i apologize for the length of this post, but i'm trying to exposit, as clearly as i can, a significant point which, as far as i know, has been severely mistreated in the pool world.
i have heard too many times from pool players, and i have read too many times in the pool literature, that you can achieve all the cue ball action you need with merely one stroke. so i've heard, and so i've read, it does not matter whether i use a long stroke or a short stroke, whether i have lots of follow-through or none at all, my cue ball will react in the same way. all i can do with my stroke is provide a linear speed and a contact point for my tip on the ball. and in doing so, i can achieve all possible combinations of linear and angular velocities. i don't believe this.
the justification of this "one stroke is all you need" thesis is usually made with two arguments. the first goes something like this: after the ball leaves your tip, the ball does not care if your tip follows through or not. no doubt, any reasonable person will agree with this. the problem with this argument, however, is that it implicitly assumes that there is no significant difference between the event of your tip first contacting the ball and the separate event of the ball leaving your tip. this brings us to the second argument usually made: the jacksonville experiments "demonstrated" that there is no significant difference between these two events. let's explore this a little deeper.
what the jacksonville experiments actually demonstrated (in relation to this discussion) was this: for the limited strokes tested, the time between these two events--let's call this the dwell time--was very small, about a millisecond. (i should mention that the jacksonville experiments were a great milestone in advancing our understanding. however, no experiment should yield conclusions thought to be definitive; advancement in any science involves constant constructive criticism of previous experiments leading to ever new, better experiments.) first, let's consider the first clause. the strokes tested must have been very limited. in "billiards digest" shamos wrote, "no matter how anyone stroked, the best we could do was to have the cue stick move at constant speed for the last few inches before it hits the ball. in fact, unless a very good stroke is used, the stick actually decelerates on the way in." why couldn't anyone produce a stroke that was accelerating at contact? there's no reason to think that this is physically impossible. in fact, i contend that top three-cushion players do this all the time. perhaps during the experiments, only perfect pendulum strokes were used. (for what it's worth, three-cushion players employ such pendulum strokes for only a minority of shots.) note that no elite players were used to produce the strokes tested.
let's now explore the second clause, namely that the dwell time is very small. this finding has been used to dismiss many hypotheses concerning what contributes to ball action (e.g. grip, follow-through, etc.). since only non-accelerating (or decelerating) strokes were tested, such dismissals are at best premature. to see why, we need to understand what happens during this very small dwell time.
if the tip is not accelerating at contact, we can view the contact between the tip and ball as a collision between two objects. when a non-accelerating object hits a stationary object, energy is transferred from the former to the latter. (if the kinetic energy is conserved, such a collision is said to be elastic. see http://en.wikipedia.org/wiki/Elastic_collision for a nice explanation.) what happens during the collision is very, very complicated. we need to know how the objects deform under stress, how the stress propagates, etc. to simplify all this, physicists use the concept of an impulse. an impulse is defined as the change in momentum of an object when a large force is applied over a very brief period of time. we can now say that, at best, the jacksonville experiments showed what the dwell time was for "impulsive strokes" (i.e. non-accelerating strokes). but what happens when the tip accelerates as it hits the ball? surely this is possible.
acceleration implies a force. when a force acts upon an object over a distance, a transfer of energy takes place. physicists refer to this transfer of energy as work. (see http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html for a good explanation.) i am contending that when a player produces an accelerating stroke, work is being done to the ball. if this is indeed happening, there should be a measurable dwell distance--the distance over which the ball travels while still in contact with the tip. (note that referring to the jacksonville experiments here is useless as no accelerating strokes were tested.) for these "working strokes" (i.e. accelerating strokes) it is the dwell distance, not the dwell time, that is relevant. in fact, the dwell time for working strokes may indeed be roughly the same as the dwell time for impulsive strokes. however, the dwell distance will be significantly greater for working strokes. in a working stroke, the tip is pushing the ball over a longer distance, but since the tip is accelerating, more distance will be covered in the same time interval. moreover, the deformations of the tip and ball is different for working strokes than it is for impulsive strokes. for working strokes, since the tip is accelerating, such compressions and decompressions may occur more quickly than for impulsive strokes. this is widely known for the collision between the strings of a tennis racket and a tennis ball. the dwell time is roughly five milliseconds for nearly all types of tennis strokes. but the dwell distance is much greater for those strokes where the racket accelerates through the ball.
if i am correct, that is, if top players routinely employ working strokes, then what has passed as conventional wisdom in poolrooms and in the pool literature must be reconsidered. it is my belief that a significant factor as to why top pool players are far more consistent than amateurs is that they "work" the cue ball a lot more; that is an accelerating stroke is more consistent than a non-accelerating one. furthermore, top three-cushion players are able to achieve the wide range of spin-to-speed ratios (at many varying speeds) that they do since they employ many different strokes, each with differing amounts of work, and some with only impulse.
