pause before pulling the trigger?

[Patrick Johnson]

...if your thesis was true, then the car could go from zero to 60 mph without achieving ANY speed for ANY length of time.

I believe that's exactly what he's saying. The car doesn't spend any time at any particular speed because its speed is always changing.

Here's another analogy (in case this isn't already confusing enough): A point on the equator of a CB spinning in place moves into and out of one tangent line after another as it circles the ball. All these tangent lines are perpendicular to a radius of the CB and the point is always moving perpendicular to a radius of the CB, yet it never moves along any particular tangent line for any length of time because that would = going straight, which it never does.

pj
chgo

 

[Franky]

Hehe. Newtonian physics basics are fun Bob! Explain all of it please.

Next topic by Bob: The Heisenberg Uncertainty Principle.

 

[Bob Jewett]

Hehe. Newtonian physics basics are fun Bob! Explain all of it please....

I would but there is not room for it on the margin of this page.

 

[Cephalus]

There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this. The arguement seems to be about the definition of a pause.

The definition most applicable to this scenarios is this: a time interval during which there is a temporary cessation of something.

Which leads us to this:
time interval: a definite length of time marked off by two instants

Thus, in order for there to be a pause, there must, by definition, be at least two instants at which the velocity of the ball is at 0.

If you graphed the ball's velocity vs time graph, it would be a simple parabola (this should be obvious, if anyone disagrees I can prove this quite easily). The point at which the velocity is 0 would be the low point of the parabola - and the only instant at which the velocity was 0. Therefore, the ball is not at velocity 0 for a time interval, therefore there is no pause.

 

[mikepage]

There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this. The arguement seems to be about the definition of a pause.

The definition most applicable to this scenarios is this: a time interval during which there is a temporary cessation of something.

Which leads us to this:
time interval: a definite length of time marked off by two instants

Thus, in order for there to be a pause, there must, by definition, be at least two instants at which the velocity of the ball is at 0.

If you graphed the ball's velocity vs time graph, it would be a simple parabola (this should be obvious, if anyone disagrees I can prove this quite easily). The point at which the velocity is 0 would be the low point of the parabola - and the only instant at which the velocity was 0. Therefore, the ball is not at velocity 0 for a time interval, therefore there is no pause.

Yes, and to bring it back to the pool stroke, look at this video starting at 4:00

http://www.youtube.com/watch?v=y0hs4Ka1xMA

The curves you see are the position of the tip (along the horizontal axis) versus time (on the vertical axis). A pause would be represented by a straight vertical line of some length. The pause appears in red at almost 7 minutes.

 

[td873]

Yes, and to bring it back to the pool stroke, look at this video starting at 4:00

http://www.youtube.com/watch?v=y0hs4Ka1xMA

The curves you see are the position of the tip (along the horizontal axis) versus time (on the vertical axis). A pause would be represented by a straight vertical line of some length. The pause appears in red at almost 7 minutes.

I particuarly like your analysis of the "ramifcations" of the extended pause - including two transitions of simply motions, shooter decision to GO, developing a hitch, and hiding a non-uniform backstroke. Despite the fact that the pause is taught for certain players, these "side effects" are seldom mentioned. The point being: it takes diligence and decication to properly integrate the extended pause in your stroke.

I also agree that a slower backstroke will remedy the slow shifting eyes. However, as you allude in your video, it is not always a function of the eyes moving too slow. Rather it may simply be the back swing being too fast. IMO, this approach will solve 80-90% of eye pattern related stroke problems.

Overall, your video is a great analysis of the stroke. Great job (greenies for ya!)

-td

[I thought the Point of No Return "PONR" was PORN the first time I saw it ]

 

[av84fun]

I believe that's exactly what he's saying. The car doesn't spend any time at any particular speed because its speed is always changing.

I haven't read Bob's repy yet and even though I am a reasonably well educated person, I am about ready to throw in the towel on this one becuase the odds favor those with serious education in physics trumping the logic that I bring to this discussion.

