force.

Bob Jewett
10-27-2008, 06:25 PM
No argument, if you're not talking about imparting the most power/force.
But I am. You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.

Bob Jewett
10-27-2008, 06:32 PM
... I think the real questions were where would your fore arm be at peak acceleration and peak velocity. ...
Well, judging from how a lot of players are now choking up on the stick for break shots, I'm suspecting that maximum velocity happens somewhat after bottom dead center for those shots, but of course they are not exactly standard shots. I think that if you are looking for the best body position for maximum power, you need to get a sports motion professional involved. I don't know of any such study.

For the usual range of shots, I think you are not looking for maximum power; you are looking for consistency. On most shots, I can hit the ball much harder than I should.

alstl
10-27-2008, 07:47 PM
The delivery of a pool cue reminds me of the old battering rams.

http://www.pbs.org/wgbh/nova/lostempires/trebuchet/images/batteringram.gif

They would swing the battering ram back and when it was hanging perpendicular and parallel to the ground it would make impact, thus delivering maximum force.

Maybe it's just a coincidence but see a similarity.

Patrick Johnson
10-27-2008, 08:12 PM
For the usual range of shots, I think you are not looking for maximum power; you are looking for consistency.

This topic is full of confusing terminology - acceleration, velocity, power - all with different meanings. So to clarify:

You get maximum stroke efficienty and consistency by hitting at peak velocity, and peak velocity occurs in every shot, soft or hard (it's not synonymous with maximum power). So even though on most shots you're not looking for maximum power, you are looking to hit the CB at peak velocity.

We're not sure whether peak velocity occurs right at perpendicular or a little forward of that, but we know it's somewhere around there and we also know that's where the tip is traveling with the least up-and-down variation. So there's a lot to say for hitting the CB at or maybe just a little forward of the perpendicular position.

pj
chgo

ShootingArts
10-27-2008, 08:21 PM
Well, judging from how a lot of players are now choking up on the stick for break shots, I'm suspecting that maximum velocity happens somewhat after bottom dead center for those shots, but of course they are not exactly standard shots. I think that if you are looking for the best body position for maximum power, you need to get a sports motion professional involved. I don't know of any such study.

For the usual range of shots, I think you are not looking for maximum power; you are looking for consistency. On most shots, I can hit the ball much harder than I should.


Bob,

I think you answered the question, I'd need to talk to a sports motion professional. What I was looking for was the maximum velocity for a given amount of effort. There is no question that we can almost always apply more power and speed than we need but where in the stroke do we get maximum velocity for minimum effort? Maybe the area from 98% velocity through peak velocity and back to 98% velocity.

Noting the true neutral position of my fore arm when I let it dangle freely earlier I suspect that this peak velocity area is a little forward of where I would have guessed looking at a purely mechanical model controlled by gravity. Standing with my arms hanging fully relaxed muscle tension keeps my arms hooked maybe ten degrees at the elbow. Just on a WAG, I'd think that my area of peak velocity on a soft to medium stroke might be from straight down to twenty degrees forward. In other words, centered around my arm's neutral position rather than the theoretical position indicated by a mechanical model and gravity. This agrees with your observations of break shots.

Just speculation on my part, as you say there are folks that specialize in this field and tune athletes to be their best. Doubt I could afford one's services to answer a question of only minor interest as I don't think it is the primary concern in developing a stroke. It would be a consideration, but not the major consideration.

Thanks for your answer,
Hu

crosseyedjoe
10-27-2008, 08:22 PM
The delivery of a pool cue reminds me of the old battering rams.

http://www.pbs.org/wgbh/nova/lostempires/trebuchet/images/batteringram.gif

They would swing the battering ram back and when it was hanging perpendicular and parallel to the ground it would make impact, thus delivering maximum force.

Maybe it's just a coincidence but see a similarity.

Yes, if you can make your arm a free swinging pendulum. It's not. You are using muscle contraction to mimic the pendulum movement.

crosseyedjoe
10-27-2008, 09:08 PM
But I am. You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.

1. and how do you reach faster velocity when distance is constant?
2. what do you mean by cue stick peak velocity after peak acceleration? are you saying that you can can go faster when the acceleration is now being affected by the retarding force of your muscle?

softshot
10-28-2008, 01:55 AM
We know peak acceleration occurs at the middle of the stroke...

we know that a level cue at the cueball delivers the most accurate impact.

if we force the middle of the stroke to occur at the cueball with a level cue.... (the Set position)

as long as your grip or your shoulder do not alter the path of the cue..

your grip position at impact should be perpendicular.. the middle of the stroke..

peak acceleration plus peak accuracy... equals the right way to do it..

JMO

softshot
10-28-2008, 02:42 AM
But I am. You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.


you will probably blow me out of the water with a bunch of math here but...

given these two choices..

would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall????

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed..

human muscles can control acceleration much better that they can control velocity.. from what I have read..

Fatboy
10-28-2008, 02:52 AM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

it took me way too long to get that perpendicular spot at the point of contact, I did and by the time I got it I was a better player-perhaps because it took so long, years later I have watched a zillion players and came to one conclusion-its over rated, Lassiter was WAY choked up on his cue, Davenport was perhaps the closest to 90 degrees as anyone, and I have seen less champions that are open more than 90 degrees,

having said all that, I think its better to be 90 or under, open greater than 90 degree strokes look funny and limited in some ways.

Patrick Johnson
10-28-2008, 09:46 AM
Bob Jewett:
The acceleration at the instant of impact in not significant.

softshot:
you will probably blow me out of the water with a bunch of math here but...

given these two choices..

would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall????

No math necessary. Since they're both going the same speed at impact, the effect of the collision is exactly the same. Whether they get to that speed by speeding up or slowing down (or coasting) is irrelevant.

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed...

Acceleration doesn't "impart momentum" that's unrelated to speed, and it doesn't matter to the amount of force at a given speed.

human muscles can control acceleration much better that they can control velocity.. from what I have read...

I don't know what that means.

pj
chgo

Patrick Johnson
10-28-2008, 09:56 AM
peak acceleration plus peak accuracy... equals the right way to do it..

I think this should be "peak velocity plus peak accuracy".

Think of driving a car. As long as your foot is pressing the accelerator (gas pedal), the car is accelerating*. You can back off on the gas a little so you're accelerating less, but still accelerating some and still gaining speed (velocity). So peak acceleration can occur before peak velocity - but peak velocity is where you get the most consistency.

pj
chgo

*P.S. Technically, "acceleration" means any time your speed is changing, either speeding up or slowing down. Taking your foot off the gas, or even hitting the brakes, is "accelerating" in technical terms. But for this discussion I think that just confuses things, so I'm using the word "accelerate" the way non-technical people use it: to mean speeding up only.

Cornerman
10-28-2008, 10:02 AM
We know peak acceleration occurs at the middle of the stroke...

we know that a level cue at the cueball delivers the most accurate impact.

if we force the middle of the stroke to occur at the cueball with a level cue.... (the Set position)

as long as your grip or your shoulder do not alter the path of the cue..

your grip position at impact should be perpendicular.. the middle of the stroke..

peak acceleration plus peak accuracy... equals the right way to do it..

JMOUmmm.... No.

I think you're confusing acceleration with velocity.

I think peak acceleration (linear acceleration, horizontal to the cueball) is when the hand is about 45 degrees short of perpendicular (wrt horizontal). Peak velocity is when the hand is at perpendicular.

The velocity just before and just after perpendicular is almost the same. So, hitting around perpendicualar is "right" from a constant/consistency point of view. A few degrees from perpendicular still gets you about the same speed. And at perpendicular, you should be at about zero acceleration as others have said.

A good case can be made that says that many (most?) top players are actually decelerating their cues just prior to impact with the cueball. That's okay since it's the velocity that matters, not the acceleration (which is nearly zero at impact anyway).

Fred

Cornerman
10-28-2008, 10:19 AM
would you rather be on the motorcycle that accelerated to 55 MPH before impact with the wall.???

or the driver of the bike that just barely slowed down to 55 MPH at impact with the wall???? Same impact.

acceleration matters... and acceleration imparts momentum which imparts a consistent force that is unrelated to speed.. Acceleration doesn't impart momentum. Speed does.

human muscles can control acceleration much better that they can control velocity.. from what I have read..Why would you think that? Even if this was true, what exactly would it matter? Acceleration at impact doesn't mean anything. Velocity does.

Look, if you are standing on a table, you're accelerating towards the earth at gravitational acceleration, even if you're actually not moving. If the table is only 4 feet high, and you jump off, you're not accelerating any more than gravitational acceleration, but your velocity starts to increase. You'll land on the floor with no problem, because you haven't accelerated to any significant speed.

Take the same situation but jump off a 40' building. Do you understand that you'll be accelerating the same regardless of how high you started (terminal velocity and wind resistance dismissed, of course)? But, when you hit the ground, you will have accelerated to a tremendously significant speed. And you'll get pancaked. So, the fact that all three cases the acceleration is exactly the same means nothing. The velocity at impact does.

I hope that sheds more light into the terminologies.

Fred

Bob Jewett
10-28-2008, 11:00 AM
1. and how do you reach faster velocity when distance is constant?
2. what do you mean by cue stick peak velocity after peak acceleration? are you saying that you can can go faster when the acceleration is now being affected by the retarding force of your muscle?
If the distance over which you are accelerating is constant, and assuming your arm can provide uniform maximum force over that distance, but cannot go instantaneously from no force to maximum force, then the technique to get to maximum stick speed at impact would be to backstroke as quickly as possible, don't have any pause at the end of the back stroke, and have the full maximum force applied from somewhat before the backstroke stops until contact with the cue ball. But I don't think arms work that way, and I don't think that would be a good technique for any shot but a power break.

As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

crosseyedjoe
10-28-2008, 11:14 AM
As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

True, only if there in no retarding force associated along the plane of action.

As for question 2, a definition may help: Acceleration is by definition the rate of change of velocity. If there is (positive) acceleration, the velocity is increasing. If the stick is still accelerating, and you wait a little while, the stick will be going faster, by the definition of acceleration. Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.

What mechanical system is this?

Bob Jewett
10-28-2008, 11:51 AM
... What mechanical system is this?
My statement was based simply on the definitions of acceleration and velocity. Those definitions apply to all mechanical systems. I looked briefly for some tutorials on the web, and you can find several using the words "velocity acceleration definition" with various levels of technical detail. Here is one with some helpful diagrams:
http://hep.physics.indiana.edu/~rickv/More_Kinematics.html

alstl
10-28-2008, 12:17 PM
Yes, if you can make your arm a free swinging pendulum. It's not. You are using muscle contraction to mimic the pendulum movement.

Exactly.

..........

Patrick Johnson
10-28-2008, 01:38 PM
...if you are standing on a table, you're accelerating towards the earth at gravitational acceleration, even if you're actually not moving.

A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo

Cornerman
10-28-2008, 01:45 PM
A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo
Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.


Fred

Bob Jewett
10-28-2008, 02:04 PM
Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.


Fred
If you base acceleration on net force, which is usually done, then the opposing forces cancel and you have zero net acceleration.

Cornerman
10-28-2008, 02:31 PM
If you base acceleration on net force, which is usually done, then the opposing forces cancel and you have zero net acceleration.
Well of course. But you'd have a hell of a time trying to calculate that opposing force if you denied yourself the use of an acceleration term. If you do deny yourself this, please don't design any bridges for me.

The gist of my post was that the word acceleration wasn't what defined the impact that's being discussed. Summing up individual forces is okay given this context.

Fred

Patrick Johnson
10-28-2008, 03:57 PM
A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

Well.... your body still must have an acceleration vector towards the earth or else you'd have no weight force. The table just happens to be opposing it.

Oh, I see what you're saying. I'll defer to you and Bob on vectors.

pj
chgo

crosseyedjoe
10-28-2008, 04:54 PM
I think this should be "peak velocity plus peak accuracy".

