Question about follow thru

[DoomCue]

I think your analysis is right on, but I have a couple observations and questions.

It appears that you think the best success in force application will occur when the cue does what is "natural". I think this is a completely valid and intelligent method that is likely to lead to good results.

However, doesn't your analysis of stroke acceleration POST-contact of the cue ball depend entirely on whether someone has taken this "natural" approach. That is to say, it appears that your theoretical stroke is constantly losing velocity while mine is constantly gaining velocity. Your theoretical stroke is constantly losing velocity because it takes a "natural" path to the cue ball. As I understand it, in your scenerio, gravity helps to increase the velocity of the cue towards the cue ball pre contact, having its peak velocity at contanct, and as the cue levels out it begins to lose velocity. Why can't the player operate on the cue such that it continues accelerating through the ball rather then having the cue perform this "natural" function of losing velocity at its level point?

You asked, "If the cue did positively accelerate throughout the entire time period we call a stroke, then why does the cue come to a stop at the end of the stroke?"

The cue comes to a stop because your body cannot continue indefinitely. There is a limit to how far your elbow will go past vertical or how far your shoulder will drop.

I am fairly certain you will still disagree with me, but I am interested to hear why. You may end up changing my understanding. BTW, I don't think I studied momentum in physics (at least not as deeply as force), is there an equation to describe it, and if there is and you know it, would you mind telling me? I am in law school now, and it has been a long time since high school physics.

kollegedave

What's at work here is conservation of momentum. Momentum is mathematically expressed as p=mv. Momentum = mass X velocity. Rather than go into a physics dissertation, I've found a web-site which does an excellent job of explaining simple conservation of momentum physics. Once you've read that, do a Google search on "impulse momentum change theorem" which should enlighten you further. I know people get tired and bored of seeing physics on this forum, so if you have any more physics-related questions, feel free to PM me.

-djb

 

[kollegedave]

You have a PM.

kollegedave

What's at work here is conservation of momentum. Momentum is mathematically expressed as p=mv. Momentum = mass X velocity. Rather than go into a physics dissertation, I've found a web-site which does an excellent job of explaining simple conservation of momentum physics. Once you've read that, do a Google search on "impulse momentum change theorem" which should enlighten you further. I know people get tired and bored of seeing physics on this forum, so if you have any more physics-related questions, feel free to PM me.

-djb

 

[FLICKit]

Clarification Needed

Always be aware, that when you get into a very technical discussion, you have to be very very specific about the details of what you're talking about.

Without the proper details, you can both be arguing, what sounds like the same issue, but not really. Thus, you can be arguing and both be right for the most part ignoring a few tiny inaccuracies (such is human). Not gonna be a discussion that comes to a fruitful conclusion if you're both right, and don't recognize that the other one is as well.

I've noticed a number of things where both of you may have very different details. Here are some details that you may both need to clarify in order to be truely having the same discussion.

This will be basic information that most everyone knows. But you may not have very specifically clarified before entering into the detailed discussion.

1. Type of stroke
For the most part, you both may think you're talking about the same thing
a. Perfect pendulum swing - exactly what it says pendulum (i.e. clock, or more accurately weight on an end of a string). This swing would be to pull your arm back, eliminate all muscles and execute a perfect swing.
b. Since the arms do have muscles that are used (often unknowlingly) other swings most often occur. Acceleration - The muscles in your arm increase the speed of the cue past the point of contact. Yet, this increase is not infinite of course, because factors cause your arm to stop (either muscles at the end, body interference, or outside interference - i.e. table or arm stop...).
c. Deceleration - or as you guys have stated negative acceleration. We all know what it is, no need to clarify.

2. Contact Point - Where are your cue stick and cue ball contacting
a. Precisely at the bottom of the pendulum
b. Before reaching the bottom of the pendulum
c. After reaching the bottom of the pendulum

3. Specific momentum (p=mv). You guys are both probably assuming that there is enough mass and velocity involved to overcome the weigt/inertia of the cue ball.

4. A factor that you may be flat out ignoring is collision - the almost instantaneous change in reaction from two bodies in contact.

When the person mentioned that he can get the ball to stop, or small draw, with a short distance shot by hitting CB above center. When you add in collisional factor, then this can be true. Note: very important to recognize that he said small distance.

5. Another factor involved would be the cue tip. The cue tip compresses and depresses, which creates acceleration effects as well.