Clearly, not everything in science makes sense to the logical mind and I stipulate to that.

But here is my response to your remark.

If a car spend zero time at any particular speed then it can be proven that the car did not move at all.

If what you are saying is true, then no one could ever be convicted of speeding by evidence furnished by a radar gun. It it can be proven scientifically that the car in question spent ZERO time at the speed indicated by the radar gun...then the gun would be in error and the case would have to be dismissed.

Maybe speeders should be represented in court by physicists and not lawyers!!! (-:

Regards,
Jim

 

[av84fun]

There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this.

Resectfully, I disagree. That is exactly what Bob and a few others have been disputing....they argue that there is no stop for any fraction of a millisecond (or words to that effect) posted by Bob.

Regards,
Jim

 

[mikepage]

There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this.

Resectfully, I disagree. That is exactly what Bob and a few others have been disputing....they argue that there is no stop for any fraction of a millisecond (or words to that effect) posted by Bob.

Regards,
Jim

Jim, Ceplalus stated Bob's and position correctly. It is you that doesn't understand the distinction here.

 

[av84fun]

Hello Mike. I see that you posted the video to utube and I assume that you are the commentator. I found it to be an excellent presentation. Thanks for posting it.

However, there are two issues with which I disagree. One...the pause. You argue against it while being carefull to mention that a number of top teachers and world champion players use it. Those teachers/pro have written extensively about the benefits of the pause that would oppose your views to the contrary.

All that suggests to me is that the pause is a personal choice and cannot be argued to be be either good or bad for all players.

One other issue I have is with your comment on the "practice" or "warm up" strokes. You suggest...not in these exact words becuase I didn't memorize them...but words to the effect that one purpose of the warm up strokes is to guage the speed of the upcomming final forward stroke.

In my observation, the velocity of the warm up strokes is virtually idendical in almost all circumstances regardless of the speed the player wishes to achieve with the cue ball.

Finally, let me ask if the "S" curves you depicted at around the 4 minute mark were drawn graphics or actual plots from some scientific instrument.

Don't get me wrong...I think they cureves were highly useful in depicting what happens during the stroke. The only issue I have is whether the curves were a result of an instrument plot that would have shown zero motion at the instant of the reversal from back to forward stroke...or whether the curves were just draw by a human being to depict the general idea without (quite correctly) attempting to prove or disprove a tiny momentary pause...which is irrelevant to the discussion of the pool stroke (but an interesting topic as indicated by the numerous posts on that sub-thread).

THANKS!

Jim

 

[mikepage]

Hello Mike. I see that you posted the video to utube and I assume that you are the commentator. I found it to be an excellent presentation. Thanks for posting it.

However, there are two issues with which I disagree. One...the pause. You argue against it while being carefull to mention that a number of top teachers and world champion players use it. Those teachers/pro have written extensively about the benefits of the pause that would oppose your views to the contrary.

Fair enough. I respect those people and their views.

All that suggests to me is that the pause is a personal choice and cannot be argued to be be either good or bad for all players.

I'll accept this.

One other issue I have is with your comment on the "practice" or "warm up" strokes. You suggest...not in these exact words becuase I didn't memorize them...but words to the effect that one purpose of the warm up strokes is to guage the speed of the upcomming final forward stroke.

In my observation, the velocity of the warm up strokes is virtually idendical in almost all circumstances regardless of the speed the player wishes to achieve with the cue ball.

I think I might appeal to your "personal choice" comment above.

Finally, let me ask if the "S" curves you depicted at around the 4 minute mark were drawn graphics or actual plots from some scientific instrument.

[...]

just illustrating an idea.

 

[av84fun]

Jim, Ceplalus stated Bob's and position correctly. It is you that doesn't understand the distinction here.

That is very possibly correct Mike. But Ceplalus wrote:

"Originally Posted by Cephalus
There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this."

