Physics Quiz - Poll

[jsp]

Case 1: You stroke a cue ball with complete center ball such that it departs straight down the table with absolutely no spin (no side spin nor top/bottom spin).

Case 2: You stroke a cue ball such that you impart the same impulse of force on the CB as the previous case, but this time you hit the CB with one tip of left english (without miscuing). The CB will veer off slightly to the right due to squirt, and will also have some side spin (bot no top/bottom spin).

Ignoring the effects of cloth friction, which cue ball will have the greater total kinetic energy (both translational and rotational) after leaving the cue?

(Jal...I'd leave you out of this quiz. )

 

[BigCat]

Your question is a bit ambiguous. You are asking which case has the most energy. The Law of Conservation of Energy states that energy cannot be created or destroyed, it can only change form.

So to query as to which case has more energy, while ignoring friction, is more simply a question of which case do you strike the cb with more kintetic energy (as potential energy will be the same for either case assuming you are using the same cb, cue, person, etc...). If you strike the cb in each case with the exact same amount of kinetic energy, the total kinetic energy for each case is the same, regardless if you are taking into account friction (friction will just tranlsate to another form of energy).

Are you trying to find out which case has more energy after the affect of the english takes? Or are you just referring to the total energy of the cb from point of contact to when the cb stops rolling? If it is the latter, you've already answered your own question. It is the same. But if you are referring to translational and rotational only, then you can't ignore friction as the aforementioned law states that energy will be lost due to some of the friction and be converted into heat. This will also cause a different outcome for the cb's path because the more friction, the more kinetic energy will be lost and therefore cause the cb to lose more of its initial kinetic energy (and therefore cause less translational movement). Rotational movement is more relative to when the cueball stops skidding from the applied force/english, and again is directly related to friction.

 

[Irish634]

Ow! My head hurts!

 

[td873]

Case 1: You stroke a cue ball with complete center ball such that it departs straight down the table with absolutely no spin (no side spin nor top/bottom spin).

Case 2: You stroke a cue ball such that you impart the same impulse of force on the CB as the previous case, but this time you hit the CB with one tip of left english (without miscuing). The CB will veer off slightly to the right due to squirt, and will also have some side spin (bot no top/bottom spin).

Ignoring the effects of cloth friction, which cue ball will have the greater total kinetic energy (both translational and rotational) after leaving the cue?

(Jal...I'd leave you out of this quiz. )

Also ignoring inconsistencies in the tip, ferrule, and shaft. Oh, and assuming the same weather, the same translation of energy into sound, and no foreign objects at the contact point(s).

I think if you put enough qualifiers on there, you can get the answer to be whatever you want

-td

 

[ShootingArts]

Three things can happen to energy in a collision

Deleted reply. Later posts by the OP make it plain this thread is yet another time waster.

I'll start the poll on how two things can be exactly the same but different.

Hu

 

[Johnnyt]

Just shoot the ball into the pocket...geeeeeeeeez. Johnnyt

 

[ShootingArts]

well . . . .

Just shoot the ball into the pocket...geeeeeeeeez. Johnnyt

Would that be with CIT, SIT, or my favorite, BFL?

Hu

 

[Hierovision]

I think slightly more kinetic would be transferred in case 1 due to the cue being structurally designed to perform that way. Not much more but very slightly more.

 

[3andstop]

Just shoot the ball into the pocket...geeeeeeeeez. Johnnyt

This by far is the best answer in terms of advancing your pool game.

 

[jsp]

So to query as to which case has more energy, while ignoring friction, is more simply a question of which case do you strike the cb with more kintetic energy (as potential energy will be the same for either case assuming you are using the same cb, cue, person, etc...). If you strike the cb in each case with the exact same amount of kinetic energy, the total kinetic energy for each case is the same, regardless if you are taking into account friction (friction will just tranlsate to another form of energy).

I don't disagree with what you just said here. But read what I highlighted in bold. You're stating a different question than what I originally wrote. Reread the original question, and look at what I specifically italicized.

Are you trying to find out which case has more energy after the affect of the english takes?.

I'm trying to find out exactly what I wrote...Which cue ball has more total kinetic energy right after impact with the cue? Forget completely about the table...let's say you did this in zero-gravity space.


This question is more of an idealized physics problem rather than a practical pool problem. It's one of those questions that you would more likely get correct if you don't have any background in physics...LOL.

It deals with a problem that I have been struggling with for a long time. It comes up whenever I read physics papers regarding squirt. To me, the answer isn't very intuitive. Again, the key to the question is to carefully read what I italicized in the original post.

 

[jsp]

Just shoot the ball into the pocket...geeeeeeeeez. Johnnyt

What?? You mean you don't mentally compute the amount of kinetic energy of the cue ball every time you stroke a shot?

Maybe that's why I'm still a D player.

 

[TATE]

Case 1: You stroke a cue ball with complete center ball such that it departs straight down the table with absolutely no spin (no side spin nor top/bottom spin).

Case 2: You stroke a cue ball such that you impart the same impulse of force on the CB as the previous case, but this time you hit the CB with one tip of left english (without miscuing). The CB will veer off slightly to the right due to squirt, and will also have some side spin (bot no top/bottom spin).

