Pokermonster 28 Apr 10 01:56 

The point I am trying to get across is this:

If you wish the cueball to follow through after hitting the object ball - yes, of course, you must strike above-centre on the white, but any higher than a fraction above is foolhardy for it will not make one iota of difference to how far the cueball travels. This is governed entirely by how hard you strike, not how high.

I'll disagree here too.  As you've stated already somewhere, there's efficient (linear) momentum transfer when two equal mass objects strike.  However, the angular momentum can only be affected by a torque.  The ball-ball friction is very low and the collision will stop the cue ball linearly while it is still "overspinning".  It then grips the baize and off it goes again.

The ratio of angular to linear momentum is what is altered by the position you strike the cueball and this is important.

* actioned, not action.

Goring.

How would you explain the practical experiment I explained.  The one with the blue ball on the table.

A few forumites tried this and can confirm it works.

Nobody in my presence has ever been able to beat this simple practical test.

And before anyone casts doubt over the quality of cuists involved, several ex world snooker champions are amongst those who have tried.

Anyway, off out now, sir.

Thanks for your interest.  I'll check back later to see if you want to discuss anything further.

pm still baiting with this

even saddo was here when this started, wonder what happened to him

Backspin is possible. Topspin is not

This bothers me too.  Backspin produced by a single impulse at the lower part of the ball which imparts more 'negative' angular momentum than forward linear momentum.  This requires that it be possible to overcome the resistance to motion of the ball with baize.  That being the case, there's no reason it wouldn't happen if hit at the top - the extra torque/force produces more spin than speed will overcome the same resistance to motion.  You can't hold both positions simultaneously.

Hi Treb, hope you are well, sir.

It won't surprise you to learn I believe Mr Daking has had a total mare there with regards his understanding of the physics involved.  He is totally wrong in my opinion: the cueball is following the red into the pocket purely because of its forward momentum from the initial hit and its natural roll.

Presuming he is using a standard pub table cueball (hard to tell from the angle) it will be an eighth of an inch smaler than the red and a full ounce lighter.  This means it will bounce back slightly, picking up BACKSPIN because of its initial forward momentum, and hence following on into the centre pocket.

Hi Goring, hope you are also well, sir.

You are right about the coefficients of friction governing my beliefs.  I have explained this at least twice on the thread though, sir, so it is not fair to say I have not.   I said that the action of the cuetip high on the white was not sufficient to overcome the CoF of phenolic resin on a woolen cloth.

And as to why it is IS sufficient to create backspin and not overspin?  I did explain this, too, many times on this thread.  It is because most of the cueball's mass is above the cuetip whilst imparting backspin. 

As I am sure you know, we are dealing with three types of friction in this scenario: static, sliding and rolling friction.  Imagine a brick on a carpet if you will.  In order to push the brick along the carpet you would first have to overcome the STATIC friction, the coefficients of which are far greater than those needed to keep it moving.  Most people sort of know this in their heads anyway but would be hard pressed to explain exactly why.

It is far easier to start a cueball backspinning instead of topspinning because the static coefficients are far lower with most of the cueball's mass above the cuetip.  With most of its mass below the cuetip I contend it is impossible to spin it under normal conditions, as stated in my opening post.  Roll it, yes.  Topspin it, no.

Once the white is moving after the initial strike, it must now contend with the SLIDING and ROLLING coefficients of friction. In linear motion spheres obviously have a tendency to either slide or roll, or do both.  It can slide forwards and spin backwards quite easily until its tendency to roll takes over (the ROLLING friction coming into force).  The coefficients dictate that the rolling friction will always overcome the sliding friction at some point but, and here's the crucial point, it does not happen the other way around.

Good talking to you all as always, gentlemen.  Thank you for your company.

What's happening when Jimmy White plays his "banana shot"? There is a red over the pocket at the black end of the table. The black itself is tight on the top cushion several inches away from the red over the pocket. In order to get on the black Jimmy pots the red with loads of "topspin" - after hitting the red the cue ball of course hits the top cushion but instead of going all the way back to the baulk end it starts going that way but swerves back on itself ideally ending up in a position near to the top cushion to pot the black.