And Bob wrote:

Well, no, they don't state any such thing. Physics is my day job, so I suspect I'm right on this one. A ball thrown straight up has no pause at the top. A child on a swing has no pause at the ends of the arc. And many, many players have no pause on their backswings. You can say they do, but technically, and in physics, you would be wrong.


Quote:
Originally Posted by Snorks
Just a second.. Now, I am not in physics, but at some point a ball tossed up in the air must 'stop' moving up, and 'start' moving down. If this is not a pause, what is it called (for the record I have no idea)? Seems to me this millisecond (or even less then a millisecond), has to be a stop or pause. Same thing would apply to the pool stroke in my opinion. ...

"The ball is not motionless for a millisecond or a microsecond or even a billionth of a billionth of second. The length of time that it is motionless is zero. That is not a pause."

So, Ceplalus states that a ball thrown exactly vertically reaches a point where it is "not moving in either direction." and I suggest that it is irrefutable, therefore, that he believes that ball has "STOPPED" which is undoubtedly a synonym for being motionless.

Yet Bob states that the ball is NOT "motionless" for even a billionth of a billionth of a second.

I am sure you can see why those comments...as written...are fundamentally contradictory.

Now...FINALLY (for me) let me say that I read a paper once suggesting why the universe...which is said to be BOTH infinate (of course, meaning that it has no outer boundaries) is also "constantly expanding."

Well, to "expand" there must be a boundary from which to increase in size.

Admittedly, I read every word in the paper...all of which was written in English which is my native tongue but I didn't understand a word of it.

But, if science says that a body can be "motionless" while, nevertheless being in motion...so be it. I surrender after this one last comment.

I have posted a link to a science-oriented site that depicted the ball reaching the speed of zero at the top of its one dimensional upward travel before descending.

I have not seen anyone post a link to any authority that holds that the ball, to the contrary is in constant motion.

I will now turn my attention back to practicing three rail kicks!!! (-:

Regards,

Jim

 

[av84fun]

Thanks Mike.
(-:

 

[Mark Avlon]

i see this a lot with allison fisher and karen corr. they would take they practice stroke and on the final pull-back, they would just pause for 2-3 seconds before they forward stroked and shot the ball. it seems to make them really consistent in their play.

i'm wondering if it would be a good idea to try to adopt this method of play.

The change between the backswing and the forward stroke is simply a transition in the direction of the cue's motion. There is nothing magical about the length of time for this transition. The goal is simply to bring the cue back and then forward along the line of aim. Everyone is unique, and as long as the player can accomplish this, it doesn't matter how long the transition is, providing that it doesn't interfere with their eye pattern. This transition can be immediate, or there can be up to a several second pause between the motions.

A key factor in keeping the cue on the line of aim during this transition is to have a smooth stop to the backswing, and a smooth start of the forward stroke. Quick stops and starts can easily throw the cue off the line of aim.

Experiment and see what works best for you. Once you find what works, be consistent with it.

 

[mikepage]

That is very possibly correct Mike. But Ceplalus wrote:

"Originally Posted by Cephalus
There is obviously a point in time where a ball thrown straight up and allowed to fall back down is not moving in either direction. No one is disputing this."

And Bob wrote:

Well, no, they don't state any such thing. Physics is my day job, so I suspect I'm right on this one. A ball thrown straight up has no pause at the top. A child on a swing has no pause at the ends of the arc. And many, many players have no pause on their backswings. You can say they do, but technically, and in physics, you would be wrong.


Quote:
Originally Posted by Snorks
Just a second.. Now, I am not in physics, but at some point a ball tossed up in the air must 'stop' moving up, and 'start' moving down. If this is not a pause, what is it called (for the record I have no idea)? Seems to me this millisecond (or even less then a millisecond), has to be a stop or pause. Same thing would apply to the pool stroke in my opinion. ...