Ignoring the effects of cloth friction, which cue ball will have the greater total kinetic energy (both translational and rotational) after leaving the cue?

(Jal...I'd leave you out of this quiz. )

I have no physics experience at all, but if the cue is in the same position in both shots, then the tip is moved off center, logic tells me you are delivering a glancing blow. The energy vortex created is channeled into a "V" shape. Part of it is used to propel the ball forward, part of it sideways, part of it is lost due to less tip friction, and part of it is used to spin the ball.

A center ball hit will always produce the most forward speed (energy) using identical strokes. That's why we break with center ball.

Chris

 

[TATE]

A more difficult and relevant question would be:

Allowing for friction, would a cueball struck at exact center impart more energy on impact than a cueball struck one tip above center?

Chris

 

[CamposCues]

Center Ball

I believe center ball also. If english is applied you will see the cue ball still spinning after the break meaning some energy is still left with the cue ball. If you hit center ball all the energy is transferred to the rack.

 

[bagofpaper]

Your question is a bit ambiguous. You are asking which case has the most energy. The Law of Conservation of Energy states that energy cannot be created or destroyed, it can only change form.

That statement of the conservation of energy doesn't give any insight into this question in because kinetic energy is simply being given to the cue ball by transferring momentum from the cue to the cue ball. It isn't being "created" or even "changing forms" (unless you want to talk about where it came from i.e. chemical energy in your muscles) just transferred from the cue stick to the cue ball.

The second case has more kinetic energy right after contact because you hit the cue ball with the same amount of impulse which simply means you transferred the same amount of linear momentum. By giving the same amount of momentum to identical cue balls you've made them travel at the same speed. Since they are traveling at the same speed they have the same linear kinetic energy. The difference is that in the second case you also spin the ball with english giving some rotational kinetic energy as well. Since the total kinetic energy is just the sum of the translational and rotational kinetic energies, case 2 gives the cue ball more kinetic energy.

 

[Jal]

Jsp,

You have a lot of courage. Even though 99% of the things talked about on this forum will never conceivably help one's game, there's something about physics that brings out the inevitable "just shove the balls in the pockets and don't worry about this stuff" responses. If you're going to bring up this ignominious subject, you'd better have a practical application!

I know I'm banned from offering an answer, but let me say that I don't think many will understand "impulse of force", in the specific sense in which you mean it. Few know what an impulse is, or, I suppose, what a force is.

Jim

 

[jsp]

Jsp,

You have a lot of courage. Even though 99% of the things talked about on this forum will never conceivably help one's game, there's something about physics that brings out the inevitable "just shove the balls in the pockets and don't worry about this stuff" responses. If you're going to bring up this ignominious subject, you'd better have a practical application!

Lol. Um...yeah, I do have a practical application for this thread. Don't think about kinetic energy when stroking the CB or you'll become a D player like me.

I've posted these zany, impractical, physics/math-type threads before. Why stop now? Besides, I was bored here at work.

I know I'm banned from offering an answer, but let me say that I don't think many will understand "impulse of force", in the specific sense in which you mean it. Few know what an impulse is, or, I suppose, what a force is.

You mean "impulse of force" isn't as common knowledge as chalking your tip? Hehe.

Hey, you voted! I guess everyone knows now what the correct answer is.

 

[jsp]

That statement of the conservation of energy doesn't give any insight into this question in because kinetic energy is simply being given to the cue ball by transferring momentum from the cue to the cue ball. It isn't being "created" or even "changing forms" (unless you want to talk about where it came from i.e. chemical energy in your muscles) just transferred from the cue stick to the cue ball.

The second case has more kinetic energy right after contact because you hit the cue ball with the same amount of impulse which simply means you transferred the same amount of linear momentum. By giving the same amount of momentum to identical cue balls you've made them travel at the same speed. Since they are traveling at the same speed they have the same linear kinetic energy. The difference is that in the second case you also spin the ball with english giving some rotational kinetic energy as well. Since the total kinetic energy is just the sum of the translational and rotational kinetic energies, case 2 gives the cue ball more kinetic energy.

Good answer. This is correct.

Although you're applying the same force impulse (magnitude and time duration) to the CB in both cases, you're actually imparting more energy into the CB for the second case. So Case 2 will have the greater kinetic energy.

So the further you strike the CB away from center ball, provided you apply the same force impulse and you don't miscue, the CB will have greater kinetic energy. Kinda wild, huh?

I'll leave it up to you to figure out why you probably won't notice this in the real world.

 

[BigCat]

The difference is that in the second case you also spin the ball with english giving some rotational kinetic energy as well. Since the total kinetic energy is just the sum of the translational and rotational kinetic energies, case 2 gives the cue ball more kinetic energy.

I don't agree. So, if you impart more rotational energy, then you also lessen the amount of translational energy. The translational energy is not conserved as you apply more "rotational" force. Think of this to an extreme: if you applied "20 tips" of english and struck the cue ball with the same force, the cb would not travel very far (translational energy would be small) but would have a very high amount of rotational energy.

 

[BigCat]

So the further you strike the CB away from center ball, provided you apply the same force impulse and you don't miscue, the CB will have greater kinetic energy. Kinda wild, huh?

This is impossible, rotational + tranlational must still equal the original force applied, one can only transfer to the either, not increase rotational and traslational stay the same.