Sidespin on a stopshot

[Deadon]

I'm thinking along these lines also but I believe its more complicated than that because you have angular momentum from the spinning balls to account for as well.

It seems there is no initial angular momentum at the beginning, with the given question taken as a perfect hit. I believe mikepage is correct, and as jsp pointed out, is dependent on the friction/surface of the balls used. How far it moves to the left depends also on the initial velocity of the CB as the reaction is a percentage component of the velocity/speed.

 

[mikepage]

I'm thinking along these lines also but I believe its more complicated than that because you have angular momentum from the spinning balls to account for as well.

I agree that angular momentum must be conserved in the collision. But that's a separate constraint. It doesn't affect the conservation of linear momentum.

mike page
fargo

 

[Cornerman]

Scott, are you assuming completely frictionless balls?

No. I'm sure he's assuming that if he shoots a straight in shot, and the cueball is left spinning madly in place without wavering to the side, then he must have hit the balls such that at the moment of impact, the line of centers is in direct line of the initial cueball aim.

Which of course, it can't be. In order to have the cueball spinning in place madly, without wavering to the side, the cueball must slightly cut the object ball. Newton's Third Law.

Fred

 

[Cornerman]

BUT BUT BUT ....

We have all seen a cueball stop dead with spin *and* an object ball throw to the right! Anyone who plays straight pool knows he can stop a cueball dead and throw an object ball.

Actually Mike, I have never seen this. I've heard other people say it, and have seen it written about in books. But, I've never seen anyone do this.

Fred

 

[mikepage]

Actually Mike, I have never seen this. I've heard other people say it, and have seen it written about in books. But, I've never seen anyone do this.

Fred

Could be the balls have to be dirty...

Try this. I was doing it this morning.

Put an object ball a chalk cube from the long rail near the side pocket. Aim for a straight-in shot down the rail past the side pocket to the corner pocket. Try, using spin, to throw the object ball out of the pocket (away frojm the rail) *without* the cueball touching the cushion. I could throw the object ball out of the pocket stopping the cueball dead provided the cueball started close enough to the object ball.

mike page
fargo

 

[pharaoh68]

While Chris' original response of "How does one hit left english and centerball (or words to that affect) is truly funny, Tennessee Joe hit it right on the head. By putting left english on the cue ball, at the exact moment of impact, the most simple law of physics applies: For every action, there is an equal and opposite reaction". As a result, putting a clockwise spin on the cue ball will cause the cue ball to grip the object ball for a fraction of a second, and force it to spipn in the opposing direction.

As well, that fraction of a second "grip" on the object ball, will generate an ever-so-slight movement to the left for the cueball and an ever-so-slight movement to the right for the object ball.

 

[pete lafond]

May seem like a stupid question, but how does one hit centerball with left english? Doesn't centerbal imply the CB is hit in, well, the center? To me that means no left english and no right english.

It would be OK to just say left or as in another thread stated "9 oclock".

 

[Gregg]

Doesn't spit have friction?

J/K. I have seen this effect on Bryne's Standard Vol. II tape, right Mr. Bob Jewitt?

 

[pete lafond]

I'm aware that if I hit that shot I do not allow for throw. Can it throw? Sure. Does it always throw enough to be measured, or see the effect? I don't think so. In fact I think the shot is just as easy with the sidespin, as opposed to hitting center ball, because any slight offset from center ball can throw the object ball more than the spinning cueball.

On the frozen rail shot do you think you have to aim for more rail when using inside as opposed to center ball?

Do you think like I do that inside english produces generally much less throw than outside or center ball? If so, what is your explanation, and why couldn't this effect contribute to minimizing the throw to near zero on a straight shot?

unknownpro

Curve would have more effect than throw and you hit it with the amount varying to the point you do not count on it.

If we stabilize so curve does not exist on a dead center straight line impact, the CB and OB will not part the from a straight path. In outer space in a fictionless environment, yes. However the weight of the balls on the felt will keep the balls in a straight line. Should be almost no change. Opinion.

 

[enzo]

You're certainly right about how common misconceptions about many strokes and shots are. Just look at the poll...more than half believe that the CB will move sideways...when in fact, it will NOT.

Scott Lee
www.poolknowledge.com

great point, one that i was gonna make, ie, either way you see it there are commom misconceptions obviously.

 

[enzo]

It's actually possible to use left english to pot a straight in shot and make the CB move slightly right after hitting the OB. But on this shot you are actually hitting the OB right of the point along the line through the balls to the pocket. The left spin throws the OB to the right.

But as the question was stated. If the CB and OB contact at the points along the straight line, the CB will move slightly left. It's a proven and well known effect.

Colin

great post.

 

[pete lafond]

We have all seen a cueball stop dead with spin *and* an object ball throw to the right! Anyone who plays straight pool knows he can stop a cueball dead and throw an object ball. What's the deal? Is the physics described above only kinda right? Or only right in an idealized world? Or does it require elastic collisions or some such thing? ..

