Follow English????

[Jal]

I can draw & stop the CB & I am making some progress on making the CB deflect off the object ball &/or rail at predictable angles.

I am baffled when I try to make the CB follow the object ball. I hit above the equator of the CB, but the results are erratic. Help?!!

Most people find that draw is harder to control. You've received good advice, imo, but assuming you're actually hitting the cueball where you think you are, I think Jsp's recommendation to hit fairly high is very pertinent. Like he said, if you do, the only variable is cue speed, for the most part. You don't have to compensate as much for the slowing of the cueball on the way to the object ball.

There's another good reason to do this, or to use another strategy, which is to hit fairly close to center. It has to with how much spin gets rubbed off the cueball during impact. Quite a bit of it gets taken off (35%) when the cueball has a small spin/speed ratio. But it's a constant 35%, and therefore reliable. For very slow shots, this happens with tip offsets from zero to about 50% of maximum; for very fast shots, from zero to about 25% of maximum. We're assuming that the cueball's spin doesn't change much on the way to the object ball, or that this is the equivalent spin it has when it gets there.

With a lot of topspin, relatively little spin is removed during impact. So although the amount is more variable, the variations don't matter that much.

It's the intermediate spins that are hardest to predict. The amount that gets removed changes fairly rapidly with different initial spins in this region. On one shot, you might see 30%, but on the next, maybe only 10%. Since the follow (or draw) distance is proportional to the square of the post-impact spin rate, this variable has a significant effect.

A graph of how much spin is rubbed out as a function of tip offset can be found in this document (the second plot on page 4). It shows transfered spin to the object ball as a function of english, but the transfered spin is equal to the amount taken from the cueball. And it applies to follow/draw as well as to sidespin, if you allow for any changes on the way to the object ball.

Jim

 

[Tennesseejoe]

If you are getting draw but not follow, you may want to check to see if your cue ball is lighter than the object ball. Just use one of the other object balls as a cue ball and see if you can follow any easier. If you can follow better with the object ball then you may need a new cue ball. Many old cue balls are smaller thus weigh less due to wear over the years.

 

[Pinocchio]

Doomcue!!!!!!!!!!!

You have little or no idea of what you are talking about. Follow through is one of the most important components in achievement of gaining a good stroke. With force follow I would agree follow through is not necessary. If you don't understand follow through maybe you need lessons. I suggest Scott Lee maybe he could work with you an improve your game.
Pinocchio

 

[JLW]

I have no idea what the actual physics of this shot are, but this is what I do. And this is what I would advise you to do if you're having trouble with this shot. Keep your cue level, raise your (closed) bridge hand, hit the cb about a tip above center, and follow through.

 

[Pinocchio]

Tennesseejoe

Good point!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[Bob Jewett]

I have to disagree with Doom regarding follow through. True, the cueball needs to be rolling forward to follow after contacting the object ball, but the cueball can also have more spin than is required to just roll forward (essentially "peeling-out" on the felt)... A nice stroke (follow through implied) is required to get consistant cueball "peeling-out".

I am assuming that berlowmj's original question is concerning more than just natural follow....

In the vast majority of situations, it is pointless to have excess overspin on the cue ball. This is the topic of a current discussion over on the Billiards Digest forum and is covered in a chapter in Robert Byrne's "Advanced Technique" book. Contrary to what some have stated here, it is possible to get more follow on the cue ball than it has when it is rolling and with a level cue stick.

For the original poster, this advice:

Use a striped ball like the 10 for your cue ball. Clean it and place it so the stripe is horizontal. When you hit the "cue ball," your tip should be part way into the white cap, but you should actually make contact on the edge of the stripe. If you miscue when you try this, you need to learn to chalk. After you shoot, look at the ball and find the contact point, which will have a chalk mark on it. Did you hit where you intended?

Contrary to some of the above posts, it is not necessary to follow through to get pretty good follow on the cue ball. The follow-through is to promote accuracy of speed and contact point. It is much harder on your arm not to follow through. You should try to go through the ball about 6 inches, or the length of a dollar bill.