Think of driving a car. As long as your foot is pressing the accelerator (gas pedal), the car is accelerating*. You can back off on the gas a little so you're accelerating less, but still accelerating some and still gaining speed (velocity). So peak acceleration can occur before peak velocity - but peak velocity is where you get the most consistency.

pj
chgo
"peak velocity plus peak accuracy" - no argument on that one.

As for the car;
1. It's possible because it involves a wheel system.
2. Letting off on the gas a little is not a retarding force.

crosseyedjoe
10-28-2008, 05:01 PM
My statement was based simply on the definitions of acceleration and velocity. Those definitions apply to all mechanical systems. I looked briefly for some tutorials on the web, and you can find several using the words "velocity acceleration definition" with various levels of technical detail. Here is one with some helpful diagrams:
http://hep.physics.indiana.edu/~rickv/More_Kinematics.html

This one does not apply to all mechanical system: "Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero."

What you are suggesting mostly concerns classical pendulum mechanical system in which the acceleration acts vertically and the acceleration goes to zero once the pendulum reaches the bottom(at peak velocity) because its direction is now tangent to the direction of the acceleration.

Stroke is not a pendulum system.

crosseyedjoe
10-28-2008, 05:35 PM
A nit: acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

pj
chgo

PJ, remember the third law of motion, opposite and equal reaction. You always have an acceleration component even when standing still. It's just that the forces are cancelling out which shouldn't be confused with acceleration cancelling out. That's why you will weigh less on the surface of the moon.

dr_dave
10-28-2008, 06:32 PM
You get the highest cue ball speed with the fastest stick speed. The acceleration at the instant of impact in not significant. This has been discussed extensively before, and you may want to look over Dr. Dave's recent articles on this for the details.Bob,

I don't have any recent articles on this, but I did discuss it some in the stroke analysis video we shot together. Here it is:

HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett (http://billiards.colostate.edu/high_speed_videos/new/HSVB-40.htm)

Regards,
Dave

crosseyedjoe
10-28-2008, 07:21 PM
Bob,

I don't have any recent articles on this, but I did discuss it some in the stroke analysis video we shot together. Here it is:

HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett (http://billiards.colostate.edu/high_speed_videos/new/HSVB-40.htm)

Regards,
Dave

And did I mention the most power? :D

Patrick Johnson
10-28-2008, 07:22 PM
Me:
... acceleration means a change in velocity (which wouldn't happen until you step off the table), but I agree with everything else.

crosseyedjoe:
PJ, remember the third law of motion, opposite and equal reaction. You always have an acceleration component even when standing still. It's just that the forces are cancelling out which shouldn't be confused with acceleration cancelling out. That's why you will weigh less on the surface of the moon.

Yes, I'm familiar with that law, and with the opposing forces that keep us stuck to the Earth without sinking into it. But I don't think that defines acceleration (or is why we weigh less on the moon, which is simply because the moon has less mass and gravity than Earth). It has to do with force, and I think acceleration is a potential product of force that isn't always realized.

I think Fred's comment about vector may also be about force rather than acceleration, but I don't know enough about it to say that for sure.

Here's how the website Bob linked to (Indiana University Physics Department) defines acceleration:

"acceleration is defined as the ratio of change in velocity to the time interval over which the change occurs"

I think this means that acceleration is zero for things at rest, but I'm willing to accept on faith that acceleration means something even for things at rest, especially since it's a sidebar discussion in this thread. We've already learned that peak velocity, not peak acceleration, is the important part of a stroke.

pj
chgo

crosseyedjoe
10-28-2008, 07:34 PM
Yes, I'm familiar with that law, but I don't think it has anything to do with the definition of acceleration (or why we weigh less on the moon). It has to do with force, of which acceleration is a potential product.
pj
chgo

F=ma; your mass is contant, what does change to have a lesser weight on the moon? Interestingly enough as long as there is a push or pull there is acceleration.

. . .We've already learned that peak velocity, not peak acceleration, is the important part of a stroke.

pj
chgo

No argument on that. Sorry, I'm just being testy about achieving the most powerful contact which is to not ever let go of acceleration until contact.

softshot
10-28-2008, 10:41 PM
human muscles can control acceleration much better that they can control velocity.. from what I have read..


I don't know what that means.

pj
chgo

I concede the momentum argument..

contraction in a muscle cell is shrinking and accelerating towards it's center until its mass forces it to stop. that's how a muscle works.. peak acceleration occurs at the middle of the stroke at BDC (bottom dead center) and that point should be impact in a fundamentally correct stroke.

velocity is irrelevant.. I stroke at several different velocity's.. and I do so through controlling acceleration...the contraction of my muscles ( accelerating towards center until stopped by its own mass)

you transfer peak acceleration to your stick because now the stick has forces working on it as well.. the stick has reached the peak velocity you can impart to it... with a loose grip... and that transfer occurs at peak acceleration

BDC... the set position.. that is the point where the biology and physics meet at peak efficiency.. i.e... the right way to do it..

I don't care what the peak velocity of my cue is... I care about how much of that velocity is under my control.. and all a muscle can do is accelerate twards its own center. all I can control is my muscle.. I control acceleration.. not velocity..

softshot
10-28-2008, 11:31 PM
theoretically if a muscle was strong enough you could create a black hole in your own bicep..... all you need to do is reach an acceleration that the mass cannot stop...


let the physics guys chew on that one for a while LOL :thumbup:

ShootingArts
10-29-2008, 06:03 AM
Muscle acceleration is tricky because it is under our control if we work at it. My normal tendency is to want to get up to the speed I want to hit the cue ball quickly and basically maintain that speed. However when I work on starting my forward stroke slowly and increasing that speed much more gradually I seem to miss fewer shots. One of the things I need to practice and do practice now and then. I think it should be an ingrained part of my game but it isn't yet.

Hu


I concede the momentum argument..

contraction in a muscle cell is shrinking and accelerating towards it's center until its mass forces it to stop. that's how a muscle works.. peak acceleration occurs at the middle of the stroke at BDC (bottom dead center) and that point should be impact in a fundamentally correct stroke.

velocity is irrelevant.. I stroke at several different velocity's.. and I do so through controlling acceleration...the contraction of my muscles ( accelerating towards center until stopped by its own mass)

you transfer peak acceleration to your stick because now the stick has forces working on it as well.. the stick has reached the peak velocity you can impart to it... with a loose grip... and that transfer occurs at peak acceleration

BDC... the set position.. that is the point where the biology and physics meet at peak efficiency.. i.e... the right way to do it..

I don't care what the peak velocity of my cue is... I care about how much of that velocity is under my control.. and all a muscle can do is accelerate twards its own center. all I can control is my muscle.. I control acceleration.. not velocity..

JimS
10-29-2008, 06:32 AM
Muscle acceleration is tricky because it is under our control if we work at it. My normal tendency is to want to get up to the speed I want to hit the cue ball quickly and basically maintain that speed. However when I work on starting my forward stroke slowly and increasing that speed much more gradually I seem to miss fewer shots. One of the things I need to practice and do practice now and then. I think it should be an ingrained part of my game but it isn't yet.

Hu

I think that's what a smooooooth stroke is about. Even the power stroke... it's longer so it can pick up speed gradually.

By the way.... back arm perpendicular to ???? to what??? The cue?? The floor?? Thanks, Jim

jsp
10-29-2008, 06:33 AM
This one does not apply to all mechanical system: "Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero."

What you are suggesting mostly concerns classical pendulum mechanical system in which the acceleration acts vertically and the acceleration goes to zero once the pendulum reaches the bottom(at peak velocity) because its direction is now tangent to the direction of the acceleration.
Actually, it does apply to all real mechanical systems. The assumption of course is that the acceleration doesn't stay positive indefinitely, but eventually reaches zero at some time.

If acceleration never reaches zero, then it's obvious that the velocity is forever increasing and the peak velocity is whatever it is at the present moment.

jsp
10-29-2008, 06:50 AM
Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero.
Oh, and just to clarify, the above statement is only true if acceleration doesn't go negative at any prior point. Think of velocity as the integration of the acceleration curve over time.

Scott Lee
10-29-2008, 07:14 AM
JimS...Almost always perpendicular to the cuestick!

Scott Lee
www.poolknowledge.com

By the way.... back arm perpendicular to ???? to what??? The cue?? The floor?? Thanks, Jim

ShootingArts
10-29-2008, 07:23 AM
I think that's what a smooooooth stroke is about. Even the power stroke... it's longer so it can pick up speed gradually.

By the way.... back arm perpendicular to ???? to what??? The cue?? The floor?? Thanks, Jim

Jim,

Back arm perpendicular to the cue in my opinion as much as possible. That isn't how I shoot but it is definitely a good starting point. Watching old video and looking at images of people who advocated a "level cue" they often had the rear of the cue elevated three or four inches when there was nothing about the table or balls that demanded it. Obviously, "level" didn't mean taken to extremes for them. when you raise the cue butt, then it would seem that to hit with the fore arm perpendicular to the cue means you will be hitting it a little bit early in relationship to the floor.

"Perfect" mechanics feel very unnatural to me, I suspect because I have a fair amount of natural crook in my elbow, my hands naturally hang in front of my legs when standing. Hitting the cue ball late compared to the theoretical perfect place from a purely mechanical standpoint feels much more natural for me. I don't recommend carrying anything to extremes but I also don't believe in cookie cutter one size fits all either.

Hu

Patrick Johnson
10-29-2008, 07:58 AM
your mass is contant, what does change to have a lesser weight on the moon?

The Moon's mass is less than the Earth's and so it exerts less attractive force. The difference has nothing to do with opposing force.

pj
chgo

JimS
10-29-2008, 08:12 AM
Jim,

Back arm perpendicular to the cue in my opinion as much as possible. That isn't how I shoot but it is definitely a good starting point. Watching old video and looking at images of people who advocated a "level cue" they often had the rear of the cue elevated three or four inches when there was nothing about the table or balls that demanded it. Obviously, "level" didn't mean taken to extremes for them. when you raise the cue butt, then it would seem that to hit with the fore arm perpendicular to the cue means you will be hitting it a little bit early in relationship to the floor.

"Perfect" mechanics feel very unnatural to me, I suspect because I have a fair amount of natural crook in my elbow, my hands naturally hang in front of my legs when standing. Hitting the cue ball late compared to the theoretical perfect place from a purely mechanical standpoint feels much more natural for me. I don't recommend carrying anything to extremes but I also don't believe in cookie cutter one size fits all either.

Hu

Thanks Scott and Hu... that's what I figured but needed clarification in a moment of doubt.

dr_dave
10-29-2008, 09:57 AM
The Moon's mass is less than the Earth's and so it exerts less attractive force.I didn't follow this whole planetary debate here, but the gravitational force between the earth and moon is exactly equal and opposite on both bodies. The force has a greater effect on the moon due to its smaller mass, but the force is the same.

Regards,
Dave

Bob Jewett
10-29-2008, 11:02 AM
This one does not apply to all mechanical system: "Also by the definition of acceleration, peak velocity is achieved exactly when the acceleration is zero." ... Stroke is not a pendulum system.
I think you are not familiar with the standard definitions used in physics. One standard definition is that velocity of an object is the time integral of the net acceleration of the object. This applies to cue sticks and pretty much everything else in the universe. If you feel it does not, please explain why.

crosseyedjoe
10-29-2008, 11:05 AM
The Moon's mass is less than the Earth's and so it exerts less attractive force. The difference has nothing to do with opposing force.

pj
chgo

Ah, how is that attractive force normally referred to and what does it imply?