Other factors may come into play as well like velocity and how low you hit cb and type of draw you're trying to execute (nip, snap, ...)


Most people would assume that they are discussing a perfect pendulum swing, with contact point at bottom of the pendulum, but in actuality they usually aren't.

This type of swing, although sounds good, would not be the best way to execute draw. Although, for those who are having trouble with draw, it's a good place to start, to ensure that they are executing a proper stroke, before actually doing what is necessary to properly draw a ball.


Other issues involved would be are you trying to execute maximum draw, or controlled draw? Maximum draw would head towards only 1 solution, which is whatever is the best at the time (surprisingly different styles of draw, could possibly produce maximum draw at various stages in progression).


Ultimately, the discussion about draw or follow through, might be better served as a discussion about producing spin (note not maximum spin) in a controlled manner.

Have to eliminate many of the variables, before trying to have such a detailed discussion.

 

[Rackin_Zack]

Always be aware, that when you get into a very technical discussion, you have to be very very specific about the details of what you're talking about.

Not to mention that everyone is treating force, velocity, acceleration, and momentum as scalars, at least in what posts I've read, when they are actually vectors. It's still elementary physics, but it does change the calculations a bit.

 

[DoomCue]

Not to mention that everyone is treating force, velocity, acceleration, and momentum as scalars, at least in what posts I've read, when they are actually vectors. It's still elementary physics, but it does change the calculations a bit.

I haven't done any rotational transforms, either. Does that mean the discussion is invalid? Do you really want to see all the sines, cosines, and thetas?

All the nitpicking and minutiae aren't part of the point here. The issue kollegedave and I are discussing is whether or not extended follow through results in increased contact time. That's all. Nothing about verticality at impact, nothing about cue tips, nothing about pendulum swings, nothing about vector quantities, etc. We've taken the discussion to PM, so if anybody else wants to join in, send me a PM.

-djb

 

[FLICKit]

I haven't done any rotational transforms, either. Does that mean the discussion is invalid? Do you really want to see all the sines, cosines, and thetas?

All the nitpicking and minutiae aren't part of the point here. The issue kollegedave and I are discussing is whether or not extended follow through results in increased contact time. That's all. Nothing about verticality at impact, nothing about cue tips, nothing about pendulum swings, nothing about vector quantities, etc. We've taken the discussion to PM, so if anybody else wants to join in, send me a PM.

-djb

What you're missing out on, is that you all have to have the same baseline for the discussion. If not, then you're talkin apples and oranges.

You may assume that you're all talking about the same thing, but may be surprised to discover the areas where you're not.

Kollegedave has postulated that contact time is increased with increased follow through, and hence more spin is applied because force is time-dependent. My question was meant to provoke a little more thought - if acceleration is zero (velocity is constant), then force is zero. Somehow, though, the CB still moves. How can that be?

Where you're a little misleading on this is that the Net force is 0... But there is still Velocity and Mass. There just isn't any change in velocity. So its movement is constant. A change in velocity, would have a Net Force.

I do disagree with you. Long follow through or short, I don't believe there's any effect whatsoever on spin. The only benefit of a follow through is an increase in consistency of stroke. Let the cue come to a natural stop. There's no reason to waste energy trying to stop it, and there's no reason to try to control it. Let it be natural.

Long and short followthroughs have significant impacts on draw shots. Once again, for the discussion you have to clarify some points.

Obviously we have to clarify that no matter which stroke we're making same contact at the same distance below center of cue ball.

For short or long follow through
are we starting with a long backswing
are we starting with a short backswing
are you assuming you can ignore backswing and allow whatever backstroke the player wants

True, a long follow through will increase consistency in the stroke, but that consistency will manifest itself in many ways.

The ability to deliver a stroke at a consistent speed.
The ability to deliver a stroke with a more gradual acceleration (if desired)
Increases ability to deliver a straighter stroke - a short follow will result in cue stopping shortly after contact, whereby the muscles will magnify a jolt to the left or right due to the stopping motion.

A shorter stroke can help to deliver a stroke with a more rapid change in acceleration through the point of contact with the cue ball. That can result in more spin.

A longer stroke will help to deliver the cue a longer distance with less effort and overcome the frictional elements resulting from the table felt.

A shorter stroke will have more difficulty in accomplishing the same thing.


Also be aware from your point of allow it to stop without wasting energy.
Although true most of the time, there are situations where you're not allowed the long follow through stroke (i.e. two balls too close to each other). Once again, have to take into account the variables.