But from your question, it sounds like you are both very interested in the game and have some fundamental problems in your technique. If I were in your position, I would find an instructor for a one or two hour analysis of my mechanics.

 

[Rod]

I am baffled when I try to make the CB follow the object ball. I hit above the equator of the CB, but the results are erratic. Help?!!

berlowmj,

Assuming your hitting the c/b above center, distance from the o/b is the big factor. On longer shots follow is not a problem because the c/b takes on a natural follow roll. On close up shots (not enough time for natural roll) it takes a bit firmer hit with top to create that natural roll. Practice progressive shots near to far and you'll see what I mean.

I suspect your not hitting the c/b exactly where you think you are which is a stroke problem. Buy a training cue ball so you'll know where it is struck or possibly a striped ball placed in a horizontal position. When you can trust where you hit all progress starts from there.

Rod

 

[Jal]

Thank you for the link. I feel obligated to point out that Dr. Alciatore disregarded any vertical motion of the tip during its contact with the CB. This vertical motion has a significant effect on the angular momentum of the CB, and can be varied with grip hand placement, due to the pendulum like motion a shooter's arm as (s)he executes his/her stroke.

Dr. Alciatore also neglects cue elevation, and assumes linear cue motion parallel with the bed of the table, which is often not the case...

You're right that these things do have some effect, but I think "significant" may be pushing it a little.

For instance, you could look at the cue's vertical motion as either amplifying or reducing squirt, since it's really only the endmass that's at play with respect to this transverse motion. According to my understanding, and maybe you can show differently, it takes a heck of a lot of transverse speed to affect squirt in a significant way, and squirt doesn't have all that much of an effect on the generated spin.

I don't see that a cue elevation of a couple of degrees or so makes much difference either.

Another thing to consider is tip contact time and the ball's rotation during this period. To figure this out you have to be aware that the force vs time curve becomes highly non-symmentric at large tip offsets (fortunately in such a way as to make the initial tip offset pretty close to the "average" offset).

So you could drive yourself crazy trying to account for everything. In this case, I think Jsp's 0.4R is so close to the exact value that we can say that it's correct, for all practical purposes. But I certainly would welcome any insights or refinements you may have to offer on the physics of it. It's always nice to get these things as close to reality as possible.

Jim

 

[DoomCue]

You have little or no idea of what you are talking about. Follow through is one of the most important components in achievement of gaining a good stroke. With force follow I would agree follow through is not necessary. If you don't understand follow through maybe you need lessons. I suggest Scott Lee maybe he could work with you an improve your game.
Pinocchio

Actually, I think YOU have little or no idea of what I'm talking about. Nowhere have I said that follow through is not necessary, nor have I said that it isn't important. What I have said basically is that people are making erroneous assumptions concerning cause/effect relationships. Spin is not a result of the follow through, it's a result of the hit BEFORE the follow-through. The CB is already gone when the follow-through occurs. What part of that are you having trouble with?

I'm going to let you in on a little secret: I'm a BCA Recognized Instructor. Guess who was one of my instructors?

I'm not going to suggest you take pool lessons - I don't know how you shoot (but I'm going to guess that you need some as everybody does). I am, however, going to suggest you find someone who likes to do charity work. You need to spend some time with someone to go over reading comprehension. You may also want to pay a visit to the wedgie doctor - your panties are all in a bunch.

-djb

 

[acedotcom]

I can draw & stop the CB & I am making some progress on making the CB deflect off the object ball &/or rail at predictable angles.

I am baffled when I try to make the CB follow the object ball. I hit above the equator of the CB, but the results are erratic. Help?!!

Nice thread, berlowmj. I have trouble with force follow. When I was a kid playing straight pool, I could drive the cb thru a rack with follow. I can't get that kind of action anymore. There are more than enough ideas here for me to apply to my own problem.

BTW, I might be wrong, but, strictly speaking, I don't think "follow" is english, though you can combine it with right or left english.

 

[FLICKit]

I think slow-motion photography proves that follow through doesn't really matter - ...

I agree with you that a nice stroke in general has a nice follow through, but the follow through is a consequence of the stroke, and has no bearing on the CB. Again, the CB only cares about what happens at time of contact - what happens before or after doesn't matter to the CB.