The system YOU and EARTH, has a net zero acceleration. But when you isolate the body YOU and treat it as a separate system, YOU is accelerating by 9.8m/s^2. I was just hoping for people to use terms and the associated system consistently most specially the modifier NET.

crosseyedjoe
10-29-2008, 11:40 AM
I concede the momentum argument..

contraction in a muscle cell is shrinking and accelerating towards it's center until its mass forces it to stop. that's how a muscle works.. peak acceleration occurs at the middle of the stroke at BDC (bottom dead center) and that point should be impact in a fundamentally correct stroke.

velocity is irrelevant.. I stroke at several different velocity's.. and I do so through controlling acceleration...the contraction of my muscles ( accelerating towards center until stopped by its own mass)

you transfer peak acceleration to your stick because now the stick has forces working on it as well.. the stick has reached the peak velocity you can impart to it... with a loose grip... and that transfer occurs at peak acceleration

BDC... the set position.. that is the point where the biology and physics meet at peak efficiency.. i.e... the right way to do it..

I don't care what the peak velocity of my cue is... I care about how much of that velocity is under my control.. and all a muscle can do is accelerate twards its own center. all I can control is my muscle.. I control acceleration.. not velocity..

Good job. A+

Bob Jewett
10-29-2008, 11:50 AM
... velocity is irrelevant.. ...
This is true only if you don't care how fast the cue ball moves. The speed of the cue ball will be directly proportional to the speed of the stick at the moment of tip-to-ball contact.

And to the extent that you control the acceleration of the stick you control its velocity to the same extent.

Patrick Johnson
10-29-2008, 11:57 AM
...the gravitational force between the earth and moon is exactly equal and opposite on both bodies. The force has a greater effect on the moon due to its smaller mass, but the force is the same.

You're talking about the total combined gravitational force of the two bodies. I'm talking about the fraction of the total supplied by the Moon, which is the comparison that explains why we weigh less on the Moon than on the Earth.

pj
chgo

crosseyedjoe
10-29-2008, 12:01 PM
Actually, it does apply to all real mechanical systems. The assumption of course is that the acceleration doesn't stay positive indefinitely, but eventually reaches zero at some time.

If acceleration never reaches zero, then it's obvious that the velocity is forever increasing and the peak velocity is whatever it is at the present moment.

Your mechanical system is actually the description you gave; "the assumption of course is that the acceleration doesn't stay positive indefinitely, but eventually reaches zero at some time." It's not all "real" mechanical systems. Unless otherwise you assume all "real" mechanical systems behaves that way.

Just one thing "NET acceleration doesn't stay positive."

An object in the system can still have its acceleration even when net acceleration of the whole system is zero. That's why I'm too concern about people using the word "peak" acceleration most specially when applied to just one part of the whole system.

Patrick Johnson
10-29-2008, 12:04 PM
Ah, how is that attractive force normally referred to and what does it imply?

The system YOU and EARTH, has a net zero acceleration. But when you isolate the body YOU and treat it as a separate system, YOU is accelerating by 9.8m/s^2. I was just hoping for people to use terms and the associated system consistently most specially the modifier NET.

Well, maybe so, but it still doesn't seem to have anything to do with the difference in how much we weigh on Earth vs. the Moon. I believe that difference is entirely explained by the difference in their masses/gravitational forces.

And this is even less relevant to pool than it was before.

pj
go

jsp
10-29-2008, 12:16 PM
Well, maybe so, but it still doesn't seem to have anything to do with the difference in how much we weigh on Earth vs. the Moon. I believe that difference is entirely explained by the difference in their masses/gravitational forces.

And this is even less relevant to pool than it was before.
What are you talking about? You mean you don't factor in the moon's gravitational pull when lagging a shot?

softshot
10-29-2008, 12:19 PM
This is true only if you don't care how fast the cue ball moves. The speed of the cue ball will be directly proportional to the speed of the stick at the moment of tip-to-ball contact.

And to the extent that you control the acceleration of the stick you control its velocity to the same extent.

I control acceleration directly.. I control velocity indirectly.. I believe I should be focused on what I can directly control and let the results be what they are.

crosseyedjoe
10-29-2008, 12:56 PM
Well, maybe so, but it still doesn't seem to have anything to do with the difference in how much we weigh on Earth vs. the Moon. I believe that difference is entirely explained by the difference in their masses/gravitational forces.

And this is even less relevant to pool than it was before.

pj
go

The acceleration due to gravity is what changing since your mass remains constant.

dr_dave
10-29-2008, 01:18 PM
You're talking about the total combined gravitational force of the two bodies. I'm talking about the fraction of the total supplied by the Moon, which is the comparison that explains why we weigh less on the Moon than on the Earth.Sorry if I misunderstood your original point.

Regards,
Dave

PS: There is only one force that acts between the earth and moon, and it is equal and opposite on both (i.e., the force the earth exerts on the moon is the same as the force the moon exerts on the earth). This doesn't have a thing to do with pool, but it is an often-misunderstood concept.

sfleinen
10-29-2008, 01:27 PM
I control acceleration directly.. I control velocity indirectly.. I believe I should be focused on what I can directly control and let the results be what they are.
Smorgie's DuneWorm says:

"I controls the spice. I controls the universe. I focuses on what I can directly control (everything) and the results are what they are."

:-D

Patrick Johnson
10-29-2008, 04:08 PM
...There is only one force that acts between the earth and moon, and it is equal and opposite on both (i.e., the force the earth exerts on the moon is the same as the force the moon exerts on the earth). This doesn't have a thing to do with pool, but it is an often-misunderstood concept.

I'd like to understand it better. Can you point me to something?

Thanks,

pj
chgo

dr_dave
10-29-2008, 04:20 PM
I'd like to understand it better. Can you point me to something?Any introductory college physics book covers this. It's called the universal law of gravitation (another one of Newton's contributions to the world). Here's the equation:

F = G * m1 * m2 / d^2

where:
F = equal and opposite force acting between the bodies
G = universal gravitation constant
m1 = mass of body 1
m2 = mass of body 2
d = distance between the CGs of the two bodies

On the surface of the earth:

g = G*M / d^2

where:
g = "acceleration due to gravity"
M = mass of the earth
d = average radius of the earth

To calculate the force acting between the earth and an object (e.g., you) sitting on the surface of the earth:

W = m*g

where:
W = "weight" of the object
m = mass of the object

I hope you find this useful.

Regards,
Dave

PS: ... and this is why the forearm should be perpendicular to the cue at CB impact!!! :)

Patrick Johnson
10-29-2008, 04:49 PM
Dr Dave:
graviational physics lesson...

Thanks, but I'm interested specifically in a conceptual explanation of the notion that the gravitational attraction between two masses is a unitary force that's not the sum of discrete gravitational forces* generated by each.

pj
chgo

*I'm familiar with the General Relativity concept of gravity as spacetime distortion, so I may be taking liberties with the word "force" here.

mikepage
10-29-2008, 04:56 PM
I'd like to understand it better. Can you point me to something?

Thanks,

pj
chgo


I only skimmed this thread, but I think you were comparing the Moon-Patrick force to the Earth-Patrick force, and stating the former is less because the mass of the moon is less.

I think Dave is referring (and thinks you are referring?) only to the Moon-Patrick force. Some people say, incorrectly, that the Moon pulls pretty hard on Patrick because it is pretty massive--while Patrick pulls back only weakly on the Moon. This error (that I don't know whether anybody made here) is one I referred to many moons ago in this letter I had in the Washington Post.



A Weighty Physics Problem
[FINAL Edition]
The Washington Post - Washington, D.C.
Date: Nov 20, 1990
Start Page: a.22
Section: OP/ED
Text Word Count: 294

Three cheers for the new column "Why Things Are" {Style Plus, Nov. 2}. While I enjoyed most of the questions and answers, particularly the two on physics, I am compelled to note that one statement violates Newton's third law of motion.

Why do objects fall at the same rate toward the Earth regardless of their weight? Why does Marlon Brando fall at the same rate as a paper clip when dropped from the Empire State Building? It is because "heaviness is a two-sided coin. As you get heavier, gravity pulls harder, but it is also that much harder to budge you. So weight doesn't make you fall faster or slower." Bravo! Well done. The column should have stopped there.

Instead, it goes on to point out an ever-so-slight complication: because these objects pull on the Earth as they fall, the Earth comes up to meet them, and because Mr. Brando pulls harder on the Earth than a paper clip does, the Earth comes a little faster and a little farther toward him and, lo and behold, Mr. Brando wins, providing the experiments are done one at a time.

All right, but when the column then says that Mr. Brando exerts only an "infinitesimally slight pull" on the Earth, it destroys a fundamental and beautiful symmetry in nature: that forces come in equal and opposite pairs; that every action has an equal and opposite reaction; that no matter how hard you try, you can't lift yourself and the chair you're sitting in by pulling on the sides of the chair. Indeed, by using a bathroom scale and Newton's third law, we can easily measure the strength of Brando's gravitational pull on the Earth. It isn't infinitesimal; it's about 300 pounds!
MICHAEL PAGE Manassas

Cameron Smith
10-29-2008, 05:11 PM
A small technical nit.... It's peak velocity you want, not peak acceleration. Velocity and acceleration are very different in physics, but many people confuse the two. If you hit at peak velocity, you have the most efficient and powerful stroke and likely the most consistent, as well.

Your absolutely right. I got them mixed up. I don't know much about physics, and even less about them in relation to anything other than pool.

JoeyA
10-29-2008, 05:22 PM
with your grip hand forward, you are pushing the cueball not stroking it.
Players, insecure with their stroke, do this trying to guide or control the cueball more. It is called overcompensation.

Bet I could watch you shoot and tell you what shots that are a problem for you.

I like what you write about pool. I think you really know how to play pool. Hope one day to meet you and have my mettle tested.

FWIW, I have seen MANY professional pool players move their hand forward on "cinch shots" and just push the cue ball instead of stroking it. This forward movement of the grip hand cuts down on the speed of the cue ball as JAL points out in one of his posts. This reduced speed is a good thing especially on tight pocket tables and "cinch shots" IMO.

JoeyA

crosseyedjoe
10-29-2008, 05:30 PM
Any introductory college physics book covers this. It's called the universal law of gravitation (another one of Newton's contributions to the world). Here's the equation:

F = G * m1 * m2 / d^2

where:
F = equal and opposite force acting between the bodies
G = universal gravitation constant
m1 = mass of body 1
m2 = mass of body 2
d = distance between the CGs of the two bodies

On the surface of the earth:

g = G*M / d^2

where:
g = "acceleration due to gravity"
M = mass of the earth
d = average radius of the earth

To calculate the force acting between the earth and an object (e.g., you) sitting on the surface of the earth:

W = m*g

where:
W = "weight" of the object
m = mass of the object

I hope you find this useful.

Regards,
Dave

PS: ... and this is why the forearm should be perpendicular to the cue at CB impact!!! :)


Dr. Dave,

I think he is asking if you can express this equation

F = G * m1 * m2 / d^2

to something like this;

F = G * m1 * m2 / d^2 = m1g1(moon's force experience at any point equal to the distance of Earth and moon) + m2g2(Earth's force experience at any point equal to the distance of Earth and moon)

Patrick Johnson
10-29-2008, 07:41 PM
Some people say, incorrectly, that the Moon pulls pretty hard on Patrick because it is pretty massive--while Patrick pulls back only weakly on the Moon. This error (that I don't know whether anybody made here) is one I referred to many moons ago in this letter I had in the Washington Post.

So...

Every time I fall onto the surface of the Earth from 20 feet up (I hate that!) the Earth also falls onto the surface of me. I move 20 feet times the ratio of the Earth's mass to my mass (very close to every bit of 20 feet), the Earth moves 20 feet times the ratio of my mass to its mass (very close to none of 20 feet), we each attain speeds in the same ratio, and the end result is that we slam into each other with the same force (but I'm always the one that goes to the hospital).

Is that what this equal force thing means?

pj
chgo

ShootingArts
10-29-2008, 08:00 PM
Thanks a bunch PJ, one more excuse to add to my arsenal.

"That danged PJ fell again and jiggled the earth just enough my ball jawed the pocket!"