During the stroke, as the forearm approaches vertical, it is accelerating. Once it reaches vertical, acceleration is zero. Once the forearm has passed vertical, it is negatively accelerating.

Once again, you have to clearly define your baseline.
If you're assuming perfect pendulum swing, which as was stated, rarely occurs, then you're right.
Most players, especially the pros, use at least a little acceleration in their swing, especially for a draw shot. Thus when the arm is vertical, there can still be acceleration in the swing. Acceleration usually continues until some distance past the point of contact with the cue ball. Then a more rapid deceleration occurs in the remainder of the swing - and still allows for enough room for natural deceleration to occur.

So what's really at work here? What causes the cue ball to move or spin if acceleration is zero and therefore force is zero?

Now, your confusing things by talking apples and oranges. This is where it's especially critical to be precise.

If the cue stick has zero acceleration like you say, then it is being delivered with a constant velocity. When referring to the spin of the cue ball, the cue stick is not your frame of reference, but instead the cue ball is your frame of reference.

Thus, the cue ball experiences a force below its core center. This contact point is below the core center of the cue ball. The cue stick causes the bottom portion of the cue ball to move and accelerate, while inertia causes the top part of the cue ball to resist movement. Thus, cue ball spin develops.

Torque = moment of inertia * angular acceleration
Rotation


Nobody is talking about nitpicking. But, in order to engage in such a technical discussion, you do have to have all the proper baselines defined.

 

[kollegedave]

After Doom Cue's first PM to me, I understood his point and am now in agreement with him on the science. With Doom Cue's permission I will post his first PM to me, because his response did help me understand the science better.

kollegedave

 

[Cue Crazy]

Cue Crazy: Can you really stop your cueball using top english?????randyg

Well Randy, I am no Pro, and for the most just play for fun, so take what I say with a grain of salt As I'm sure you already know, not so well with alot of distance between the cueball & object ball, but closer shots I can somewhat stop, when alot of people would need to hit a rail after contact. I'm not going to sit here blowing smoke , saying I can stop on a dime everytime with top, and to be honest I am more unconcious about mixing My stroke to do It, so I'm sure it could be argued. It seems to me that It is more of a touch shot type thing, so probably more in the stroke & speed then the english. Top english does'nt naturally stop the Cue ball with follow-thru that I am aware of, unless maybe when there is a slight bit of spin out, and contact with the object ball causes It to stop, that is something that would only happen for me if I was really in stroke, and had the feel for the felt on the table. Now I can easily do stop shots just under Middle english, or a hair lower as others do, but sometimes I need to stop in My target area with top instead, depending on the layout, shot, or obsticles preventing me from hitting below center ball. I would rather just follow the layout of the balls around the table using stop shots until I have to do something more extreme to keep the run alive.

Unfortunatly I learned the hard way & came up as a loose type shooter in the begining that learned to play more mechanical over time, and was not taught a purely mechanical game from the start. I tend to use spin more then I should, cheat pockets, and that sort of thing. For instance I can cheat the angles using english, and make the shots, even though I am aiming slightly off center pocket. This is especially helpfull on straight in, scratch type shots, with no angle to hit the back rail with, and set the cue ball up for shape on the next shot. I can basically create My own angles, and not have to take just what's there naturally. I also use this on backward cut shots that do not even seem possible to make to most people that see it done. Also use it to make tuff shots on scratch angles to keep from scratching the cue ball. The amount of spin is an important factor also on the scratch angles.

I also do someting like that with bottom english, where I cheat the pocket, control the spinout, pull the cue ball almost sideways a few inches, or more, for a slightly better angle on the next shot then I would have had with just the stop shot. I am sure there are others here that play that way also, because where I live, we have people from all over come here, or move here, and there are several other decent shooters that shoot the same style, and mix both styles together.

Keep in mind that I try to stick with the diamond system of position play most of the time, as others do, I just mix this other stuff up when I feel good with it, and I like My odds better.

It's not always as safe or consistent, but I always have respect for guy that can make things happen to keep the run alive, or shoot out at anytime If I try to safe him too often.

Anyway, I have no secret on the top english stop, that anyone is not already aware of. If I did I would pass It on. It's something that I just do kind of unconsiously to stay in position, so have not analized the physics of what's actually happening in My stroke. Greg C

 

[DoomCue]

Where you're a little misleading on this is that the Net force is 0... But there is still Velocity and Mass. There just isn't any change in velocity. So its movement is constant. A change in velocity, would have a Net Force.