-djb

I am going to SUGGEST something which many of you may feel is heresy. I have seen the slow-motion photography that many of you are referring to. In its details, I SUGGEST that it is not of sufficient enough magnification to clearly define the results of follow through or acceleration or deceleration... at the moment of impact.

It shows that there is a noticable stopping motion of the cue at the point of impact. Then follows the implication that says thus the type of stroke has no impact. But this may not necessarily be true.

It will take higher levels of magnification to prove/disprove this theory.

There are a number of details which aren't being displayed clearly enough to make a definitive statement.

 

[cuetechasaurus]

To the first poster- try this, it will help.

Set up a straight in shot, it doesn't have to be long. Stand behind the shot like you normally do before you get down to shoot. While still standing, place your bridge hand down at the cueball, and make sure your tip is in the middle of the cueball. This is called the halfway point. Now, lower yourself slowly into shooting position, and as you lower your upper body, keep your arm still so that it lowers the back end of the cue along with you. Focus on keeping your tip along the vertical axis of the cueball, and what will happen, is as you are lowering yourself, your tip will start to rise to the top of the cueball. Your arm is also pretty level when you finally get down on the shot. The good thing about this position, is with the technique you used getting down on the shot, your tip cannot dive down and hit center or below, you are forced to hit follow. You will have a pretty level stroke like this. Keep shooting shots like this, and the cueball will get plenty of follow. If you are having trouble with it, this is a great way to learn. Hope this helps.

 

[Rasta]

You're right that these things do have some effect, but I think "significant" may be pushing it a little.

I think the word significant is apt in this case. The vertical motion of the cue tip applies torque at a distance of 1*R from the axis of rotation. That means only about 2/5 the force is necessary to apply the same change in angular momentum of the cueball as hitting the cueball with a level cue and a grip hand placement that effectively eliminates vertical cue tip motion.

For instance, you could look at the cue's vertical motion as either amplifying or reducing squirt, since it's really only the endmass that's at play with respect to this transverse motion. According to my understanding, and maybe you can show differently, it takes a heck of a lot of transverse speed to affect squirt in a significant way, and squirt doesn't have all that much of an effect on the generated spin.

I'm not sure I am correctly understanding your usage of the term squirt in this context.

I don't see that a cue elevation of a couple of degrees or so makes much difference either.

Since it is the distance from the radius on a line orthogonal (perpendicular) to the velocity of the cue that is relevant for measuring torque, the angle of elevation must be taken into consideration. An elevated cue will decrease follow compared to the same shot and point of contact on the CB with a level cue. An elevated cue will increase draw compared to a level cue, all else equal.


Cue elevation also affects how much force is applied to moving the CB along the playing surface (linear motion). The closer to level the cue is, the less significant this consideration becomes. A ten degree angle of cue elevation decreases the force on the CB that is parallel to the playing surface by only about 1.5%. However, the scale is not linear. If the angle of elevation is increased to 20 degrees, the reduction is about 6% from level. If increased to 30 degrees, the force is reduced by over 13%. A 30% elevation is neither optimum (for most shots) nor unusual.

Another thing to consider is tip contact time and the ball's rotation during this period. To figure this out you have to be aware that the force vs time curve becomes highly non-symmentric at large tip offsets (fortunately in such a way as to make the initial tip offset pretty close to the "average" offset).

So you could drive yourself crazy trying to account for everything. In this case, I think Jsp's 0.4R is so close to the exact value that we can say that it's correct, for all practical purposes. But I certainly would welcome any insights or refinements you may have to offer on the physics of it. It's always nice to get these things as close to reality as possible.

Jim

I agree that there are many variables. That was actually my point. Dr. Alciatore's 0.4*R figure is a special case, and not a general case. It will work great whenever the cue is nearly level, and the grip hand is placed in a manner that minimizes vertical motion of the cue tip. When these two conditions aren't met, however, the number loses it's meaning.