Spoons is sitting somewhere with a bemused and befuddled look on his face, "I just asked a simple question about pool, that is really all I did . . . '

Hu


So...

Every time I fall onto the surface of the Earth from 20 feet up (I hate that!) the Earth also falls onto the surface of me. I move 20 feet times the ratio of the Earth's mass to my mass (very close to every bit of 20 feet), the Earth moves 20 feet times the ratio of my mass to its mass (very close to none of 20 feet), we each attain speeds in the same ratio, and the end result is that we slam into each other with the same force (but I'm always the one that goes to the hospital).

Is that what this equal force thing means?

pj
chgo

arcticmonkey
10-29-2008, 09:18 PM
I spent years trying to get my arm vertical in this plane. It was largely a waste of time. I would have gotten 10 times the benefit from paying attention to where I was placing my bridge hand I believe. Colin

Colin, I read the entire thread and although I got a fuzzy head from the physics discussion :) I was disappointed not to see more discussion about your statement above.

I would be very interested to learn more about how you went about correcting your bridge hand placement. Are there threads out there discussing that very topic?

Thanks

arctic

softshot
10-29-2008, 11:11 PM
Muscle acceleration is tricky because it is under our control if we work at it. My normal tendency is to want to get up to the speed I want to hit the cue ball quickly and basically maintain that speed. However when I work on starting my forward stroke slowly and increasing that speed much more gradually I seem to miss fewer shots. One of the things I need to practice and do practice now and then. I think it should be an ingrained part of my game but it isn't yet.

Hu

I have no proof but my guess would be that if you could somehow pinpoint acceleration and track it through the stroke... and graph it... you would see two distinct outcomes..

one graph is a 45 degree angle ....up until impact.. the right way... the accelerating stroke.. and most decent players once taught could repeat that... semi constantly...


if you graph the player who reaches peak acceleration.. and then attempts to control velocity... you will find a graph that looks more like an EKG graph of a heartbeat.. accelerate stop.. accelerate stop...as the muscle attempts to maintain a velocity.... you are asking a muscle to do something its not designed to do and getting inconsistent results...

when you ask a muscle to do what it does... you get consistent results...

JMO

Patrick Johnson
10-30-2008, 06:00 AM
if you graph the player who reaches peak acceleration.. and then attempts to control velocity... you will find a graph that looks more like an EKG graph of a heartbeat.. accelerate stop.. accelerate stop...as the muscle attempts to maintain a velocity...

I doubt that anybody does this or imagines doing it.

We control acceleration by trying to do it smoothly and evenly throughout the stroke. We control velocity by deciding how fast we want the stick to be moving at the end of that smooth, even acceleration and scaling the whole thing up or down accordingly. It's not either/or. We do both.

The distinction between acceleration and velocity doesn't come into the action; that's just a topic for academic discussion.

pj
chgo

mikepage
10-30-2008, 06:18 AM
So...

Every time I fall onto the surface of the Earth from 20 feet up (I hate that!) the Earth also falls onto the surface of me. I move 20 feet times the ratio of the Earth's mass to my mass (very close to every bit of 20 feet), the Earth moves 20 feet times the ratio of my mass to its mass (very close to none of 20 feet), we each attain speeds in the same ratio, and the end result is that we slam into each other with the same force (but I'm always the one that goes to the hospital).

Is that what this equal force thing means?

pj
chgo

Bingo......

dr_dave
10-30-2008, 08:08 AM
Patrick,

Sorry ... apparently I misunderstood again. I should have known you would know about the universal law of gravitation. You would be surprised how many engineering students (after many years of college-level physics and engineering classes) fail to understand where W=mg comes from.

Without getting into space-time distortion, I think the best explanation is:

For every action, there is an equal and opposite reaction. Regards of the sources of the "forces," if there are two bodies exerting force(s) on each other, the resultant force must be equal and opposite between the bodies.

Sorry if I sounded condescending before. That was not my intention. I know yours physics knowledge and understanding are solid.

Regards,
Dave

Thanks, but I'm interested specifically in a conceptual explanation of the notion that the gravitational attraction between two masses is a unitary force that's not the sum of discrete gravitational forces* generated by each.

pj
chgo

*I'm familiar with the General Relativity concept of gravity as spacetime distortion, so I may be taking liberties with the word "force" here.

Patrick Johnson
10-30-2008, 09:46 AM
Patrick,

Sorry ... apparently I misunderstood again. I should have known you would know about the universal law of gravitation. You would be surprised how many engineering students (after many years of college level physics and engineering classes) fail to understand where W=mg comes from.

Without getting into space-time distortion, I think the best explanation is:

For every action, there is an equal and opposite reaction. Regards of the sources of the "forces," if there are two bodies exerting force(s) on each other, the resultant force must be equal and opposite between the bodies.

OK, I think I'm getting you now. Thanks.

Sorry if I sounded condescending before. That was not my intention.

I'd never suspect you of that. Sorry if I gave that impression.

I know yours physics knowledge and understanding is solid.

Maybe in a colloquial sort of way...

pj
chgo

Bob Jewett
10-30-2008, 09:59 AM
... if you could somehow pinpoint acceleration and track it through the stroke... and graph it... ...
This has already been done twice with ultra-high-speed video. The first time was in the Jacksonville Project in 1998 and the second time was in Dr. Dave's basement this summer.

People have also made accelerometer measurements of pool strokes, and some of them have been posted in previous threads.

A graph of velocity versus position from the Jacksonville Project is available in http://www.sfbilliards.com/articles/1999-06.pdf While that's not acceleration versus time, from the simple relation of velocity and acceleration, it possible to conclude that the acceleration for this particular stroke was zero at impact and the velocity was at its peak.

I'll see if I can post some similar results from the Ft. Collins Project.

Jal
10-30-2008, 10:50 AM
....one graph is a 45 degree angle ....up until impact.. This would be a very inefficient way of generating cue speed and doesn't really resemble players' actual strokes...at least the ones for which we have recorded data (see Dr. Dave's website). Better to have it shaped like a hill. Bob J (and probably other instructors) recommend the stroke be such that impact takes place at around the point where the force is going from positive to negative, ie, having the cue essentially coast into the cueball at constant speed. This corresponds to having the peak at roughly the halfway mark of the graph, timewise. There are several advantages to this and it's certainly a good way to shoot. There are also advantages to having that peak of acceleration occur later into the stroke and then continue to have some positive acceleration right up to impact. But to my knowledge, there's not much to be said for having the peak happen at the very end of the stroke, ie, at impact.

if you graph the player who reaches peak acceleration.. and then attempts to control velocity... you will find a graph that looks more like an EKG graph of a heartbeat.. accelerate stop.. accelerate stop...as the muscle attempts to maintain a velocity.... you are asking a muscle to do something its not designed to do and getting inconsistent results...Yes, that would be pretty bad.

Jim

spoons
10-30-2008, 01:12 PM
Spoons is sitting somewhere with a bemused and befuddled look on his face, "I just asked a simple question about pool, that is really all I did . . . '

Hu

Ha ha... The physics is interesting to me, but it's all far above and beyond the basics that I understand. I suppose that's what you get when you take Physics 101 and your book for the course features a cartoon character named Ringo.

Oddly enough, I got several more direct answers out of this thread than the other thread I created the same day. (although, I am convinced that it's my fault for not being able to articulate my question very well). We did get to the answer eventually, but it took some doing!

ShootingArts
10-30-2008, 02:00 PM
No fault of yours. Just the nature of the forum members, me included, we are easily sidetracked.

Hu




Ha ha... The physics is interesting to me, but it's all far above and beyond the basics that I understand. I suppose that's what you get when you take Physics 101 and your book for the course features a cartoon character named Ringo.

Oddly enough, I got several more direct answers out of this thread than the other thread I created the same day. (although, I am convinced that it's my fault for not being able to articulate my question very well). We did get to the answer eventually, but it took some doing!

smoooothstroke
10-30-2008, 02:35 PM
I have heard that it is best to be straight up and down at contact also.From observing other players I have noticed many top players who's arms are forward at contact.I think as long as your arm angle is not more then 90 degrees you are doing good.

spoons
10-30-2008, 03:06 PM
No fault of yours. Just the nature of the forum members, me included, we are easily sidetracked.

Hu


Eh... no worries. Like I said, the physics is interesting to me, too. And I'm paying a whole lot less for these lessons than I paid to watch Ringo run around acting like a fool!

It's strange to me, though. For as much as I hear about keeping your back arm perpendicular to the cue, the floor, or any other reference point for that matter.... consensus seems to be that it's a great starting point, but that it's really a matter of personal experience and results.

I guess you have to start somewhere when you teach. I just wish more of the instructional folk and authors in this game would acknowledge that individual bodies aren't built the same; and, that finding a way that works for you is really the end goal.

Predictable, repeatable results are paramount. Sure, you've got to be able to stroke the ball a little bit, especially in rotation games. But, it seems like very few matches are ultimately won or lost on stroke shots.

I guess that's why I started this thread- to see if anyone knew of a major difference between perpendicular and past perpendicular that would be holding me back in the years to come. Anyway, thanks for all the input everyone. Please resume your physics discussion ;)

<------ stepping off soap box.

JoeyA
10-30-2008, 04:33 PM
This would be a very inefficient way of generating cue speed and doesn't really resemble players' actual strokes...at least the ones for which we have recorded data (see Dr. Dave's website). Better to have it shaped like a hill. Bob J (and probably other instructors) recommend the stroke be such that impact takes place at around the point where the force is going from positive to negative, ie, having the cue essentially coast into the cueball at constant speed. This corresponds to having the peak at roughly the halfway mark of the graph, timewise. There are several advantages to this and it's certainly a good way to shoot. There are also advantages to having that peak of acceleration occur later into the stroke and then continue to have some positive acceleration right up to impact. But to my knowledge, there's not much to be said for having the peak happen at the very end of the stroke, ie, at impact.


Jim

Jim, would you mind listing the advantages of having the cue coasting into the cueball at constant speed?

What are the advantages of having the peak acceleration occur later into the stroke and continuijng to having some positive acceleration right up to impact?

Thanks,
JoeyA

Patrick Johnson
10-30-2008, 04:46 PM
Jim, would you mind listing the advantages of having the cue coasting into the cueball at constant speed?

The one I always hear (and that makes obvious sense to me) is that it gives the greatest chance of hitting the CB at the speed you want because you don't have to time the hit so precisely (more margin for timing error). Maybe Jim knows more.

What are the advantages of having the peak acceleration occur later into the stroke and continuijng to having some positive acceleration right up to impact?

A disadvantage would be the converse of my point above: when the stick is constantly changing speed you have to hit the CB at a very precise moment to get the speed you want.

Sorry to butt in. As you were.

pj
chgo

softshot
10-31-2008, 02:05 AM
This has already been done twice with ultra-high-speed video. The first time was in the Jacksonville Project in 1998 and the second time was in Dr. Dave's basement this summer.

People have also made accelerometer measurements of pool strokes, and some of them have been posted in previous threads.

A graph of velocity versus position from the Jacksonville Project is available in http://www.sfbilliards.com/articles/1999-06.pdf While that's not acceleration versus time, from the simple relation of velocity and acceleration, it possible to conclude that the acceleration for this particular stroke was zero at impact and the velocity was at its peak.

I'll see if I can post some similar results from the Ft. Collins Project.


that is some excellent information... but even your own graph shows acceleration after impact... the speed increases after contact..


what are we measuring? speed of the cue? friction between the grip hand and the wrap?... weight of the cue vs the ball? or acceleration of the bicep?? was the experiment done with a perfect pendulum stroke...??

Randy turned me on to the Jacksonville experiments.... I am not arguing that you guys got good data... I am not questioning it...

you are measuring ... from what I see... acceleration and velocity as it relates to a cue stick... valid data...