Where am I misleading anything? If velocity is constant, force is zero. Period. Sure, there's velocity and mass, nobody's disputing that. You're missing the point entirely.

Long and short followthroughs have significant impacts on draw shots.

Prove it.

Once again, for the discussion you have to clarify some points.

Obviously we have to clarify that no matter which stroke we're making same contact at the same distance below center of cue ball.

For short or long follow through
are we starting with a long backswing
are we starting with a short backswing
are you assuming you can ignore backswing and allow whatever backstroke the player wants

Funny, kollegedave understands what we were discussing. Who cares about backswing when the discussion between kollegedave and me is whether or not an increase in follow through leads to increased contact time?

True, a long follow through will increase consistency in the stroke, but that consistency will manifest itself in many ways.

The ability to deliver a stroke at a consistent speed.
The ability to deliver a stroke with a more gradual acceleration (if desired)
Increases ability to deliver a straighter stroke - a short follow will result in cue stopping shortly after contact, whereby the muscles will magnify a jolt to the left or right due to the stopping motion.

A shorter stroke can help to deliver a stroke with a more rapid change in acceleration through the point of contact with the cue ball. That can result in more spin.

A longer stroke will help to deliver the cue a longer distance with less effort and overcome the frictional elements resulting from the table felt.

A shorter stroke will have more difficulty in accomplishing the same thing.

Can you actually prove any of these statements?

Also be aware from your point of allow it to stop without wasting energy.
Although true most of the time, there are situations where you're not allowed the long follow through stroke (i.e. two balls too close to each other). Once again, have to take into account the variables.

Or make some up....

Once again, you have to clearly define your baseline.
If you're assuming perfect pendulum swing, which as was stated, rarely occurs, then you're right.
Most players, especially the pros, use at least a little acceleration in their swing, especially for a draw shot. Thus when the arm is vertical, there can still be acceleration in the swing. Acceleration usually continues until some distance past the point of contact with the cue ball. Then a more rapid deceleration occurs in the remainder of the swing - and still allows for enough room for natural deceleration to occur.

ALL players (not most players) have to accelerate the cue, otherwise it would never move. Acceleration usually continues until some distance past the point of contact? Are you sure about that?

Now, your confusing things by talking apples and oranges. This is where it's especially critical to be precise.

If the cue stick has zero acceleration like you say, then it is being delivered with a constant velocity. When referring to the spin of the cue ball, the cue stick is not your frame of reference, but instead the cue ball is your frame of reference.

Thus, the cue ball experiences a force below its core center. This contact point is below the core center of the cue ball. The cue stick causes the bottom portion of the cue ball to move and accelerate, while inertia causes the top part of the cue ball to resist movement. Thus, cue ball spin develops.

Torque = moment of inertia * angular acceleration
Rotation


Nobody is talking about nitpicking. But, in order to engage in such a technical discussion, you do have to have all the proper baselines defined.

OK, here we go, here are your proper baselines defined. There's a cue ball, here's a stick. If I hit the cue ball with the stick, will the stick stay stuck to the cue ball longer if I have an exaggerated follow through? That's it, nothing more, nothing less.

-djb <-- thought I made that point in my last post...

 

[Cue Crazy]

I can unequivocally guarantee that you are not getting draw hitting above center, no matter how much you "snap" the cue/stroke. What you are doing when "snap" the cue is you think you're hitting above center but you're really dipping the tip to center or below. If you were hitting above center and stopping the ball you'd be defying the laws of physics, in which case you'd win a Nobel Prize if you could explain it...lol.

LOL, I wish I could do, and explain that one. No let me better explain, that is just what some local ol timer called it back many years, and not the correct term as far as I know. I guess maybe extreme topspin would have been a better term. maybe you can tell me the correct term for it if that is incorrect, because I have never really been up on all the pool terms, just love to play. I am not actually drawing the cue ball back. what I am talking about is what you are probably already aware of, and able to do as well. It is forward momentem, but I am using spin to excelerate the cueball after contact.I guess the draw in his term was only an example of the spinout that takes place before the cueball speeds up in a forward direction. My bad, Guess I could have used a better term to explain it Greg



On the ball stopping issue, I tend to aggree that on closer shots the short tap stroke, slight spin & speed control is part of what seems to stop it for Me. If I follow, then the cue rolls past My mark.
Just think about a duck sitting in the side pocket just hanging, and your straight on the shot. This Is just Me, But If I were for instance to shoot it straight on with no english, and followed I would probably scratch. but if I ever so slightly stall stroke & control My speed at the same time, the cue b will stop where It made contact. I do shoot these somewhat unconsiously, so it's very possible Maybe I am missing something, and what I think is actually taking place is not what's really happening. would love to know If there is a better way, or anything besides that, that will improve that area of my game. It's seems to work for Me though. If the ball is away from the pocket, then It seems as if the speed of the cue ball is transfered to the object ball and the cue stops when I stroke the shot that way.