I remember back when my University Physics professor "explained" how upon impact, billiard balls moved along orthogonal paths. Anyone who has ever played the game knows that is only true if the two balls are not rotating at the time of impact, a special case. The fact is, pool is usually not played within the confines of these special cases. Most players add some sort of spin to the cueball to affect the results of it impacting with an OB or a rail. Similarly, the cue is often not held level while stroking.

So, while it is a nice rule of thumb that hitting the cueball about 2/5 of the radius above the equator will give the CB a natural roll right from the start, it is important to know that this rule is not absolute. It is also useful to know what different things can affect how the cueball spins, and how that spin affects play.

Good Rolls,
Rasta

 

[FLICKit]

Rasta is accurate. Cue elevation does have impact on results.

 

[Bob Jewett]

... There are a number of details which aren't being displayed clearly enough to make a definitive statement.

I'm not sure which details need to be seen, but the main result is that the tip is on the ball for only about 1/4-inch of travel (depending on speed), and then the ball has left the tip. The physical arguments about the usefulness or uselessness of acceleration at the moment of impact are not changed by what has been seen so far on the high-speed videos, and I can't think of a new test that would add to what we know so far.

Can you be more specific?

 

[Jal]

I think the word significant is apt in this case. The vertical motion of the cue tip applies torque at a distance of 1*R from the axis of rotation. That means only about 2/5 the force is necessary to apply the same change in angular momentum of the cueball as hitting the cueball with a level cue and a grip hand placement that effectively eliminates vertical cue tip motion.

I don't think this is true Rasta. The vertical motion has only the endmass behind it, as I understand it. It's not equivalent to the entire mass of the cue, or more to the point, the component of the cue's momentum which is tangential to the surface.

It's been a while since I did the calculations, but look at it this way, if you will. At some shot speed, a tip offset of .4R will produce a certain amount of spin and squirt if the cue is stroked straight ahead. If instead, you swing the tip out by rotating the cue during your stroke, you'll reduce the amount of impulse (force X time) the cueball will have to exert to push the stick aside as it develops spin. So you'll reduce the squirt accordingly. (I'm using squirt here to mean not just sideways deflection but in any direction). My calculations showed that you really have to get the tip moving sideways (or upwards, downwards) by a fairly large fraction of its forward speed to reduce squirt by, say, 50%. Even if you could reduce it 100%, you would see only a very small increase in the spin rate. So I really don't think this gains you much, but I urge you to do the calculations to see if I'm right.

Cue elevation also affects how much force is applied to moving the CB along the playing surface (linear motion). The closer to level the cue is, the less significant this consideration becomes. A ten degree angle of cue elevation decreases the force on the CB that is parallel to the playing surface by only about 1.5%. However, the scale is not linear. If the angle of elevation is increased to 20 degrees, the reduction is about 6% from level. If increased to 30 degrees, the force is reduced by over 13%. A 30% elevation is neither optimum (for most shots) nor unusual.

Yes, agreed, sort of. With increasing elevation, the cueball is prevented from taking off as rapidly, so you get some boost in force (impulse) from this. But you also lose horizontal velocity, as you point out. I took it for granted that we were talking about normal elevations of only a few degrees.

I agree that there are many variables. That was actually my point. Dr. Alciatore's 0.4*R figure is a special case, and not a general case. It will work great whenever the cue is nearly level, and the grip hand is placed in a manner that minimizes vertical motion of the cue tip. When these two conditions aren't met, however, the number loses it's meaning.

As per above, I don't think it loses its meaning. Most shots are done with a nearly level cue, particularly follow shots.

I remember back when my University Physics professor "explained" how upon impact, billiard balls moved along orthogonal paths. Anyone who has ever played the game knows that is only true if the two balls are not rotating at the time of impact, a special case.

It's not exactly true even then. Throw and effects from inelasticity are always at play. One interesting tidbit that I recently learned is that the object ball traverses an "S" shaped path during impact.

Jim

 

[3kushn]

You're not following through.

Ditto

May not be high enough. Pro English is much higher than most realize.

 

[Rasta]

I don't think this is true Rasta. The vertical motion has only the endmass behind it, as I understand it. It's not equivalent to the entire mass of the cue, or more to the point, the component of the cue's momentum which is tangential to the surface.