I am coming from a biometrics position.. what the shooter is doing while those effects are occurring..?

they are accelerating their bicep twards its own center.. that is the only thing a muscle is capable of doing....

and at the end of the day that is the ONLY thing they can control... so they should focus on that...

control what is under your control.. and let the results be what they are....

I still believe that if you accelerate through the cueball.. you will attain the most consistent results... ...

JMO

Jal
10-31-2008, 02:13 AM
Jim, would you mind listing the advantages of having the cue coasting into the cueball at constant speed?

What are the advantages of having the peak acceleration occur later into the stroke and continuijng to having some positive acceleration right up to impact?

Thanks,
JoeyAJoey, I should note that the following is based on computer modeling of the physics of pushing an object forward and not with any insight into the mechanics of the human arm. I did try to generate a force curve that looked similar to one supplied by John Pizutto here at Dr. Dave's website:

http://billiards.colostate.edu/technical_proofs/new/TP_A-9.pdf

What the program did was to compare different length pendulum style strokes for a fixed bridge distance. By stroke length, I mean the distance traveled by the tip from the beginning to the end of the stroke sans any intervening collision with a cueball. The cue's speed was calculated as it reached the cueball for different stroke lengths and various injected errors. The errors produced deviations in stroke length via timing, grip position and length of backstroke (starting position of the tip). The effects of deviations in bridge length, and peak force were also calculated.

Coasting at impact (having the acceleration pass from positive to negative) was taken as a baseline stroke length and set the "standard" grip position. It was assumed that for every inch forward of this grip position, stroke length would be decreased by two inches, and for every inch rearward, stroke length would be increased by two inches. The rationale and assumption behind this was that the angle of the forearm where the transition from positive to negative acceleration occurs is fixed (barring a timing error). This seemed consistent with trials done with my cue.

According to this then, the advantages of coasting are:

- It uses the least amount of energy to get the cue up to some speed.

- Cue speed is less sensitive to the various imposed errors compared to having the cue decelerate before impact. Particularly noteworthy is its reduced sensitivity to small deviations in bridge length of around 5-10%.

The advantages of stretching the stroke out and continuing to accelerate at impact are:

- It can generate more cue speed given the same peak force and/or it requires less peak force to reach some particular speed.

- Cue speed is less sensitive to all of the deviations than either coasting or decelerating at impact, except for small variations in bridge length and peak force. With all three modes, cue speed is equally affected by deviations in peak force.

A major assumption was that the basic shape of the force-time curve is the same regardless of stroke length (grip position), only being stretched or contracted along the time scale. Lacking more information, this was necessary and the idea was just to compare different stroke lengths anyway, keeping other variables the same. Given that we're dealing with the human arm and human volition, many things can change. But if you step back from the numbers and mull over the general physics, I think the conclusions have a pretty fair chance of being applicable despite those changes. I have found that moving my grip hand back of vertical by about 3 inches did produce more draw distance by roughly what was predicted (very informal test). I would guess that you could effect something similar, or more so, with elbow drop instead.

Not recommending anything, just trying to compare them from a purely physics point of view. I do think it argues strongly against peaking early and then decelerating, from having your grip hand well-forward.

Jim

JoeyA
10-31-2008, 08:37 AM
Thanks Jim.

JoeyA

Bob Jewett
10-31-2008, 10:42 AM
... what are we measuring? speed of the cue? ...
The quantity that is plotted on the vertical axis is the speed of the cue stick versus time. The sudden drop just after the first peak is caused by the tip hitting the ball -- about 50% of the stick speed is removed in a thousandth of a second. The return of the stick speed to about 80% of its maximum value occurs after the ball has left the tip. This smaller second peak is from the hand, which does not slow down during the nearly instantaneous collision, pushing the stick partly back up to speed.

In order to determine the acceleration of the stick, you need to plot the slope of the graph for each time. Since the slope of the curve is more or less zero when the tip hits the ball, the acceleration for the stroke shown is more or less zero when the tip hits the ball.

Jaden
10-31-2008, 10:50 AM
As many people have pointed out, it's a good starting point and there is valid reasons for having your elbow at a 90 degree angle at contact. It does come down to personal preference, but at the same time, it is important to understand why it can be helpful to developing consistency.

I just found this thread and it is LONG so forgive me if this has already been stated.

By having the forearm pointing straight down at the point of impact, you have gravity pulling straight down on the arm, this limits the amount of tangential force and makes it easier to have a closer to perfectly straight point of contact. This is not to say that it is not possible to do without being perfectly perpendicular, but it is easier for the vast majority of people this way. There are too many top players with unorthodox strokes for this to be a perfect representation of what is necessary, but it does make it easier for the average player and will have the highest percentage for the highest percentage of players.

Jaden.

softshot
11-01-2008, 01:13 AM
This smaller second peak is from the hand, which does not slow down during the nearly instantaneous collision, pushing the stick partly back up to speed.



Exactly!!

.. the hand is still accelerating .. because the shooter is accelerating through the ball..

I don't care what the physics are... ( I can't change the laws of nature)

I care about how I can control the physics... and I have the best control of impact velocity.. when I accelerate through the cueball.. I am allowing my muscle..to do what it does naturally..

all the physics a pool SHOOTER needs to know is to accelerate evenly through the cueball...and to be able to do that at different rates... you accelerate through a lag the same way you accelerate through a break shot...

Deadon
11-01-2008, 02:12 AM
Thanks for the thoughtful replies everyone, there are some great tidbits in here.

I've long been a proponent of the importance of predictable results over raw ability, but obviously if I could combine the two, I'd like to do that.

I'm not sure what I'll do in the end, but I appreciate the perspectives of folks on here.

I think if there's one thing that would push me over the edge, it would be somehow knowing that I could achieve the same results with less effort. From what I'm reading here, it sounds like making contact peak acceleration is generally regarded as more important than the actual position along the pendulum swing. Right?


Spoons;

Peak acceleration is at the point where your arm is perpendicular to table. That is why it is recommended, has little to do with having the cue level also. As you go forward past that point, the tip of the cue goes down, not up as others have suggested, and the forward movement slows. Think of a piston in a car engine, at what point is the piston moving up the fastest?

That is the best result with the least effort. Doesn't mean that its best for you, as you may feel more comfortable doing otherwise. Its just the best technical place to start.

Jal
11-01-2008, 09:04 AM
...I don't care what the physics are... ( I can't change the laws of nature)Of course you don't need to know physics in a formal way, but you do need to understand it at gut level. Since you can't change it, it's generally a good idea to not try to violate its laws.

I care about how I can control the physics... and I have the best control of impact velocity.. when I accelerate through the cueball.. I am allowing my muscle..to do what it does naturally..What you say about accelerating through could very well be right - physics supports this.

all the physics a pool SHOOTER needs to know is to accelerate evenly through the cueball...If by "evenly", you mean to accelerate the stick forward during the stroke at a more or less constant rate, this just doesn't happen. It's not "natural" for the muscles to do this.

Jim

Patrick Johnson
11-01-2008, 09:50 AM
Peak acceleration is at the point where your arm is perpendicular to table. That is why it is recommended, has little to do with having the cue level also.

It's recommended for both reasons, and in fact level cue* may be more important than peak acceleration.

pj
chgo

*What's really meant by this is "the part of the stroke's arc where the grip hand is traveling parallel with the stick". The stick is never really level.

softshot
11-01-2008, 11:53 AM
If by "evenly", you mean to accelerate the stick forward during the stroke at a more or less constant rate, this just doesn't happen. It's not "natural" for the muscles to do this.

Jim

I worded that poorly by evenly I mean a gradual constant increase that peaks at impact

Jal
11-01-2008, 12:07 PM
Peak acceleration is at the point where your arm is perpendicular to table.From what you said after after this, you obviously mean peak velocity, not peak acceleration. It's a nitpick, but there is an important difference.

...As you go forward past that point, the tip of the cue goes down, not up as others have suggested, and the forward movement slows.While the part in bold (my edit) is probably substantially correct, it's not clear how much volitional control you have over this. You may be able to change the timing significantly even with a pendulum stroke. Do you have any info that supports this, either way?

That is the best result with the least effort.It does require the least effort and is a very good way to shoot. It's debatable as to whether it's necessarily the best way. Final cue speed is less sensitive to some stroking errors when "accelerating through", in theory.

Jim

Jal
11-01-2008, 01:32 PM
I worded that poorly by evenly I mean a gradual constant increase that peaks at impactI think I get the gist of what you're saying, which is to have a smooth stroke without any jerkiness. Probably no one would disagree. Technically though, if you were to graph the cue's rate of change of speed against time, ie, its acceleration against time, it would be anything but constant. This has been done with accelerometers and examples were linked to earlier. It goes from zero to some peak value, then back down to zero, or thereabouts.

But more in line with what you're saying are plots of speed against distance, as shown in this video by Dr. Dave, Bob J. and Dave Gross.

http://billiards.colostate.edu/high_speed_videos/new/HSV_B-40_stroke_analysis.wmv

If you draw a line tangent to one of the curves at any point, that is the rate of change of speed against distance at that point of the curve. While not constant (the one for Dave Gross comes pretty close), the tangents show a fairly smooth and gradual decrease over distance.

Jim

ShootingArts
11-01-2008, 02:16 PM
I just watched the video a few times. As I suspected, acceleration seems to peak early in the stroke for most people and falls off as we approach the cue ball. Velocity increases but at a much slower rate than it did at peak acceleration. This has little to do with the mechanical properties of the forearm angle to the cue stick and everything to do with the nature of our muscles.

Dave Grossman is the exception to the rule. Although his acceleration doesn't increase it is very near constant throughout the stroke with a slight blip at the end, due to wrist or shoulder movement I suspect. This is a distinctly different way of shooting and I believe perhaps a better way. Sometimes I focus on a slow start of my forward stroke and what I describe as a gathering of power. I deliberately gradually increase speed all the way to the cue ball. This isn't my natural stroke as my natural stroke more resembles Bob's and Dr. Dave's, a fairly early ascent to peak acceleration with it falling off as I approach the cue. I have worked to make my start a bit more gradual than if I was swinging a hammer for example but I am usually far from Dave Grossman's approach.

I do think that constant or increasing acceleration might be the better stroke for maximum control of accuracy hitting the cue ball. It is also obvious that speed control would be easier with the strokes of Bob Jewett and Dr. Dave. As always, we live with trade-offs, there isn't a perfect solution to most issues we deal with in the real world and stroke just seems to be one more place that we compromise regardless of which stroke we choose.

Hu






I think I get the gist of what you're saying, which is to have a smooth stroke without any jerkiness. Probably no one would disagree. Technically though, if you were to graph the cue's rate of change of speed against time, ie, its acceleration against time, it would be anything but constant. This has been done with accelerometers and examples were linked to earlier. It goes from zero to some peak value, then back down to zero, or thereabouts.

But more in line with what you're saying are plots of speed against distance, as shown in this video by Dr. Dave, Bob J. and Dave Gross.

http://billiards.colostate.edu/high_speed_videos/new/HSV_B-40_stroke_analysis.wmv

If you draw a line tangent to one of the curves at any point, that is the rate of change of speed against distance at that point of the curve. While not constant (the one for Dave Gross comes pretty close), the tangents show a fairly smooth and gradual decrease over distance.

Jim

Jal
11-01-2008, 04:36 PM
I just watched the video a few times. As I suspected, acceleration seems to peak early in the stroke for most people and falls off as we approach the cue ball. Velocity increases but at a much slower rate than it did at peak acceleration....Agreed.

Dave Grossman is the exception to the rule. Although his acceleration doesn't increase it is very near constant throughout the stroke with a slight blip at the end, due to wrist or shoulder movement I suspect.His acceleration is not constant, or even close to being constant. Acceleration is the change in speed divided by the time it took for that change to occur. Tangent lines to the curves on those graphs represent the change of speed divided by the distance it took for the change to occur. Since these are curves and not straight lines, the tangent lines represent the 'instantaneous' change of speed divided by distance traveled while that change took place, when that distance is very small (infinitesimal). This happens to be equal to the acceleration, as just defined, divided by the cue's speed at that moment, or equivalently, the force acting on it divided by its momentum.