 

[Cue Crazy]

Yeah, Think My slow brain is catching on now . Please excuse My simple mind here, but Is what you are actually discussing, almost a push type situation? The amount of time the cue tip is making contact with the cueball, correct? does the tip stay on longer? If that's what your talking about then I think I understand. On this paticular shot that is actually a good question. My simplemind still tells me yes and no.
I guess My stroke Is not as consistent as others therefore I have to go with the shorter/ longer stroke issue mentioned. I also aggree that the shorter will have the greater deal of dificulty. probably why I like to use it so much, for the challenge of controlling It.


You fellers seem fairly smart While on that subject, maybe someone can tell me, Can you be called on a push ,even if there is ample space between the cue ball and object ball? The other night I had a nice ,smooth stroke going, and some guy kept saying "nice push stroke", even though there was around 3 feet between the cb & objectball, and It was also shot down the rail when he would say It. Is It possible to push from that far away? I was'nt sure how to take it, If he was sugesting I did a push shot, or It was actually a compliment. there was no double contact, and the stroke was just as smooth as could be, wish it was always that good. The funny thing is- the table It was on was slow as a turkey on thanksgiving, and I actually had to use alot of topspin which should have had more of a pop to the stroke, as well as a shorter stroke. Think the guy was just jerking My chain? the games were'nt going his way, so I just assumed It may have been a suttle way of trying to shark Me, because It was'nt like he was trying to call me on anything. Anytime I push or foul I usually am fully aware I did, and am the first one to admitt it, even when My oponet did not know I did It. I have'nt ever had to be called for a push that I remember. My stroke is actually not good enough to push that well most of the time LOL. Greg

 

[JohnnyP]

natural follow through

I asked Wayne Norcross (ex straight pool champ from the early '70's) about my grip last night, and he proceeded to tell me about my follow through.

He'd been watching me practice, and told me I was forcing wrist action into my stroke. He says, if it happens, it happens, but don't force it. Let your wrist hang loose.

He went on to say that he releases the cue on the forward stroke, "just like Mosconi", he said. He explained that this way, you don't deaden the stroke, and you get a natural follow through. The momentum of the cue carries it straight forward, through the cueball, so you don't have to worry about dropping your elbow or twisting your wrist at the impact. You've let the cue go, now let it do the work. He also said it doesn't matter how far the cue slips, or if it slips at all, as long as it is released.

I took his advice, and my short game showed an immediate improvement, with very controlled amounts of draw and stun.

He had encouraged me last year to get a heavier cue than my 17 oz toothpick I've been playing with for forty years, so I ordered a 19 oz 62" Viking (hits like a dream). After I removed the 1 oz bolt, it weighes in at 19.3 oz.

He said "There's a reason why all the top players use a heavier cue than you have." At the time, he didn't elaborate, but last night he explained that a heavier cue helps with the natural follow through (release the cue).

John's cues

By the way, why is the shaft wood on my old cue yellow? I like it, and don't really care for white wood. It was made by a no-name cue maker in '66. The cue repair guy at Triangle Billiards told me to hang on to it.

 

[Bob Jewett]

... A longer follow through would imply that the cue stayed in contact with the cue ball longer, thus imparting a greater force upon the ball...F=MA. There is a time component to acceleration as it measures the rate velocity increases. Thus, if the cue is in contact with the cue ball for a longer period of time, then it is easier to impart a high degree of spin.

kollegedave

Actually, it turns out that for higher-velocity shots, the tip is in contact for a shorter time. I think you will be more successful in getting more spin on the ball if you hit it farther from center and don't worry about where in the stroke you are accelerating.

As for the original poster-- forget about that part of the stroke unless it keeps your mind off other things you shouldn't be thinking about when you pull the trigger.

