Thank you Gentleman.
Very useful information.
Randy Goettlicher
Very useful information.
Randy Goettlicher
Niiiiice. ..It's sitting still at that time.
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You are ignoring the energy absorption of the tip and incorrectly applying momentum laws.
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It's really not that important since this whole discussion is what it is, but because a force (your arm) is applied during collision it is no longer an isolated system where momentum is the same before and after the collision. Unless you let go of the cue just before impact, it is not an isolated system that the law can be applied to.Yes, my response assumes an elastic collision.
But what do you mean by incorrectly applying momentum laws?
It's really not that important since this whole discussion is what it is, but because a force (your arm) is applied during collision it is no longer an isolated system where momentum is the same before and after the collision. Unless you let go of the cue just before impact, it is not an isolated system that the law can be applied to.
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It's really not that important since this whole discussion is what it is, but because a force (your arm) is applied during collision it is no longer an isolated system where momentum is the same before and after the collision. Unless you let go of the cue just before impact, it is not an isolated system that the law can be applied to.
I think leaving out the behavior of the tip is pretty significant. Two billiard balls colliding would approximate an elastic collision. Wrap one of them in thick leather and it will be a very different collision.
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And it's not just a theoretical estimate. It was measured as part of the Jacksonville Experiment in 1998. It turns out that the stick does almost instantly go down to 50% of its initial speed and then over a period of about 20 milliseconds go back up to about 80% of its initial speed as the hand and wrist finally get more force into the stick after contact.From the impulse (change in momentum) and the knowledge the contact takes about a millisecond, you can estimate the tip-ball force during the collision. It is very high compared to anything you can apply with your arm and fleshy hand.
And it's not just a theoretical estimate. It was measured as part of the Jacksonville Experiment in 1998. It turns out that the stick does almost instantly go down to 50% of its initial speed and then over a period of about 20 milliseconds go back up to about 80% of its initial speed as the hand and wrist finally get more force into the stick after contact.
The spring constant of the tip-ball collision is quite high which is why contact takes only 1-2 milliseconds.
The spring constant of the grip-hand is much lower and cannot apply much force until it is wound up a little, which takes time and cue travel.
We just had this conversation a little while ago, I believe, and before:
https://forums.azbilliards.com/showthread.php?t=494978
https://forums.azbilliards.com/showthread.php?p=4631030
As for whether any of this is useful, probably not. If the fact that your hand pressure is irrelevant at contact allows some players to give up their death grip on break shots, then maybe it is useful.
Let the cue do the work.
Randy,Hey PJ
What is the correct formula to use to calculate:
energy transfer from cue tip to cue ball? In other words, how fast is the cue ball traveling at the time of impact?
I have been lead to understand that with a dead center hit, the cue ball leaves with about an additional 10% of speed.
If people want to see this in action, see:It turns out that the stick does almost instantly go down to 50% of its initial speed and then over a period of about 20 milliseconds go back up to about 80% of its initial speed as the hand and wrist finally get more force into the stick after contact.
Welllllll, at the time of impact the cueball is moving, as Earth does rotate. You can take this to insane depths, but a general base is all that is needed here.
And it's not just a theoretical estimate. It was measured as part of the Jacksonville Experiment in 1998. It turns out that the stick does almost instantly go down to 50% of its initial speed and then over a period of about 20 milliseconds go back up to about 80% of its initial speed as the hand and wrist finally get more force into the stick after contact.
If people want to see this in action, see:
HSV B.40 – Stroke speed and acceleration analysis, with Bob Jewett
Enjoy,
Dave
The Jacksonville Experiment video did show the grip hand at impact for some shots. Quite remarkable were the ripples in the skin of the hand, IIRC. The video was distributed starting in 1999 or so and for a while the whole thing was on AZB.Do you know if they published a high-speed video of the hand holding the cue at the moment of impact? I suspect one would see a lot more movement than one would expect, even with a death grip. I'm thinking of those slow motion videos of people's faces jiggling like jello after getting hit with something.
If people want to see this in action, see:
HSV B.40 – Stroke speed and acceleration analysis, with Bob Jewett
Enjoy,
Dave
Except this assumes an isolated system where the cue (or the cue and your arm) are detached and hurtling toward the cue ball. The fact that you are continuing to apply force through impact is why the cue doesn't slow to that lower predicted speed that ignores the external force. The less your strength allows the cue to slow at impact the more momentum is transferred to the ball. A power hitter in baseball has to be fast and strong.The fact that cue speed drops by about 40% actually is a very good indication that the weight of the arm doesn't contribute meaningfully to the impact. Given a cue that's 3x as heavy as the ball and a coefficient of restitution of 0.75, you'd expect the cue to retain 56% of its speed after impact. If the arm doubled the effective mass of the cue, you'd expect it to retain 75% of its speed.
Except this assumes an isolated system where the cue (or the cue and your arm) are detached and hurtling toward the cue ball. The fact that you are continuing to apply force through impact is why the cue doesn't slow to that lower predicted speed that ignores the external force. The less your strength allows the cue to slow at impact the more momentum is transferred to the ball. A power hitter in baseball has to be fast and strong.
I did and no, not even a little bit.You want to actually read my post and try again?
I think Bob and Dave and Mike are saying the soft skin of the hand effectively isolates the cue from your hand/arm during the millisecond of contact.... this assumes an isolated system where the cue (or the cue and your arm) are detached and hurtling toward the cue ball.
The fact that you are continuing to apply force through impact is why the cue doesn't slow to that lower predicted speed that ignores the external force. The less your strength allows the cue to slow at impact the more momentum is transferred to the ball.