Sorry to harp, but it's difficult to communicate when people have different definitions. The one just offered is the standard one.

Jim

ShootingArts
11-01-2008, 05:05 PM
I gotta look again. He is talking about one thing and graphing something else.

Hu


Agreed.

His acceleration is not constant, or even close to being constant. Acceleration is the change in speed divided by the time it took for that change to occur. Tangent lines to the curves on those graphs represent the change of speed divided by the distance it took for the change to occur. Since these are curves and not straight lines, the tangent lines represent the 'instantaneous' change of speed divided by distance traveled while that change took place, when that distance is very small (infinitesimal). This happens to be equal to the acceleration, as just defined, divided by the cue's speed at that moment, or equivalently, the force acting on it divided by its momentum.

Sorry to harp, but it's difficult to communicate when people have different definitions. The one just offered is the standard one.

Jim

ShootingArts
11-01-2008, 05:42 PM
Jim,

I went and reviewed the video several more times and I still see a much more consistent acceleration throughout the part of the stroke graphed considering Dave G's stroke. Breaking down the percentage of maximum speed over time or distance gives a similar result. Dr. Dave and Bob Jewett achieve most of their contact speed early in their stroke and have largely stabilized velocity, acceleration is nearing zero, when they hit the cue ball. Dave Grossman's velocity increase is spread far more evenly over the length of the stroke that is graphed. In simple layman's terms, the acceleration appears near constant over the length of the stroke.

Looking at the way the human body works, it appears that Dave Grossman's muscles are still fully engaged at cue ball impact while there is little if any muscular effort in Dr. Dave and Bob Jewett's strokes at that point, at least in the strokes graphed.

At the end of the day I am interested in the stroke that most consistently pockets balls and gives me shape on the next one. If speed control were the primary criteria, and it often is, I would prefer Bob J's and Dr. Dave's stroke. However if the greatest possible accuracy hitting the cue ball and object ball were most important I would favor Dave G's stroke.

My reasoning is simple. Our muscles in our arms are not well balanced, some are stronger than others. Also they are not perfectly synchronized. That is why we have to put so much effort into gaining and maintaining a straight stroke. These muscles in a steady state, contracting comparatively gently under light load will deliver the cue more accurately than if they are in transition, starting to relax.

Our bodies aren't designed to work like machinery and trying to compare their actions too closely to the workings of machinery leads to bad science. Physics isn't a strong point of mine. However I studied how our muscles work and how to make them work better for about a decade.

Hu

Deadon
11-01-2008, 06:29 PM
From what you said after after this, you obviously mean peak velocity, not peak acceleration. It's a nitpick, but there is an important difference.

You are correct, didn't want to get too techie, cue forward speed would be the appropriate term as I wanted to avoid the vector discussion in using the term velocity. As you did when you explained acceleration without including the vector component ie speed or direction can be acceleration.

[/QUOTE]While the part in bold (my edit) is probably substantially correct, it's not clear how much volitional control you have over this. You may be able to change the timing significantly even with a pendulum stroke. Do you have any info that supports this, either way?[/QUOTE]

Because of the arc of the arm as it travels past the lowest point, as it goes up, the forward vector of the cue would have to slow to some degree.

[/QUOTE]It does require the least effort and is a very good way to shoot. It's debatable as to whether it's necessarily the best way. Final cue speed is less sensitive to some stroking errors when "accelerating through", in theory.[/QUOTE]

This was an answer to spoons question on the best way with the least effort. Best way overall is what works best for the player.

dr_dave
11-03-2008, 10:48 AM
... I am interested in the stroke that most consistently pockets balls and gives me shape on the next one. If speed control were the primary criteria, and it often is, I would prefer Bob J's and Dr. Dave's stroke. However if the greatest possible accuracy hitting the cue ball and object ball were most important I would favor Dave G's stroke.

My reasoning is simple. Our muscles in our arms are not well balanced, some are stronger than others. Also they are not perfectly synchronized. That is why we have to put so much effort into gaining and maintaining a straight stroke. These muscles in a steady state, contracting comparatively gently under light load will deliver the cue more accurately than if they are in transition, starting to relax.Dave Gross, by "accelerating into the ball," is contracting his muscles more than he needs to achieve the desired cue speed. Bob's and my strokes in HSV B.40 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-40.htm) are using less muscle effort to create the same cue speed. Dave Gross builds up the speed more slowly at first, so he needs to work harder to build up the rest of the speed later in the stroke. I would think this would lead to less accuracy, in general (although, Dave Gross is a great player).

Regards,
Dave

PS: The muscle transitions during the stroke are more complicated than many people think. For more info, see the 2nd Q&A here:
http://billiards.colostate.edu/threads/stroke.html#SPFF

Jal
11-03-2008, 01:41 PM
Dave Gross, by "accelerating into the ball," is contracting his muscles more than he needs to achieve the desired cue speed. Bob's and my strokes in HSV B.40 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-40.htm) are using less muscle effort to create the same cue speed. Dr. Dave,

I'm not sure what you mean by "less muscle effort." According to the force-time curves I've looked at, it takes less peak force to get the cue up to some particular speed when "accelerating through." This should be true of sinusoidal-like curves in general, but I haven't really looked for exceptions.

Dave Gross builds up the speed more slowly at first, so he needs to work harder to build up the rest of the speed later in the stroke.In terms of energy expenditure throughout the entire stroke, this is likely true.

It's hard to say anything with absolute confidence since I don't think anyone here has studied how the force-time curve varies with different stroke lengths. It sounds like Hu (ShootingArts) does know a lot about the muscles themselves.

Jim

dr_dave
11-03-2008, 03:58 PM
Dr. Dave,

I'm not sure what you mean by "less muscle effort." According to the force-time curves I've looked at, it takes less peak force to get the cue up to some particular speed when "accelerating through." This should be true of sinusoidal-like curves in general, but I haven't really looked for exceptions.Jim,

Thank you for pointing out my error. I was a little careless with my "intuition." I prepared a TP with analysis and plots ... probably similar to what you have done already. Here it is:

TP B.4 - Stroke speed and acceleration vs. distance

I'd be curious whether or not you (and/or others) agree with my conclusions at the end. Also, let me know if you spot any errors.

In terms of energy expenditure throughout the entire stroke, this is likely true.I agree. The energy delivered to the cue is obviously the same for any stroke if the cue speed (just before CB impact) is the same. Work done = energy = 1/2mv^2. However, the energy expended by the complex muscle physiology might vary significantly from one stroke type to another.

Regards,
Dave

softshot
11-04-2008, 02:14 AM
ENT]

I'd be curious whether or not you (and/or others) agree with my conclusions at the end. Also, let me know if you spot any errors.

Regards,
Dave

compare a muscle and a rocket....both are pure acceleration

which one maintains a more consistent trajectory over distance... overcoming other implied forces...

does an accelerating rocket resist gravity better than a non accelerating rocket... yes because it influences the forces involved to a greater extent.. than it would if it didn't apply it's controllable force.

on a pool table gravity is not the concern ... friction is...

an accelerating stroke overcomes friction.. in the same way a rocket overcomes gravity..

and in both instances you gain a greater control of trajectory.. and you do it by utilizing the only force under your control.. in the most effective way...

if a rocket is on the trajectory you want it on.. you should fire the main engine and accelerate straight through the other forces...

rather than

trying to coast through using your booster rockets to maintain trajectory...

acceleration is your freind.... and the bonus is you have complete direct control over it...

Patrick Johnson
11-04-2008, 07:24 AM
[snip comparison of rockets and arms]

The cue ball doesn't know or care whether your stick is accelerating, coasting or decelerating - it only knows how fast your stick is going at the moment of impact. Your stick's speed at impact is all that determines how far the cue ball goes and how spin (especially follow and draw) works on it.

Since your stick's velocity at impact is the only thing that matters to the cue ball, it's the only thing that should matter to you. You should adopt the method of accelerating your stick that ensures the stick will be moving at the speed you want when it hits the cue ball.

If you "accelerate through" the cue ball, you ensure that your stick's speed is changing (accelerating) at the time it hits the cue ball and is traveling at the speed you want for only an instant - and that instant is likely to occur before or after you hit the cue ball.

But when your stick reaches its peak speed it moves at nearly the same speed (while it transitions from accelerating to decelerating) for a few moments rather than one instant, giving you a larger "window of opportunity" to hit the cue ball at that speed. In other words, peak speed ("coasting") is an easier speed target to hit because it's not so much of a moving target.

The obvious conclusion is that, while it's important to control your stick's acceleration, you should control it so it ends (reaches peak speed) as your stick reaches the cue ball, not so it continues through the cue ball.

Conveniently, peak speed (the end of "speeding up" acceleration) occurs naturally at about the "bottom" of your stroke - where your tip is also traveling in the straightest line for the longest time. So it makes sense (and is probably easiest) to try to make all three things - reach peak speed, reach bottom center of your stroke, and hit the cue ball - happen simultaneously.

pj
chgo

randyg
11-04-2008, 09:30 AM
Nice post Patrick!....SPF=randyg

whitewolf
11-04-2008, 10:03 AM
Here's my dilemma:

I've been told by players much more accomplished than I that I should work on getting my back arm perpendicular at contact. Nearly every book, article, AZB post, etc. that discusses fundamentals seems to agree.

When I play, my arm is usually forward of perpendicular at contact. I wouldn't say dramatically, but very clearly visible to anyone who's looking. I've done this for years, because it's more comfortable, it feels more natural to me, and I seem to get significantly more consistent results.

I've tried several times to "fix" my stroke, by moving my grip hand back, or addressing the ball differently- for months at a time, even - with no appreciable result other than feeling awkward at the table, and playing significantly worse than I know I'm capable. I feel like I have enough "stroke" playing my usual way, to do anything I need to do at the table, but I can't help but wonder if there's a compelling reason to try fixing my mechanics again.

Ultimately, I don't want my game to be limited by something like this, so I thought I'd put the question to the board. What are the benefits, scientific or otherwise, of addressing the cue ball with your back arm perpendicular to the ground?

Thanks!

Well I had a chance to go to the US Open this year and I pointed out to my friend that most of the pros were NOT perpendicular. Their arms were slighty forward from the vertical plane.

And, for the pros who really get down over the shot, it is impossible for the forearm to be perpendicular if the elbow is up in the sky because the anlge at the elbow is NOT 90%. Nonetheless, those pros who were down low had their foreamrs tilted slightly forward.

I have proclaimed in the past that this is similar to the 'forward press' in golf, whereby just before making the swing the hands move slightly forward on the plane of the backswing. What this does is to cue your mind on the PLANE.

It is my theory that this is what pool players do naturally. If you don't believe me, try tilting the forearm slightly back and see how awkward this is.

Regards, WW

Jal
11-04-2008, 10:50 AM
...If you "accelerate through" the cue ball, you ensure that your stick's speed is changing (accelerating) at the time it hits the cue ball and is traveling at the speed you want for only an instant - and that instant is likely to occur before or after you hit the cue ball.

But when your stick reaches its peak speed it moves at nearly the same speed (while it transitions from accelerating to decelerating) for a few moments rather than one instant, giving you a larger "window of opportunity" to hit the cue ball at that speed. In other words, peak speed ("coasting") is an easier speed target to hit because it's not so much of a moving target.

The obvious conclusion is that, while it's important to control your stick's acceleration, you should control it so it ends (reaches peak speed) as your stick reaches the cue ball, not so it continues through the cue ball.Patrick,

The cue's speed at impact is the result of what has taken place during the entire stroke. The argument you just presented focuses in on the last few moments and is valid as far as it goes. But when you look at the stroke from start to finish, it's at least plausible that accelerating through can result in better speed control. The physics of why this could be true is fairly straightforward. Naturally, it gets muddled up when the human element is added. However, these unknowns apply just as much to the "coasting through" argument as to the "accelerating through" argument. You don't gain much accuracy if you're coasting at the wrong speed.