It's been a while since I did the calculations, but look at it this way, if you will. At some shot speed, a tip offset of .4R will produce a certain amount of spin and squirt if the cue is stroked straight ahead. If instead, you swing the tip out by rotating the cue during your stroke, you'll reduce the amount of impulse (force X time) the cueball will have to exert to push the stick aside as it develops spin. So you'll reduce the squirt accordingly. (I'm using squirt here to mean not just sideways deflection but in any direction). My calculations showed that you really have to get the tip moving sideways (or upwards, downwards) by a fairly large fraction of its forward speed to reduce squirt by, say, 50%. Even if you could reduce it 100%, you would see only a very small increase in the spin rate. So I really don't think this gains you much, but I urge you to do the calculations to see if I'm right.

If I am understanding you correctly ( I may not be.), then we are talking about two different mechanisms causing vertical motion of the tip. I am talking about how placing the grip hand way back on the cue can cause the tip to rise during contact with the cue ball, since the grip arm has not "bottomed out" in the pendulum motion of the stroke. (Conversely, holding the grip area nearest the forearm of the cue can cause the tip to move downward during contact with the cue ball, since the arm has past the "bottom" of the pendulum swing.)

This is different from the end mass/ squirt issue, I think, since the motion occurs even without interaction with the CB.

I've not modeled it, but this effect was one of the things a player much better than myself showed me. When I began changing up my grip position, I immediately saw a big difference in my draw. I'll be the first to admit, however, that first hand anecdotal evidence is among the worst kind.

Yes, agreed, sort of. With increasing elevation, the cueball is prevented from taking off as rapidly, so you get some boost in force (impulse) from this. But you also lose horizontal velocity, as you point out. I took it for granted that we were talking about normal elevations of only a few degrees.

As per above, I don't think it loses its meaning. Most shots are done with a nearly level cue, particularly follow shots.

Ideally this is true, but I've been jacked up on a shot more times than I can count. Either a ball is in the way, or the tables too close to a wall or chair, or any other reason.

It's not exactly true even then. Throw and effects from inelasticity are always at play. One interesting tidbit that I recently learned is that the object ball traverses an "S" shaped path during impact.

Jim

I agree, it's not exactly true even then. I was just trying to illustrate that there are many variables, and we are best served as players when we know when those variables can be disregarded, and when ignoring them can be the difference between making or missing the shot or shape.

Having said that, you better believe I've tucked that "0.4*R" bit of info back for future reference on the table.

Good Rolls,
Rasta

 

[Jal]

If I am understanding you correctly ( I may not be.), then we are talking about two different mechanisms causing vertical motion of the tip. I am talking about how placing the grip hand way back on the cue can cause the tip to rise during contact with the cue ball, since the grip arm has not "bottomed out" in the pendulum motion of the stroke. (Conversely, holding the grip area nearest the forearm of the cue can cause the tip to move downward during contact with the cue ball, since the arm has past the "bottom" of the pendulum swing.)

This is different from the end mass/ squirt issue, I think, since the motion occurs even without interaction with the CB.

Sorry Rasta, I was mixing horizontal effects with vertical effects in that paragraph, because the mechanisms are the same, only the direction changes. I think we do understand each other and I agree that the vertical motion you've been refering to has a different cause (pendulum arc) than the one I've been refering to (cueball rotation pushing the tip further off-center).

But I see them as connected for the purpose of understanding what effect the motion you're refering to has on the cueball. At large tip offsets, such as .4R, I don't believe you can get the tip moving away from center via your motion (vertical swoop) fast enough to keep up with the ball rotation. But you do get some vertical squirt relief because you're doing with your stroke what the cueball's rotation does anyway, but at the cost of squirt. And since variations in squirt make little difference to the ball's acquired spin, it seems unlikely that the swooping makes any significant difference to it. At small tip offsets it should have a much greater effect.

I've not modeled it, but this effect was one of the things a player much better than myself showed me. When I began changing up my grip position, I immediately saw a big difference in my draw.