 

[Bob Jewett]

Could you get maximum spin from no follow through? I would suggest that neither you nor anyone else could.
..

If you mean a maximum quality of spin, that is a lot of spin for the speed, then the answer is that you can play a very high quality shot with the tip not going beyond the center of the cue ball. If you mean maximum RPMs on the cue ball, like Massey and Sayginer get, then a normal stroke will go several inches beyond the cue ball's original location.

 

[Bob Jewett]

The force applied to the cue ball is equal to the mass of the stick multiplied by its acceleration (hence the saying accelerate through the ball). F=MA. In the case of a pool cue the mass is relatively constant (18-20 oz.) The force applied to the ball is therefore essentially directly proportional to the acceleration through the ball. Accordingly, it becomes necessary to understand what acceleration is and how to generate it. Acclerlation is a measure of the rate velocity increases. If the cue strikes the cue ball (at 0 m/s) but its velocity continues to increase (acceleration), then if would seem that the strike in question would continue, as the cue would sort of catch up to the ball it just struck. Perhaps, a microscopic double hit.

Force exerted on the cue ball is essentially dependent on a time measurement in acceleration. If time is to matter in this scenerio, why would it matter but to describe or provide information on the time in which the cue is in contact with the cue ball?

If one attempts to strike the cue ball and stop his cue right after his stopping point, then the follow through is small and I would suggest so is the action on the cue ball. Conversely, it would seem that if the follow through were longer, then the action on the cue ball would be greater. Why? if not that the follow through provides some benefit. If the follow through does provide a benefit, then why if not that it applies a force for a longer period of time?

kollegedave

As far as I can tell, the above is a complete misunderstanding of the physics involved.

 

[kollegedave]

After having the help of DoomCue, I think I said that I agreed with his viewpoint earlier in the thread.

kollegedave

As far as I can tell, the above is a complete misunderstanding of the physics involved.

 

[HittMan]

what's ......... got to do with it.

I'm confused! What does the length of the follow through have to do with the cue ball?.....SPF-randyg

IMHO length of follow thru is a visualization tool...and probably a fairly good one because it is pretty well known...kind'a like old sayings...they don't get old without a grain of truth. There will always be exceptions, of course, but it does make me curious...What do you use for a visualization tool (assuming we agree it is one). I'd like to know what you do so I can try it for a while and see if it works for me. I'm so old and dumb I need crutches.

 

[HittMan]

reference

I do this sometimes too. How tall are you? If your forearm is way forward of perpendicular at, or close to, contact then your cue tip will start going down. If you have a really long stroke you might shorten it up a bit, if you are tall and are running out of cue you might think of getting a longer cue, and finally, if you're just choking up on the cue for no apparent reason just move your hand back until your forearm is perpendicular to the ground at, or close to, contact. Hope this helps.

Take a look at my website for an analysis of this...it may help, or not. The Transcendental Pool section is serially written so you will have to go the the bottom of the pages for the next link.

http://www.hittcues.com/

 

[HittMan]

yet another country-boy, corn cob question

Actually, it turns out that for higher-velocity shots, the tip is in contact for a shorter time.

Hello Bob,
Can you imagine I have another question?
I'm going to assume you have seen high speed photography of the contact time you refer to here. How can it be that an accellerated cue might be in contact a shorter time? Would it not take longer for the cueball to reach a higher response velocity than a lower? OR...are we saying the difference in this interval is not relevant?

 

[FLICKit]

I haven't done any rotational transforms, either. Does that mean the discussion is invalid? Do you really want to see all the sines, cosines, and thetas?

All the nitpicking and minutiae aren't part of the point here. The issue kollegedave and I are discussing is whether or not extended follow through results in increased contact time. That's all. Nothing about verticality at impact, nothing about cue tips, nothing about pendulum swings, nothing about vector quantities, etc. We've taken the discussion to PM, so if anybody else wants to join in, send me a PM.

-djb

You're a bit all over the map. In order to properly address your posts, will have to refer to your other ones as well...

How would you account for the movement of the CB if acceleration is zero or near zero (which is what acceleration should be if you contact the CB when the forearm is vertical)?

You're way off on this one. You question how the CB moves if acceleration is zero. That's very ludicrous. The point has already been corrected, zero acceleration does not mean zero velocity (if you're being nitpicky, except in the one obvious situation, but on the whole it isn't zero velocity).