Here's what you're missing. Nobody disputes that the ball stops. The distinction is whether the ball stops for a "length of time." Stopping for a millisecond and stopping for a length of time of exactly zero, i.e. no length of time, seems to be a trivial distinction. But this is the important part. It is not a trivial distinction, because to be stopped for any length of time at all
requires there be no net force acting on the ball during that time. This means either God briefly turned gravity off, or something else is exerting an upward force on the ball equal to it's weight.

Forget which--pause or no pause--is a "best practice" for a pool stroke. That could go either way, or it could depend on the person, or it could just not really matter. But for exactly the above reason, the distinction between no pause and short pause is bigger than it seems.



When there is a constant downward force on the ball, it is not stopped for any "length of time," not a millisecond and not a microsecond.

"The ball is not motionless for a millisecond or a microsecond or even a billionth of a billionth of second. The length of time that it is motionless is zero. That is not a pause."

So, Ceplalus states that a ball thrown exactly vertically reaches a point where it is "not moving in either direction." and I suggest that it is irrefutable, therefore, that he believes that ball has "STOPPED" which is undoubtedly a synonym for being motionless.

Yet Bob states that the ball is NOT "motionless" for even a billionth of a billionth of a second.

I am sure you can see why those comments...as written...are fundamentally contradictory.

I hope you can now see why they're not contradictory.

[...]
I have not seen anyone post a link to any authority that holds that the ball, to the contrary is in constant motion.

That's because so far as I know nobody in the history of the universe has claimed that.

And besides, what constitutes an authority on this subject?

 

[Patrick Johnson]

Ceplalus states that a ball thrown exactly vertically reaches a point where it is "not moving in either direction." and I suggest that it is irrefutable, therefore, that he believes that ball has "STOPPED" which is undoubtedly a synonym for being motionless.

Yet Bob states that the ball is NOT "motionless" for even a billionth of a billionth of a second.

I am sure you can see why those comments...as written...are fundamentally contradictory.

I believe you're right that the comments are contradictory, but it's not because Bob's wrong - it's because that part of Cephalus's description is wrong. There is no time when the ball is moving in neither direction; it's either moving up or it's moving down, with no "in between". There's no time where it's not moving at all.

I think the problem here is the phrase "point in time". That's a purely theoretical concept with no practical reality - you could say that at any point in time when a car is accelerating it's actually not moving, and you'd be right, because movement (and stillness, for that matter) has no meaning with respect to a point in time. Movement and stillness only have meaning over spans of time.

pj
chgo

 

[mikepage]

Ceplalus states that a ball thrown exactly vertically reaches a point where it is "not moving in either direction." and I suggest that it is irrefutable, therefore, that he believes that ball has "STOPPED" which is undoubtedly a synonym for being motionless.

Yet Bob states that the ball is NOT "motionless" for even a billionth of a billionth of a second.

I am sure you can see why those comments...as written...are fundamentally contradictory.

I believe you're right that the comments are contradictory, but it's not because Bob's wrong - it's because that part of Cephalus's description is wrong. There is no point in time when the ball is moving in neither direction; it's either moving up or it's moving down, with no "in between". There's no point in time where it's not moving at all.

I think the problem here is the phrase "point in time". That's a purely theoretical concept with no practical reality - you could say that at any point in time when a car is accelerating it's actually not moving, and you'd be right, because movement has no meaning with respect to a point in time.

pj
chgo

This is not right Pat. Cephalus's description is not wrong. The comments are not contradictory.

"Point in time" is very real. An accelerating car *is* moving provided it's velocity is not zero.

The ball is "stopped" at a point in time.

The problem comes, as you suggest, when "point in time" is confused with "duration of time."

A duration of time is t2 - t1. In an equation, this is usually called delta t (the Greek capital delta means "change in."