i look forward to reading other thoughts on this.
william hanisch
i have heard too many times from pool players, and i have read too many times in the pool literature, that you can achieve all the cue ball action you need with merely one stroke. so i've heard, and so i've read, it does not matter whether i use a long stroke or a short stroke, whether i have lots of follow-through or none at all, my cue ball will react in the same way. all i can do with my stroke is provide a linear speed and a contact point for my tip on the ball. and in doing so, i can achieve all possible combinations of linear and angular velocities. i don't believe this.
the justification of this "one stroke is all you need" thesis is usually made with two arguments. the first goes something like this: after the ball leaves your tip, the ball does not care if your tip follows through or not. no doubt, any reasonable person will agree with this. the problem with this argument, however, is that it implicitly assumes that there is no significant difference between the event of your tip first contacting the ball and the separate event of the ball leaving your tip. this brings us to the second argument usually made: the jacksonville experiments "demonstrated" that there is no significant difference between these two events. let's explore this a little deeper.
what the jacksonville experiments actually demonstrated (in relation to this discussion) was this: for the limited strokes tested, the time between these two events--let's call this the dwell time--was very small, about a millisecond. (i should mention that the jacksonville experiments were a great milestone in advancing our understanding. however, no experiment should yield conclusions thought to be definitive; advancement in any science involves constant constructive criticism of previous experiments leading to ever new, better experiments.) first, let's consider the first clause. the strokes tested must have been very limited. in "billiards digest" shamos wrote, "no matter how anyone stroked, the best we could do was to have the cue stick move at constant speed for the last few inches before it hits the ball. in fact, unless a very good stroke is used, the stick actually decelerates on the way in." why couldn't anyone produce a stroke that was accelerating at contact? there's no reason to think that this is physically impossible. in fact, i contend that top three-cushion players do this all the time. perhaps during the experiments, only perfect pendulum strokes were used. (for what it's worth, three-cushion players employ such pendulum strokes for only a minority of shots.) note that no elite players were used to produce the strokes tested.
let's now explore the second clause, namely that the dwell time is very small. this finding has been used to dismiss many hypotheses concerning what contributes to ball action (e.g. grip, follow-through, etc.). since only non-accelerating (or decelerating) strokes were tested, such dismissals are at best premature. to see why, we need to understand what happens during this very small dwell time.
if the tip is not accelerating at contact, we can view the contact between the tip and ball as a collision between two objects. when a non-accelerating object hits a stationary object, energy is transferred from the former to the latter. (if the kinetic energy is conserved, such a collision is said to be elastic. see http://en.wikipedia.org/wiki/Elastic_collision for a nice explanation.) what happens during the collision is very, very complicated. we need to know how the objects deform under stress, how the stress propagates, etc. to simplify all this, physicists use the concept of an impulse. an impulse is defined as the change in momentum of an object when a large force is applied over a very brief period of time. we can now say that, at best, the jacksonville experiments showed what the dwell time was for "impulsive strokes" (i.e. non-accelerating strokes). but what happens when the tip accelerates as it hits the ball? surely this is possible.
acceleration implies a force. when a force acts upon an object over a distance, a transfer of energy takes place. physicists refer to this transfer of energy as work. (see http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html for a good explanation.) i am contending that when a player produces an accelerating stroke, work is being done to the ball. if this is indeed happening, there should be a measurable dwell distance--the distance over which the ball travels while still in contact with the tip. (note that referring to the jacksonville experiments here is useless as no accelerating strokes were tested.) for these "working strokes" (i.e. accelerating strokes) it is the dwell distance, not the dwell time, that is relevant. in fact, the dwell time for working strokes may indeed be roughly the same as the dwell time for impulsive strokes. however, the dwell distance will be significantly greater for working strokes. in a working stroke, the tip is pushing the ball over a longer distance, but since the tip is accelerating, more distance will be covered in the same time interval. moreover, the deformations of the tip and ball is different for working strokes than it is for impulsive strokes. for working strokes, since the tip is accelerating, such compressions and decompressions may occur more quickly than for impulsive strokes. this is widely known for the collision between the strings of a tennis racket and a tennis ball. the dwell time is roughly five milliseconds for nearly all types of tennis strokes. but the dwell distance is much greater for those strokes where the racket accelerates through the ball.
if i am correct, that is, if top players routinely employ working strokes, then what has passed as conventional wisdom in poolrooms and in the pool literature must be reconsidered. it is my belief that a significant factor as to why top pool players are far more consistent than amateurs is that they "work" the cue ball a lot more; that is an accelerating stroke is more consistent than a non-accelerating one. furthermore, top three-cushion players are able to achieve the wide range of spin-to-speed ratios (at many varying speeds) that they do since they employ many different strokes, each with differing amounts of work, and some with only impulse.
i look forward to reading other thoughts on this.
william hanisch