"zero (which is what acceleration should be if you contact the CB when the forearm is vertical)?"
Without having a sufficient baseline for the discussion, there are many responses to this. It could be true or very easily not true.

This also goes directly against your statement saying you didn't go into "nitpicking... nothing about verticality at impact, and nothing about pendulum swings".

Let's apply your line to this comment, see if you practice what you preach... prove it!

And just what does "accelerate through the CB" mean, anyway? Does the cue stick really "accelerate through the CB"?

You aren't very clear here. What are you suggesting happens, when you question whether the "cue stick really accelerates through the CB"?

Long follow through or short, I don't believe there's any effect whatsoever on spin. The only benefit of a follow through is an increase in consistency of stroke. Let the cue come to a natural stop.

Once again follow your own practice. Prove it.

As for your use of physics to demonstrate your point, I think you're missing some things. I'm going to have to pick apart this specific paragraph: "I do not think it is proper to accept that the acceleration of the cue is zero at the vertical point, because the motion is not frozen there. The cue has had its velocity increased from 0 at the end of the back swing to ever increasing values as it travels forward. Thus, the instant after vertical the cue should be travelling faster than it was at the instant it was at vertical. Therefore, acceleration has occurred."

OK... Since you don't have a baseline defined. Then I'll choose a baseline that will easily prove your statement wrong.

In a pendulum swing (which is possible), acceleration only occurs from the backswing to the bottom of the arch. At the bottom of the arch, then there is zero acceleration (note: not zero velocity). From the bottom of the arch all the way up through the forward swing, deceleration would occur. With a pendulum swing this would occur at a point virtually equal to the same distance as the backswing. This is Physics 101, if you really need that part proven, see

The Swing

First, acceleration, as you've said before, is delta vee, change in velocity. If there's no change, there's no acceleration. An object in motion can have zero acceleration. A car running 60 mph on cruise control is at zero acceleration (but its VELOCITY is still 60 mph) and it's definitely not frozen in motion.

Here you've at least remedied the error of the assumption from your earlier question.

"How would you account for the movement of the CB if acceleration is zero or near zero (which is what acceleration should be if you contact the CB when the forearm is vertical)? "

You recognize that there can be a velocity even with zero acceleration.

Then you get some sense but disprove your own earlier statement.

"I do not think it is proper to accept that the acceleration of the cue is zero at the vertical point, because the motion is not frozen there...

It starts from zero velocity, accelerates, reaches a top velocity, then negatively accelerates back to zero.

So what's really at work here? What causes the cue ball to move or spin if acceleration is zero and therefore force is zero?

Then you give the theories of momentum, which are proven. But you don't demonstrate that you can correlate those theories to the discussion at hand.

Explain in your words, how that applies to the discussion at hand. (Wouldn't be surprised if instead you avoided it, and tried to replace with some quip).

Where am I misleading anything? If velocity is constant, force is zero. Period. Sure, there's velocity and mass, nobody's disputing that. You're missing the point entirely.

You're saying if velocity is constant then force is zero and your question suggests that with zero force how does the cue ball move.

What I've said is that it still has a mass and a velocity. Refer back to your points on momentum and you'll see p=mv. Then apply the collision theory and you'll understand how the cue ball moves. Then add in the angular momentum discussion and you'll understand why it spins.

ALL players (not most players) have to accelerate the cue, otherwise it would never move.

That is flat out wrong. "ALL ... HAVE TO accelerate the cue" is flat out wrong.
Once again, I'll use a baseline which proves my point.
A player with a pendulum swing, simply has to pull their arm back x distance.

After the backswing, now, the player has to do nothing to accelerate the cue. The elimination of all muscles will allow the cue to accelerate from the force of gravity alone (not the player).

Acceleration usually continues until some distance past the point of contact? Are you sure about that?

Yes.

Once again I'll use a baseline which will prove my point.
Here, a pendulum swing wouldn't work.
But instead a swing from most any casual or beginner player.

Instead of an effortless swing, these players apply major effort in the swing. They swing the stick at a very rapid pace, and hit the cue ball hard. This style of swing would easily allow for acceleration after the point of contact.

Another example, would be a break shot. Many people not only utilize the force from their arm, but also add in power from their whole body (in general 100+ pounds). A cue ball that weights just a few ounces is gonna hold virtually no resistance to the arm and body weight of an adult. Thus acceleration can easily occur after the point of contact.


There is plenty more that can be said, and maybe I'll delve into at a later time...