All in all, it may be that coasting is the best way since it happens to coincide, more or less, with zero movement of the tip in the vertical plane. It's also likely a little more energy efficient. But the "best speed control" part of the argument is not so clear cut, imo.

Jim

softshot
11-04-2008, 01:37 PM
snip Patrick making the same argument he made several pages ago

and now we have come full circle..

human muscles can maintain acceleration much more consistently than they can maintain velocity..

I want consistent control. so I will let my muscles do what they naturally are good at...

Patrick Johnson
11-04-2008, 04:36 PM
JAL:
...it's at least plausible that accelerating through can result in better speed control.

"Better speed control" means creating a better chance for the correct stick velocity and impact with the cue ball to occur simultaneously. How could "accelerating through" (accelerating continuously up to and past impact) do this?

pj
chgo

Patrick Johnson
11-04-2008, 04:44 PM
human muscles can maintain acceleration much more consistently than they can maintain velocity...

Human muscles don't "maintain" peak velocity - it's "maintained" naturally by the fact that your muscles have stopped accelerating your arm.

I will let my muscles do what they naturally are good at...

They're naturally good at doing nothing during "peak velocity" - it's what they naturally do.

pj
chgo

Bob Jewett
11-04-2008, 05:40 PM
... human muscles can maintain acceleration much more consistently than they can maintain velocity. ...
That's not implausible, but what sort of study determined this? Do you have a reference?

As for what we can sense of the motion, I think we can sense at least three factors in motion and controlling motion: position, velocity and acceleration. It's not clear to me that separating them out somehow gives either a better feeling of what's going on or more control. Also, I suspect that we sense force far more than acceleration, but if you use the same cue stick all the time they are directly proportional.

I think we may also be able to sense -- have a feel for -- jerk, which is the rate of change of acceleration. Minimizing jerk also seems to be important in developing a consistent stroke.

Jal
11-04-2008, 06:33 PM
"Better speed control" means creating a better chance for the correct stick velocity and impact with the cue ball to occur simultaneously. How could "accelerating through" (accelerating continuously up to and past impact) do this?Good question.

During the forward stroke the cue is being accelerated up to some speed (duh). Take the time from the start of the stroke up to impact and divide it into small intervals (ideally infinitesimal). During each of these intervals the magnitude of the acceleration will have a particular value. Multiply the magnitude of the acceleration by the length of the time interval. The cue's final speed at the commencement of impact will be the sum of all these products, one for each interval. So its final speed depends on its acceleration at each interval throughout the entire stroke, not just at the end. In that sense, none (or any group) of the time intervals is more important than any other.

When accelerating through to obtain some particular speed, the curve of acceleration plotted against time is generally flatter than when not accelerating or decelerating at impact. This makes it less sensitive to timing errors, i.e., shifting it, or some portion of it, right or left on the time scale. It's kind of hard to explain why this is true without a diagram, which I can't offer at this time.

It has to be said, however, that small variations in bridge length favor coasting through if no adjustments are made for them. It then becomes a question of how well these variations are noticed by the player and what adjustments are made. This element adds considerable fuzziness to the whole issue.

Jim

softshot
11-04-2008, 10:48 PM
Human muscles don't "maintain" peak velocity - it's "maintained" naturally by the fact that your muscles have stopped accelerating your arm.



They're naturally good at doing nothing during "peak velocity" - it's what they naturally do.

pj
chgo

you don't maintain peak anything... thats why it's the peak...

a muscle doing nothing... isn't moving

a muscle in mid contraction is accelerating.. at some rate.

muscles accelerate towards their own center it is all they CAN do.. or other muscles are pulling and stretching them back..

that's why a pause is a good thing it makes every other muscle stop

then allows you to concentrate on the accelerating contraction of the bicep muscle.. because at the end of the day that is all a stroke is... if you are doing it right..

Patrick Johnson
11-04-2008, 10:48 PM
Me:
"Better speed control" means creating a better chance for the correct stick velocity and impact with the cue ball to occur simultaneously. How could "accelerating through" (accelerating continuously up to and past impact) do this?
When accelerating through to obtain some particular speed, the curve of acceleration plotted against time is generally flatter than when not accelerating or decelerating at impact. This makes it less sensitive to timing errors, i.e., shifting it, or some portion of it, right or left on the time scale.

But the objective is to have a flatter curve of velocity around the moment of impact. How is "accelerating through" conducive to this?

pj
chgo

softshot
11-04-2008, 10:57 PM
That's not implausible, but what sort of study determined this? Do you have a reference?

As for what we can sense of the motion, I think we can sense at least three factors in motion and controlling motion: position, velocity and acceleration. It's not clear to me that separating them out somehow gives either a better feeling of what's going on or more control. Also, I suspect that we sense force far more than acceleration, but if you use the same cue stick all the time they are directly proportional.

I think we may also be able to sense -- have a feel for -- jerk, which is the rate of change of acceleration. Minimizing jerk also seems to be important in developing a consistent stroke.

currently I cannot site the specific source of that information but it does exist...

I was at the library a month or so ago with some time to kill and on a whim started looking at books on sports medicine and things like physics and the human body.. and I learned quite a bit..... I can't get you the specific passage.. off hand right now.. but the next time I am at the library I will attempt to find it..

the passage on acceleration as a natural muscle function .. was in relation to a baseball pitcher throwing an off speed pitch .. and how they have to remember to accelerate the arm consistently even though it was at a slower speed.. and how it is easier than you think .. because consistent acceleration is a natural ability of muscles.

Jal
11-05-2008, 01:40 AM
But the objective is to have a flatter curve of velocity around the moment of impact. How is "accelerating through" conducive to this?It might help to imagine two extreme cases.

Suppose the acceleration was absolutely constant throughout. A graph of it against time (or distance) would then be a horizontal line - as flat as flat can be. The final speed would be the area under the curve, that is, the product of that constant magnitude of acceleration times the length of time it took for the cue to reach the cueball. If you were to attempt to stretch or contract this acceleration line over time, it would be exactly the same and you would end up with the same final speed, assuming a fixed bridge length. In other words, under the assumption that the acceleration is constant, stretching or contracting it really has no meaning.

The opposite extreme would be an acceleration curve that shot up to some peak value in a very short time, then back down to zero just as fast. The cue would acquire its velocity in almost an instant, then coast at this speed the rest of the way, assuming no decelerating force was subsequently applied. As with the flat line just described, this speed would be the area under that spike-like curve. But now if you were to stretch it out over time, i.e., change the timing, it would have a very different area underneath it. Generally speaking, the steeper the rise and fall, the more sensitive the area is to timing.

I think (hope) that illustrates the general principle. With more realistic curves which do rise and fall but at a slower rate, the same applies; it's just not as obvious and the benefit of making them flatter, to whatever extent that can be done, isn't as dramatic.

Jim

mikepage
11-05-2008, 07:56 AM
Good question.

During the forward stroke the cue is being accelerated up to some speed (duh). Take the time from the start of the stroke up to impact and divide it into small intervals (ideally infinitesimal). During each of these intervals the magnitude of the acceleration will have a particular value. Multiply the magnitude of the acceleration by the length of the time interval. The cue's final speed at the commencement of impact will be the sum of all these products, one for each interval. So its final speed depends on its acceleration at each interval throughout the entire stroke, not just at the end. In that sense, none (or any group) of the time intervals is more important than any other.

When accelerating through to obtain some particular speed, the curve of acceleration plotted against time is generally flatter than when not accelerating or decelerating at impact. This makes it less sensitive to timing errors, i.e., shifting it, or some portion of it, right or left on the time scale. It's kind of hard to explain why this is true without a diagram, which I can't offer at this time.

It has to be said, however, that small variations in bridge length favor coasting through if no adjustments are made for them. It then becomes a question of how well these variations are noticed by the player and what adjustments are made. This element adds considerable fuzziness to the whole issue.

Jim

Jim - I'm not SURE I understand your argument, but I think I do. Tell me if the jist is right here.

My understanding of Jim's argument
**************
Assume we can generate a desired peak force (acceleration) accurately, and assume we ramp up to this peak acceleration and then back down like a hump of a sine wave. The area under this acceleration versus time "hump" up to any point in time is the speed the stick has achieved up to that time. If we strike the ball when the stick is coasting, like Patrick is endorsing in this thread, that means we have generated the speed corresponding to the area under the entire hump.

Now instead of our sine hump lasting for 1.0 seconds, suppose the whole thing is wider in time and lasts for 1.1 seconds (but has the same height). This new stick will be moving faster at the end of the hump (more area under this wider hump)

Or if the whole hump lasted 0.9 seconds instead of 1.0 seconds--that stick would be moving more slowly at the end.

But if you look at a 0.9-second hump right on top of a 1.0 second hump (starting at the same instant of time), then things are more interesting. We know the area under the 0.9 is less, but for the early parts of the stroke--for the first few tenths of a second, the area is actually more because the 0.9 hump is rising faster. Then on the back half the area under the 0.9 becomes less by a greater degree. That's how it is overall less.

Jim's argument is if you only go about halfway down the far side the areas (and thus speed of the stroke) are the same.

Thus at a particular point on the downhill, the stick speed is insensitive to this "timing variable."

I will say what I think of this argument later, but I'd first like to know whether I basically have it right.

Jal
11-05-2008, 05:15 PM
Jim - I'm not SURE I understand your argument, but I think I do. Tell me if the jist is right here.

My understanding of Jim's argument
**************
Assume we can generate a desired peak force (acceleration) accurately, and assume we ramp up to this peak acceleration and then back down like a hump of a sine wave. The area under this acceleration versus time "hump" up to any point in time is the speed the stick has achieved up to that time. If we strike the ball when the stick is coasting, like Patrick is endorsing in this thread, that means we have generated the speed corresponding to the area under the entire hump.

Now instead of our sine hump lasting for 1.0 seconds, suppose the whole thing is wider in time and lasts for 1.1 seconds (but has the same height). This new stick will be moving faster at the end of the hump (more area under this wider hump)

Or if the whole hump lasted 0.9 seconds instead of 1.0 seconds--that stick would be moving more slowly at the end.

But if you look at a 0.9-second hump right on top of a 1.0 second hump (starting at the same instant of time), then things are more interesting. We know the area under the 0.9 is less, but for the early parts of the stroke--for the first few tenths of a second, the area is actually more because the 0.9 hump is rising faster. Then on the back half the area under the 0.9 becomes less by a greater degree. That's how it is overall less.

Jim's argument is if you only go about halfway down the far side the areas (and thus speed of the stroke) are the same.

Thus at a particular point on the downhill, the stick speed is insensitive to this "timing variable."

I will say what I think of this argument later, but I'd first like to know whether I basically have it right.Dr. Page,

I'm still confident in my argument, but ain't arrogant or dumb enough (close) to not realize that when a professor gets on your case, you've got trouble.

My argument does not really resemble your take on it. It's based entirely on the relative flatness of the curves. Actually, when the computer spit out the numbers (this was years ago), it surprised me. I then made up a diagram to see why this is true, and just concocted the response to Patrick's question in lieu of the diagram (that computer isn't working).

I've been looking over the math to see if I had an expression for the derivative of the final velocity with respect to phase frequency (w in sin(wt), where the force function is Asin(wt), or with harmonics, A1sin(wt)+A2(sin(2wt)...), but don't. It's complicated by the fact that I use an iterative process to find the phase angle (wt) at impact. I don't know if a closed analytic expression exists, but I'll see if I can derive one which will make things more obvious, one way or the other. (Obviously, you could do it too, and with greater ease, but may have better things occupying your time).