Since I believe what I said above, I suspect that what happened is that you began hitting lower on the cueball.

I'll admit that I'm not absoulutely sure of any of this, but am more or less persuaded by the argument. Some experimentation would help.

Jim

 

[FLICKit]

I'm not sure which details need to be seen, but the main result is that the tip is on the ball for only about 1/4-inch of travel (depending on speed), and then the ball has left the tip. The physical arguments about the usefulness or uselessness of acceleration at the moment of impact are not changed by what has been seen so far on the high-speed videos, and I can't think of a new test that would add to what we know so far.

Can you be more specific?

OK Bob, here we go. You and I had a bit of a tussle about this not too long ago, but it was related to draw instead.

In that discussion you pointed out that the stick basically stops at the point of impact. I disagreed, but the high speed video clearly showed basically a stopping motion and a very very short moment of impact between the stick and the cue ball. So, I'll admit to that and concur, and I've learned something from it. I think deep down, we're both similar in that we'd rather get to accurate information rather than just bravado of having to appear "right".

Now first of all, I have a very "strong opinion" that stroke matters, and matters quite a bit. I also believe that many expert players will agree with that "premise" just from their personal experience. The cue ball can be made to act quite differently depending on the type of stroke imparted.
Also I "suggest" that the most important factor relating to draw and follow is SPIN. If there is ample reverse spin on the cue ball after contacting the object ball, then it WILL draw back. And, if there is ample top spin on the cue ball after contact, then it WILL roll forward. Of course must also account for top spin generated from the friction between the cue ball and the felt. -- Excluding all other unnecessary factors -- And so, the type of stroke can impact the amount of spin imparted.

I also know that you, and a group of teachers believe that the high speed videos conclusively prove that stroke doesn't matter. And you infer that this is conclusive evidence based on the essentially stopping motion of the cue and the relatively small moment of impact between the cue ball and the stick.

Accepting your premise, it seemed reasonable at first and for awhile. After a period of time, I then came to the realization and surmised that the videos that I saw need surprisingly much more detail in order to be conclusive.

-------------------------------------------------------------------
Obviously we know that tip compression and tip decompression are a part of what occurs. Unfortunately this adds additional complexities which I'm not sure that we can just rule out.

Some factors need to be visible and distinguishable, or even better definable and measurable.

So, we have cue speed at the moment before impact. And the type of stroke (accelerated, decelerated, ...) Would be useful if visible/measurable here.

Then we'd need to know tip compression and its rate. Would also be useful if visible/measurable. And would need to know if type of stroke (accel., decel...) had any impact on the compression. Is the compression rate faster/slower/no difference? Is the compression deeper/shorter/no difference? Possibly even does it remain compressed for a longer/shorter/no difference period of time before it starts decompressing?

Might even need to know what's happening to the stick while the tip compression is occuring:
Change in speed of the stick during the tip compression, during the tip decompression, ...
Also flex factors of the stick (is it bending, how much, how fast, how long?) Is this any different depending on the type of stroke?

Gonna assume that all the factors of force and mass exerted (ie from the human) on the stick can be consistent and thus irrelevant.

All the information that we gathered during "compression" might also need to be gathered during "DEcompression", unless can be positive that contact is over and thus decompression has no relevancy...

Lastly, at what point is the impact over? During the tip compression, tip decompression, after tip decompression,...? Does the stick speed actually reach 0 or some speed very close to 0? And what is happening to the stick in this time period? And is there any change in this depending on initial stroke?

Obviously the stick then begins to accelerate in order to go from 0 back to something close to its original speed before impact for either a long distance (follow through), short distance or whatever... This part is what derives those conclusions that the stroke has no impact. And that the moment of impact is so short that stroke impact is not relevant.

I know this might sound too exhaustive, and maybe even too extreme for some. But, I believe that this is what it's going to take in order to prove it. Without that level of clarity, then I understand that people will come to conclusions based on what they have, which may be all we can do at this time.

There may be more to look through for more definitive results...
On the surface, one of the things I notice from Dave's examples is that his followthrough strokes produce more dramatic results. He's getting more draw from his followthrough strokes than his punch strokes.