Yes in straight pool this shot is often used except we play to the part of the pocket that yeilds the straightest shot, draw the CB to stop (Kills it) and curve the CB with a normal stroke.

I've seen many players say they threw the ball when in fact the result was achieved by curve. Watch when someone misses a shot with side english (generally the slower hits), they didn't throw it out of the pocket as they said- the CB curved and they just missed. Opinion.

 

[enzo]

opinion of original poster...

I read this question as: When two balls collide such that the line of centers at the moment of contact is parallel to the direction of the cue ball's travel (full ball hit) and the cue ball has stun side spin, does the cue ball stop dead (and spin) or move ever so slightly to the side (and spin)?

This IS the question I posed. Thanks, nicely stated.

i dont have a lot of time today, but in nine ball, if i can only see like 14/15 of a ball (ie, i cant quite see the whole ball), and i want to stop the cueball for a safety, i use inside english and the cue ball stops dead sure enough, but i did not hit a full ball.

yes, if you see the cueball stop and spin the object ball was cut slightly in the same direction of the spin (rewording this statement to be more understandable is encouraged, lol).

the poll was interesting. it was about even and then moving slightly left took a slight advantage when jewett and co. spilled the beans (at least thats the way i saw it).

anyway, wish i had more time today. thanks for all the nice posts

 

[Jal]

I guess it depends on your definition of "slightly". Friction will cause the ball to move left, as well as the object ball to move right. The degree to which this happens depends on how clean, or dirty, the balls are at the contact point.

I think "slightly" in this case means about 1"-4". If you use a tip offset near maximum, I think you might actually have a problem trying to get it to move less than one inch. This is pretty much independent of how hard you the cueball. It's almost a constant over the range from slow to fast speeds assuming some cloth irregularity doesn't stop it prematurely.

As you reduce the offset throw increases, until at approximately 1/3 of the maximum offset (this varies a bit with speed), you should be able to move the cueball sideways about a third of a diamond with a firm hit.

Jim

 

[Bob Jewett]

Actually Mike, I have never seen this. I've heard other people say it, and have seen it written about in books. But, I've never seen anyone do this.

Fred

How about the demo shot I posted some time ago in which the cue ball and object ball both go to the same side of their line of centers? (to the left of the line with right english) It's a small adjustment to get the cue ball to stop dead and have the object ball move to the side. Here's a diagram.

http://www.sfbilliards.com/throwtest.gif

The maximum separation is smaller than many proponents of spinning the ball in seem to think, but the effect is real.

 

[zeeder]

I think "slightly" in this case means about 1"-4". If you use a tip offset near maximum, I think you might actually have a problem trying to get it to move less than one inch. This is pretty much independent of how hard you the cueball. It's almost a constant over the range from slow to fast speeds assuming some cloth irregularity doesn't stop it prematurely.

As you reduce the offset throw increases, until at approximately 1/3 of the maximum offset (this varies a bit with speed), you should be able to move the cueball sideways about a third of a diamond with a firm hit.

Jim

If the cueball is going straight, i.e. not curving, at the moment of impact then I can't imagine an instance where the ball will move more than an inch. You figure that if the cueball moves an inch then the object ball is going to move by 5 or 6 inches with in a 4-5 foot shot!

 

[pete lafond]

This IS the question I posed. Thanks, nicely stated.

i dont have a lot of time today, but in nine ball, if i can only see like 14/15 of a ball (ie, i cant quite see the whole ball), and i want to stop the cueball for a safety, i use inside english and the cue ball stops dead sure enough, but i did not hit a full ball.

I'm not sure if anyone else noticed this but if it seems that you can only see 14/15ths of the ball you can shoot it anyway. Seems like an illusion. It has always worked for me.

 

[Jal]

I'm thinking along these lines also but I believe its more complicated than that because you have angular momentum from the spinning balls to account for as well.

As you say, it is more complicated.

The cueball doesn't move straight sideways because of the inelasticity of the collision, which gives it a forward component of velocity (if the weights of the balls are about equal). So the cueball starts off neither straight ahead nor straight to the side.

The cueball's spin then causes it to follow a curved (spiral) path until it reaches natural roll. This is because it has to "climb over the cloth", ie, it's the same mechanism which causes it to slow down when rolling. So even if the cueball's spin axis is perpendicular to the slate, it's effectively inclined with respect to the cloth. Normally this curvature is unoticeable, the effect is so small. But here we have a very high spin/speed ratio.

Jim

 

[Tennesseejoe]

How about the demo shot I posted some time ago in which the cue ball and object ball both go to the same side of their line of centers? (to the left of the line with right english) It's a small adjustment to get the cue ball to stop dead and have the object ball move to the side. Here's a diagram.

http://www.sfbilliards.com/throwtest.gif

The maximum separation is smaller than many proponents of spinning the ball in seem to think, but the effect is real.

In this example does the cue stick line up parallel to the rail or does the tip point slightly to the left?

 

[Bob Jewett]

In this example does the cue stick line up parallel to the rail or does the tip point slightly to the left?

I think that depends on how much squirt your stick has. A typical house stick might be parallel.