Cue Tip Contact Myth-Busting Truths in Super Slow Motion

pvc lou said:
The cb acquired it's spin from its collision with the tip. So, the spin induced throw is quite relevant.

Simple example:

Have you ever noticed going from playing with a hard tip to a soft tip (or the reverse) that the cut angle changes slightly when you use english? Balls that you expect to make can hang up in the pocket due to this unintentional spin.
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Do you suppose that the cut angle might have changed from squirt??
PS I guess Im late to the party, already asked but if the tip contact time is "twice as long" I would guess that has an effect on squirt.
 
buckshotshoey said:
Yes And no. A hard tip is actually denser than a soft tip so it has more mass. Therefore Theoretically, a hard tip will deflect slightly more than a soft tip. But For all practical purposes it is almost immeasurable
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So immeasurable difference in end mass with different tip hardness. So we agree.
 
pvc lou said:
COR is a measure as defined in the work of Dr. Dave is a measure of the transfer of linear kinetic energy. Rotational kinetic energy is not considered.

Therefore, sigh. What you wrote is not useful to the present analysis.
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So… vector math wasn’t part of your studies? Amazing. Do you argue with Russians on how to speak Russian? I wouldn’t think so. There are some fundamental parts of this discussion that you don’t seem to be familiar with, so nothing said will ever make sense to you. I believe Mr Jewett had already addressed this, I presume with you. You might have responded with, “ouch.”

I’m not here to convince you. I’d only request that you do more study on Physics fundamentals so we can have meaningful conversations. As it is, we’re not there.
 
Patrick Johnson said:
You’ve misread things again. The cue’s “linear kinetic energy” produces both linear ("translational") and rotational acceleration on the ball.

pj
chgo
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Patrick, I'm doing my best not to go all "Bob Jewett" on you by giving you homework and telling you that you're just "winging it."

Yes, the cue's kinetic energy is linear, and when it strikes the cb, this energy will be partly converted into linear and rotational KE. However,
the coefficient of restitution is a ratio of differences in linear velocities. It does not account for rotation of the cb. I'm sorry for linking the wikipedia article for COR, but I got Fred and fastone371 to get to next.
 
Cornerman said:
So… vector math wasn’t part of your studies? Amazing. Do you argue with Russians on how to speak Russian? I wouldn’t think so. There are some fundamental parts of this discussion that you don’t seem to be familiar with, so nothing said will ever make sense to you. I believe Mr Jewett had already addressed this, I presume with you. You might have responded with, “ouch.”

I’m not here to convince you. I’d only request that you do more study on Physics fundamentals so we can have meaningful conversations. As it is, we’re not there.
Click to expand...

Hi Fred,

I have been trying to respond for a third time to your last post to me. I admit that the two previous replies were made in haste, and I apologize for that.

Regarding my studies, I'll tell you all that you want to know in private. I believe that a scientific debate ought not involve a comparison of credentials. I somewhere got the impression that you are an engineer. If that's so, I am disappointed that you would stoop to an appeal to credentials or perceived intelligence rather than disputing the merits of my arguments. But I'm not surprised, Bob Jewett did it, and so did the Doctor. I have, meanwhile, done my best to refrain from responding in kind...perhaps I failed a couple of times though.

Please see post #428 as a first response to the question of COR.

As for the question at hand as I see it. Does tip hardness and/or contact duration have any significant influence when putting spin on the ball when we're playing pool. I think the answer is clearly yes. There are many simple examples to demonstrate that, but I will again cite Mike Page's comment, which, to Dr. Dave's credit, is posted on his hit efficiency page. He makes a very cogent argument regarding the importance of contact time on the collision dynamics, and it is as follows:

from Mike Page (in AZB post):
A softer tip might take almost twice as long to compress and decompress against the ball than a hard tip. And this, by itself, doesn’t affect energy transfer at all. But there is some empirical evidence hard tips tend to be a little more elastic (have less energy loss). Also, this is going to be a tip-to-tip thing. It is not like here is anything automatic about softer tips that make them less elastic.
For the cueball to “feel” the entire weight of the cue, the tip-ball collision has to last long enough for the signal the collision is in progress to travel back and forth across the stick a sufficient number of times. So at some point as we get harder and harder tips, the cueball might not feel the full weight of the cue.
This is a little like a fast-moving train hitting a car that is on the tracks. The car will be launched with a speed characteristic of being hit by just the engine or the engine plus the first couple of cars. The collision time would have to be longer for the car to feel the weight of the rest of the train cars as they crush across the couplings.
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Here's an idea: combine the Aiming Forum and Cue-tip Hardness Effects into one fun filled lunatic fringe forum. Boy-howdy as Buddy Hall likes to say. Throw facts/science/data OUT the window and just have a free-fire-zone of competing myths, tales, legends and all around buffoonery. Don't let facts get in the way of a loony-toons 'guess fest'. ;)
 
garczar said:
Here's an idea: combine the Aiming Forum and Cue-tip Hardness Effects into one fun filled lunatic fringe forum. Boy-howdy as Buddy Hall likes to say. Throw facts/science/data OUT the window and just have a free-fire-zone of competing myths, tales, legends and all around buffoonery. Don't let facts get in the way of a loony-toons 'guess fest'. ;)
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Why are you always looking to send people to the fringe, garczar?