In calculus, people consider what happens when the duration gets smaller and smaller and in fact approaches zero. A small "delta" is usually referred to as "d." So a short duration that means "as short as you want it to be" is called "dt."

Often people consider the small change in position (dx) that occurs during that short duration (dt). The ratio dx/dt is the speed the object is moving.

This ratio is defined as the limit at the duration approaches zero of (delta x)
divided by (delta t).

dx/dt is zero at one particular time, but not for any duration of time, not even for a dt. The ratio dx/dt is changing in time. So we can consider d(dx/dt)/dt. This is the "rate of change" of the "rate of change" of x, the position.

dx/dt is known as the first derivative of x with respect to t.

d(dx/dt)/dt is known as the second derivative of x with respect to t, aka the acceleration.

A pause requires dx/dt and d(dx/dt)/dt both be zero, which they're not.

 

[FLICKit]

This topic has hit upon some quite intricate physics details...

First of all, let's be absolutely sure that we're talking about the exact same thing.

When it comes to a ball being tossed in the air (going up and then coming back down):
Incorporating the x,y,z coordinate system where
x would be how far the ball goes
y would be how high the ball goes
z would incorporate the final plane (i.e. to depict a pitcher's curve ball)
Thus, for the purpose of discussing a ball being tossed up in the air, we all are solely referring to the y coordinate only. The x and z coordinates are irrelevant.

When it comes to a pool stick motion
x would be parallel to the plane of the pool table
y would be on the vertical axis
z would be any side motion
Thus for the purpose of discussing a pool stroke, we are solely referring to the x coordinate only. The y and z coodinates are irrelevant to the discussion.

In addition, understanding of course the complicated fact, that every typical pool stroke happens along a parabola-like motion that includes not only x, but also y, (and even the z coordinate - since it's virtually humanly impossible to eliminate all the z component (in other words swerve) in a stroke). But, for the purpose of discussing the pause at the back of a stroke, we are all talking about it with respect to the x coordinate only.


A different analogy for tossing a ball up in the air:
If we took that ball, and placed it on a table, where it sat still. Then the ball would not be going up, nor would it be going down. This is due to the equal and opposing forces of gravity pushing down on the ball, and the table holding the ball up.

Slight Aside: Let's say that the ball was a golf ball (thus having dimples). It would be possible to move the table straight upwards at a rate less than approximately 10 ft/s/s (9.8 is a closer approximation). Whereby the golf ball would remain on the table in that exact same dimple never moving with respect to the table. This could also be done by moving straight down at a rate less than 10 ft/s/s (adjusting for other factors).

Back to analogy: But if you pushed upwards greater than 10ft/s/s then this would impart an upwards force, which causes the ball to propel itself into the air against the fighting force of gravity on the y coordinate. At some point in time the ball would reach equilibrium where it is not going up, nor going down with respect to the y coordinate. It would be exactly as if at the highest point of the ball's flight, there was a table underneath it for an instant and then removed.

Also of note, is that the rate of movement of the ball with respect to the y coordinate would be greatest at the moment after the initial point of flight and the moment before its final point of flight (in other words at the points where the ball was nearest the ground). And its rate of flight would be smallest at the moment before and the moment after it reached its equilibrium (at its highest point).

For example if it started at a rate of 16, then it would go something like
16 8 4 2 1 equilibrium 1 2 4 8 16

In other words the change in distance and speed would be greatest when the ball is nearest the ground, and the change in distance and speed would be very very small when the ball is nearest the top.

 

[mikepage]

This topic has hit upon some quite intricate physics details...

First of all, let's be absolutely sure that we're talking about the exact same thing.

When it comes to a ball being tossed in the air (going up and then coming back down):
Incorporating the x,y,z coordinate system where
x would be how far the ball goes
y would be how high the ball goes
z would incorporate the final plane (i.e. to depict a pitcher's curve ball)
Thus, for the purpose of discussing a ball being tossed up in the air, we all are solely referring to the y coordinate only. The x and z coordinates are irrelevant.