I agree with your general statements about the .9, 1.0, and 1.1 second curves, but didn't really follow the conclusion about the speed sensitivity to timing as drawn from them, which methinks you're prepared to demolish anyway. Yeah, I seem to be evasive, but really didn't look at it in the way you presented it...at least I don't think so.

(Got my hardhat on, hammer as needed.)

Jim

Jal
11-06-2008, 03:20 AM
deleted by Jal

Jal
11-06-2008, 03:09 PM
...I've been looking over the math to see if I had an expression for the derivative of the final velocity with respect to phase frequency...As a double check of arguments given earlier, I calculated the sensitivity of the velocity at impact to changes in overall timing for the simple force function F=Asin(wt). This is the derivative dVi/dw, where "Vi" is the cue's speed at impact. If "ti" is the time it takes for the cue to reach the cueball, and m its mass, the derivative is:

dVi/dw = [A/(mw^2)][2(wti - sin(wti))/(1 - cos(wti)) - (1 - cos(wt))]

When coasting at impact, wti is equal to pi. When "accelerating through", wti is something less than pi. To make a comparison, the peak force amplitude "A" has to be adjusted to equalize the velocity and bridge distance traveled. For some different w, w', the adjusted amplitude A' is given by:

A'/A = (w'^2/w^2)[(w'ti' - sin(w'ti'))/(wti - sin(wti))

Using 0.9pi and 0.8pi for w'ti' as examples, the sensitivity (derivative) is reduced to 0.69 and 0.46 of its value when wti=pi (coasting), respectively. These are significant reductions, imo.

Jim

Jal
11-07-2008, 01:06 PM
...
dVi/dw = [A/(mw^2)][2(wti - sin(wti))/(1 - cos(wti)) - (1 - cos(wt))]

Using 0.9pi and 0.8pi for w'ti' as examples, the sensitivity (derivative) is reduced to 0.69 and 0.46 of its value when wti=pi (coasting), respectively.In case someone is actually interested enough to verify the math, I should note that a factor of sin(wti) was accidentally dropped from one of the terms for the derivative. It should read:

dVi/dw = [A/(mw^2)][2(wti - sin(wti))sin(wti)/(1 - cos(wti)) - (1 - cos(wt))]

Then instead of the cited reductions of 0.69 and 0.46, they are 0.72 and 0.46, respectively. (The second one doesn't change within the 2-digit precision.)

Jim

mikepage
11-07-2008, 02:13 PM
What I was describing and could describe better with a diagram was a graphical way to compute this derivative, dVi/dw --or, to be clear, the partial derivative of Vi with respect to w at fixed A.

Imagine a hump corresponding to frequency w. Then imagine another hump starting at the same time of frequency w + dw that is superimposed over the first one. Though the two humps almost fall on top of one another, the second hump is a little shorter and overall has a little less area under it (higher w means quicker stroke). This difference in area is dVi. Divide that by dw and you have the derivative dVi/dw evaluated at the end of the hump, i.e., at wt=pi. This derivative is negative.

Now think a little about what that area difference looks like. The shorter hump (the w + dw) actually rises faster in the first half. So if you were to evaluate dVi/dw at, say, wt=pi/2, the derivative would be positive instead of negative (positive area change divided by dw). Then when you start falling down the back side, the shorter hump drops more quickly and has less area under it.

So the left-side area difference is positive (say, +3) and the right side area difference is negative (say, -5) such that the total area difference is -2 (negative as it should be.)

If we want to find the point on the downhill for which dVi/dw is zero, then we just need to go down the hill until the right-side area difference is -3, i.e., just enough to cancel the left-side area difference.

At this point, dVi/dw is zero and the speed is insensitive to the "timing" of the stroke for fixed A.


In case someone is actually interested enough to verify the math, I should note that a factor of sin(wti) was accidentally dropped from one of the terms for the derivative. It should read:

dVi/dw = [A/(mw^2)][2(wti - sin(wti))sin(wti)/(1 - cos(wti)) - (1 - cos(wt))]

Then instead of the cited reductions of 0.69 and 0.46, they are 0.72 and 0.46, respectively. (The second one doesn't change within the 2-digit precision.)

Jim

mikepage
11-07-2008, 02:18 PM
Dr. Page,

I'm still confident in my argument, but ain't arrogant or dumb enough (close) to not realize that when a professor gets on your case, you've got trouble.[...]

Hey I'm just a B-player and I haven't been shooting much in the last month and my eyes aren't what they used to be and I just changed tips and I'm coming in cold off the street and ....

Patrick Johnson
11-07-2008, 03:02 PM
What I was describing and could describe better with a diagram was a graphical way to compute this derivative, dVi/dw --or, to be clear, the partial derivative of Vi with respect to w at fixed A.

Imagine a hump corresponding to frequency w. Then imagine another hump starting at the same time of frequency w + dw that is superimposed over the first one. Though the two humps almost fall on top of one another, the second hump is a little shorter and overall has a little less area under it (higher w means quicker stroke). This difference in area is dVi. Divide that by dw and you have the derivative dVi/dw evaluated at the end of the hump, i.e., at wt=pi. This derivative is negative.

Now think a little about what that area difference looks like. The shorter hump (the w + dw) actually rises faster in the first half. So if you were to evaluate dVi/dw at, say, wt=pi/2, the derivative would be positive instead of negative (positive area change divided by dw). Then when you start falling down the back side, the shorter hump drops more quickly and has less area under it.

So the left-side area difference is positive (say, +3) and the right side area difference is negative (say, -5) such that the total area difference is -2 (negative as it should be.)

If we want to find the point on the downhill for which dVi/dw is zero, then we just need to go down the hill until the right-side area difference is -3, i.e., just enough to cancel the left-side area difference.

At this point, dVi/dw is zero and the speed is insensitive to the "timing" of the stroke for fixed A.

Will this be made available with English subtitles?

Alternatively, can you say whether you've concluded anything about acceleration's vs. velocity's importance to hitting the cue ball at the right speed?

pj
chgo

mikepage
11-07-2008, 04:58 PM
Will this be made available with English subtitles?

Ok... when I have time ;-)

Alternatively, can you say whether you've concluded anything about acceleration's vs. velocity's importance to hitting the cue ball at the right speed?

pj
chgo

Both arguments are mathematically correct, and both are of the form

[All else being equal,]
Ball speed is least sensitive to
[type of error in stroke]
when
[particular condition]
is satisfied.

I think your argument is the more reasonable one because I think your [all else being equal] is better satisfied and your [type of error in stroke] is imo more closely related to the kinds of errors that plague our strokes. But these judgments are qualitative. So I'll explain my reasoning when I can.

Jal
11-08-2008, 12:16 PM
What I was describing and could describe better with a diagram was a graphical way to compute this derivative, dVi/dw --or, to be clear, the partial derivative of Vi with respect to w at fixed A.

Imagine a hump corresponding to frequency w. Then imagine another hump starting at the same time of frequency w + dw that is superimposed over the first one. Though the two humps almost fall on top of one another, the second hump is a little shorter and overall has a little less area under it (higher w means quicker stroke). This difference in area is dVi. Divide that by dw and you have the derivative dVi/dw evaluated at the end of the hump, i.e., at wt=pi. This derivative is negative.

Now think a little about what that area difference looks like. The shorter hump (the w + dw) actually rises faster in the first half. So if you were to evaluate dVi/dw at, say, wt=pi/2, the derivative would be positive instead of negative (positive area change divided by dw). Then when you start falling down the back side, the shorter hump drops more quickly and has less area under it.

So the left-side area difference is positive (say, +3) and the right side area difference is negative (say, -5) such that the total area difference is -2 (negative as it should be.)

If we want to find the point on the downhill for which dVi/dw is zero, then we just need to go down the hill until the right-side area difference is -3, i.e., just enough to cancel the left-side area difference.

At this point, dVi/dw is zero and the speed is insensitive to the "timing" of the stroke for fixed A.Thanks for the clarification. I have reservations about drawing any conclusions from it since w+dw also causes a change in ti, ti--->ti+dti. It's difficult (for me) to see how this will affect the area without some hindsight from the math. The graphical arguments I've used were to illustrate what the math was already indicating. If there are doubts as to whether dVi/dw decreases as wti becomes less than pi, I would prefer that either you did the math, or looked over my derivation to check for errors. However, from your response to Patrick, it looks like you don't disagree.

Jim

mikepage
11-09-2008, 06:48 AM
Thanks for the clarification. I have reservations about drawing any conclusions from it since w+dw also causes a change in ti, ti--->ti+dti. It's difficult (for me) to see how this will affect the area without some hindsight from the math. The graphical arguments I've used were to illustrate what the math was already indicating. If there are doubts as to whether dVi/dw decreases as wti becomes less than pi, I would prefer that either you did the math, or looked over my derivation to check for errors. However, from your response to Patrick, it looks like you don't disagree.

Jim

Hi Jim. I don't disagree. I get a little different expression for the derivative though

dV/dw = A/mw^2 [ wt*sin(wt) + cos(wt) -1]

This is zero when the stuff in square brackets is zero which occurs when wt = 0.742*pi, in other words about halfway down the hill. Maybe I made an error here. I don't know. But I think my graphical argument is rigorous and proves that your conclusion about dV/dw being zero somewhere on the downhill is right.

mikepage
11-09-2008, 08:31 AM
[...]
Alternatively, can you say whether you've concluded anything about acceleration's vs. velocity's importance to hitting the cue ball at the right speed?

pj
chgo

Think about a person walking.

On every step, the person places his foot RIGHT below his center of mass. Now ask the person to walk faster. The center of mass (person) moves faster, the legs swing faster and/or longer, and still those feet get planted right below the person's center of mass on each step. Ask the person to start trotting. Same thing. This is something we're really good at.

What would happen if the person started trotting and the leg didn't swing around quite fast enough, or didn't swing out quite far enough? The person would plant a foot BEHIND his center of mass and fall forward.

My point is we are remarkably good at COUPLING the speed we are moving to the way in which we swing our legs to achieve the desired result --planting a foot below our center of mass.

It's not to the same degree, but I think we are remarkably good at coupling the length of our stroke to the peak force to achieve a desired stick speed. That is, if a one-pocket player is hitting an object ball three rails to the vicinity of his pocket, he can do it with a short stroke or a medium stroke or a long stroke. If he shortens the length of his backstroke by half an inch, he is good at generating the right amount of extra force on the forward stroke to get the desired outcome.

So if the force versus time curve for his stroke looks like the hump of a sine curve

F(t) = A sin(wt)

then I'm saying players are remarkably good at coupling together w and A to achieve the desired speed of the stroke. w can vary over a pretty wide range and the player will naturally also change A over a wide range to compensate.

This makes consideration of how the quality of the outcome varies with respect to w holding A fixed (like Jal does) or considering how the quality of the outcome varies with respect to A holding w fixed [which nobody's talked about yet and favors decelerating at impact ;-)] just not very well related to the nature of our actual errors.

Think about the hot and cold water controls in a shower--two degrees of freedom, two variables. But like A and w, H and C are two degrees of freedom that are strongly coupled together. What we care about is the temperature of the water. If we increase the intensity of H and of C together, we can keep the temperature of the water the same. This suggests a coordinate transformation to more natural variables (ones that aren't so coupled)

The new coordinates are I (intensity) and T (temperature), and they're obtained from the old ones by

I = H + C

T = H - C

and these are the better controls in a shower (pull it out further to get more water and twist it to change the temperature)

shovelmd
11-09-2008, 08:42 AM
wow, that's crazy if i had to think about all of that i would never be able to drop a ball. don't forget to add top or bottom english to your formula.:smile:

Jal
11-09-2008, 12:49 PM
wow, that's crazy if i had to think about all of that i would never be able to drop a ball. don't forget to add top or bottom english to your formula.:smile:It's essential for the next level of position play. Efren was kind enough to send the formula along, however, I find that I'm still limited to +/- half a table length of precision....maybe he's playing games with us.

Jim