Why does it make you so mad that someone doesn't agree with you?
 
pvc lou said:
...the coefficient of restitution is a ratio of differences in linear velocities. It does not account for rotation of the cb.
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It contributes to the linear force being applied to the CB, which accounts for rotation (and linear speed) of the CB.

Visualizing these subtle forces and effects can be tricky - it's not surprising that you (and others) misunderstand it.

pj
chgo
 
pvc lou said:
Hi Fred,

I have been trying to respond for a third time to your last post to me. I admit that the two previous replies were made in haste, and I apologize for that.

Regarding my studies, I'll tell you all that you want to know in private. I believe that a scientific debate ought not involve a comparison of credentials. I somewhere got the impression that you are an engineer. If that's so, I am disappointed that you would stoop to an appeal to credentials or perceived intelligence rather than disputing the merits of my arguments. But I'm not surprised, Bob Jewett did it, and so did the Doctor. I have, meanwhile, done my best to refrain from responding in kind...perhaps I failed a couple of times though.

Please see post #428 as a first response to the question of COR.

As for the question at hand as I see it. Does tip hardness and/or contact duration have any significant influence when putting spin on the ball when we're playing pool. I think the answer is clearly yes. There are many simple examples to demonstrate that, but I will again cite Mike Page's comment, which, to Dr. Dave's credit, is posted on his hit efficiency page. He makes a very cogent argument regarding the importance of contact time on the collision dynamics, and it is as follows:

from Mike Page (in AZB post):
Click to expand...
Whether you have credentials or not is irrelevant. When you are misunderstanding basic physics terms, meaningful conversations basing things on those physics terminology is pointless.

Your argument also keeps changing, so it’s difficult which head to cut off. Mike’s post is about tip efficiency and the speed of sound. Using real world measurements on tip contact time should point to an answer of how much of a cue’s mass is felt by a hard tip at X speed.

None of his post is discussing spin/speed ratio .
 
pvc lou said:
COR is a measure as defined in the work of Dr. Dave is a measure of the transfer of linear kinetic energy. Rotational kinetic energy is not considered.
Click to expand...

The spin (rotation) is directly related to the speed (translation) based solely on the tip offset (lever or moment arm) from the center of the ball. Math, physics, common sense, and experience at the table all agree on this point. If you want to see the math and physics, it is here:

 
I just remembered that I did a fairly careful experiment many years ago trying to determine whether or not a shaft being LD or not, or a stroke using a swoop/swipe motion or not, affects the amount of spin that can be imparted to the CB. I wasn't specifically testing for tip hardness differences, but I did use two tips of different hardnesses. Here it is:


The video at least demonstrates a simple yet effective way to perform such an experiment in a way that anybody can easily do on their own. I might do a more careful video soon that looks specifically at a wider range of tip hardnesses. I don't expect the results to be any different, but it will still be fun to attempt to create a video that might convince even to the "Soft Tip Mythers."

Here's another set of experiments I also did many years ago attempting to measure CB deflection differences over a wide range of tip hardnesses on the same cue:


This doesn't directly address the soft-tip-maximum-spin myth being discussed here, but it is still related and might give people other ideas for how to do tests on their own.

Enjoy!
 
dr_dave said:
The spin (rotation) is directly related to the speed (translation) based solely on the tip offset (lever or moment arm) from the center of the ball. Math, physics, common sense, and experience at the table all agree on this point. If you want to see the math and physics, it is here:

Click to expand...
Tell me if I'm describing this correctly....

Let's say you strike a cue ball with a 100% exact aim point with both tips. The hard tip won't compress as much as a soft so the actual contact point is relatively small and concentrated.

Say the soft tip aim point is EXACTLY the same, but as the tip contacts and compresses, it is actually is producing rotation at a point closer to the center of the ball?

If I am seeing this right, this could be why a hard tip produces more rotation then a soft. The longer "lever" (or moment arm) produces more torque (as minimal as that might be).
 
Cornerman said:
Whether you have credentials or not is irrelevant. When you are misunderstanding basic physics terms, meaningful conversations basing things on those physics terminology is pointless.

Your argument also keeps changing, so it’s difficult which head to cut off. Mike’s post is about tip efficiency and the speed of sound. Using real world measurements on tip contact time should point to an answer of how much of a cue’s mass is felt by a hard tip at X speed.

None of his post is discussing spin/speed ratio .
Click to expand...

How has my argument changed?

Excuse me Fred, but your use of the terminology of mechanics is incoherent.

Are you really an engineer?


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