When it comes to a pool stick motion
x would be parallel to the plane of the pool table
y would be on the vertical axis
z would be any side motion
Thus for the purpose of discussing a pool stroke, we are solely referring to the x coordinate only. The y and z coodinates are irrelevant to the discussion.

In addition, understanding of course the complicated fact, that every typical pool stroke happens along a parabola-like motion that includes not only x, but also y, (and even the z coordinate - since it's virtually humanly impossible to eliminate all the z component (in other words swerve) in a stroke). But, for the purpose of discussing the pause at the back of a stroke, we are all talking about it with respect to the x coordinate only.

I agree we can treat it as 1-dimensional motion. But I would not use x. The reason is gravity, which only acts in y, contributes to the restoring force. So a better way to do it is to talk about motion in the x-y plane. Let's say we're talking about motion of the grip hand. The grip hand is attached to the fixed elbow, and the coordinate for the one-dimensional motion is theta, the angle from vertical.

A different analogy for tossing a ball up in the air:
If we took that ball, and placed it on a table, where it sat still. Then the ball would not be going up, nor would it be going down. This is due to the equal and opposing forces of gravity pushing down on the ball, and the table holding the ball up.

OK

Slight Aside: Let's say that the ball was a golf ball (thus having dimples). It would be possible to move the table straight upwards at a rate less than approximately 10 ft/s/s (9.8 is a closer approximation). Whereby the golf ball would remain on the table in that exact same dimple never moving with respect to the table. This could also be done by moving straight down at a rate less than 10 ft/s/s (adjusting for other factors).

Sounds like by "move" you mean accelerate. And the downward limit is 32 ft/s/s rather than 10 (you're thinking meters?) and there is no upward limit. But OK.

Back to analogy: But if you pushed upwards greater than 10ft/s/s then this would impart an upwards force, which causes the ball to propel itself into the air against the fighting force of gravity on the y coordinate.

But it's still on the table, right?, like a golf ball on the floor of a launching rocket? But OK let's assume the table gets out of the picture.

At some point in time the ball would reach equilibrium where it is not going up, nor going down with respect to the y coordinate. It would be exactly as if at the highest point of the ball's flight, there was a table underneath it for an instant and then removed.

This is a big big mistake vis-a-vis the discussion we've been having. When the ball reaches zero velocity, it's turning point, it is definitely not in equilibrium. The point is not at all analogous to the ball being on a table with it's upward and downward forces balanced. This ball, the one in the air, has unbalanced forces.

Also of note, is that the rate of movement of the ball with respect to the y coordinate

(also known as it's speed)

would be greatest at the moment after the initial point of flight and the moment before its final point of flight (in other words at the points where the ball was nearest the ground). And its rate of flight would be smallest at the moment before and the moment after it reached its equilibrium (at its highest point).

OK, but you better purge that word equilibrium from this situation.

For example if it started at a rate of 16, then it would go something like
16 8 4 2 1 equilibrium 1 2 4 8 16

Ouch, it almost hurts to read that word, but if you replace equilibrium with zero speed, then OK.

In other words the change in distance and speed would be greatest when the ball is nearest the ground, and the change in distance and speed would be very very small when the ball is nearest the top.

Yes for the rate of change of distance.
No for the rate of change of speed.

The rate of change of speed is the same everywhere.

At any point in this trajectory, including the top, the ball is accelerating downward at 10 (m/s)/s.

 

[pooltchr]

Does any of this really have anything to do with the game of pool? In over 40 years of playing the game, I have never had a shot that required me to throw the cue ball straight up in the air and try to decide if it stopped at the top or not. I have, however, had thousands of shots that required me to move my cue stick forward in a straight line. The pause between backward and forward motion helps make that happen with a smooth transition. It seems like we may have a little "overanalysis" going on that really doesn't make much difference when it comes to being better players.
JMHO
Steve