Is this momentum that causes this or "topspin"?

the test may be true but how often do players play the object ball dead weight when playing with top?

And as to why it is IS sufficient to create backspin and not overspin?  I did explain this, too, many times on this thread.  It is because most of the cueball's mass is above the cuetip whilst imparting backspin.


You need to go further here:  Are you saying that there is a lifting action when struck horizontally below the centre which reduces the reaction force with the baize and allows rotation and that this doesn't exists when hit horizontally at the top?  If so, you still need to explain why the resistance to motion (or static friction) will stop the extra forward rotation.

With most of its mass below the cuetip I contend it is impossible to spin it under normal conditions, as stated in my opening post.  Roll it, yes.  Topspin it, no.


Why?

You objected to the video I posted by stating that it had been done with a hand not a cuetip, but your reasoning here (although incomplete in my view) doesn't rely on that.  I could push the ball down and forward with my hand and it spins extra forward, so your coefficients (unstated sources) don't do the prevention job you're claiming.

Hi Goring.  Thank you for your thoughts again, sir.

In the opening post of this thread I did make sure to use the words "with a cue" and I have repeatedly written phrases to the effect of "under normal playing conditions" or "actioned with a cuetip" or something similar to make it clear I am not including instances where the balls have been doctored or spun by hand.

MIT once created a machine that could spin a cueball at 2000rpm or thereabouts (I can't remember the exact figure but it was something equally impressive).  Once let loose on the table it performed some weird and wonderful effects to everyone's delight. Students at the Sorbonne in Paris managed to install a miniature engine inside a pool ball with, as you can imagine, some rather startling results to the unwary.

I am arguing the case against topspin occuring when actioned with a cuetip under normal playing conditions and the folly of cueing higher up the white in an attempt to impart some sort of overspin above and beyond its natural forward roll.

Reagrds the clip you linked of the banana stroke, please see the answer I gave to AT just above your post.  It's backspin, not topspin causing the swerve.

Could I please have your thoughts on the practical test I laid out, Goring?  And your theories as to why so many people who have tried it now agree that topspin does not work anything like they imagined.

I invite you to try the test, sir.  Or, if you're not a player yourself, ask the best one you know.

Pokey, if it were backspin, it couldn't go to visit the cushion a second time, it would keep going back up the table.

As for your test, I can't verify it at this house.  I will try next weekend as I have a table at the pile.
One possible flaw in your conclusion is that (both) hits aren't strong enough to produce overspin.  This could be amended by allowing the blue to do a few sorties up and down the table but keeping the final position the same for both shots - any objection to that?

Hi Goring.

The final resting place of the blue ball is arbitrary; feel free to change it to suit your needs, sir.  As long as you base your experiment by comparing those shots where the blue stopped in the same place (ensuring equally weighted strikes) the results will be fair and accurate.

I look forward to your findings.  I will be away for a week from tomorrow and may struggle to get online, so please do not think I'm ignoring you should I fail to reply for a while.

Thanks again for your continued interest.

Damned by faint praise!

But thanks anyway, sir.  Hope you get a spare half an hour sometime to have a read through.

What I don't get with the banana shot is why it spins back to the cushion if there is no "topspin". Why does it not do this when the cue ball is just struck into cushion normally - after all if there is no "topspin" both balls are just rolling aren't they?

Nope, not sure that makes sense.  Pokey step in?  (I think he might have answered it already somewhere - he he).

Unless it's 400m freefall I guess.

I'm trying to find a reason for something I'm not convinced of:

In the banana:  The collision with the ball removes the forward speed leaving the spin (which is now overspin which re-grips).  The same happens after colliding with the cushion:  the overspin isn't totally lost yet so after the cushion removes forward speed again (and reverses it) the overspin again regrips.

Not convinced, but that would have to be the answer if it were true.