CB transfers no spin to OB - Steve Davis

mikepage said:
I can think of two other causes (besides transferred spin) of the middle ball going forward. First is, as I said, topspin on the middle ball from friction with the cloth. Second is any inelasticity of collision between the two object balls would cause the middle ball to go forward.

I'm sceptical. I would think if it works to any practical degree for the backspin shot (to put follow on the middle ball), it should also work with the topspin shot (to put backspin on the middle ball). I haven't seen anthing that convinces me.

mike page
fargo
I am talking about high speed shots with the 2 OBs close or touching (within a couple of inches, so cloth friction is insignificant).

I am also contrasting stun to draw shots. With stun, the inelasticity of the collision allows the middle object ball to travel forward some. The draw can add significantly to this forwad motion by adding a component of topspin to the middle CB.

For a topspin shot to make the middle ball come backward of the tangent line, it would have to be greater that the forward component produced by the inelasticity of the OB to OB collision. It is likely of similar or slightly less magnitude though, so you won't see backward movement.

You can however easily test the draw converted to topspin effect by hitting a few straight shots on two touching balls. Hit some with stun and others with draw. See how far the middle ball travels forward with the two methods.
 
I think that the shot where you need to make two object balls in the same pocket is well-known. I have made it many times. You need to hit the cb below centre. It doesn't require that much accuracy if the first ball is hanging.

It's mainly an 8-ball shot, sometimes the easier way to make the 8 is to pocket it together with another hanging ball. In 9-ball I think it wouldn't come up very often, only for safety play.
 
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Jal said:
Given the same surface conditions and initial cueball speed and cut angle, both types of balls should throw the same, but the smaller snooker balls should acquire more spin.

Jim
Jal is correct about this. Both balls would have the same amount of throw, given the same coefficient of friction, CB velocity, and cut angle. However, we'd also have to assume the same coeffecient of restitution (measurement of elasticity) between the pool and snooker balls. The masses of the balls can be cancelled from both sides of the equation, and the diameter of the balls don't figure into the equation (at least to first order, since the diameter can have second order effects to the friction and elasiticity properities). According to Dr. Dave's math, the amount of throw is equal to arctan (mu/e), where mu is the coefficient of friction and e is the coefficient of restitution. This equation is still an approximation, since experience shows that the initial CB velocity should be part of the equation.

It is also true that the snooker balls would acquire more spin, simply because the initial CB velocity for both cases are the same. If the CB velocities scale with the radii of the balls, then the amount of spin would be constant.
 
A few months ago, I cracked open a brand new, factory sealed, set of Super Pro Aramiths. IOW, they were "clean." They transfered far more spin than the older or "dirty" pool room sets I usually played with.

When I use to play in the US Open 1pocket event in Kalamazoo, they used very clean Rashig balls. This was a very makable shot with those balls:

START(
%AD2N8%BL8P7%CJ7O4%DL8N2%EM7P1%FK7P1%GK7N8%HM7N8%IL7O4%JK8M6
%KJ7P7%LJ7N2%MK7Q3%NJ7Q9%OJ7M0%PG4H1%WE9Z7%XD3O3%YD8M6%ZG0I0
%]D1D2%^F0[1%eA6a7
)END

Lou Figueroa



Ronoh said:
It takes time for folks to understand that "friction" is the key. I agree with you whole heartly Cuetechasaurus.
 
mikepage said:
I think there are *three,* (not two) relevant numbers that characterize cloth. First is the table speed, which has to do the rolling resistance and can be thought of as a pseudo frictional force. (Is the cloth fast?)

The second is the ball-cloth friction, i.e. (Is the cloth slick?)

These are the two people talk about. The third has to do with how fast sidespin is wiped off. I think this one may be related to the other two, but I don't think it's a simple consequence of either one.

mike page
fargo
I believe your second and third cloth characteristic are exactly the same; they both entirely deal with ball-cloth friction. When you try to spin an object ball in place, the thing that slows it down is ball-cloth friction.

The first cloth characteristic that you mentioned (table speed) has little to do with "friction", but more to do with the elasticity of of the cloth. The more elastic the cloth, the faster the cloth is. Just try to imagine rolling a pool ball on a marble floor compared to rolling the ball on the surface of a bed. Assuming both balls have natural roll, then the friction of the two surfaces have little to do with the balls reduction in speed. The deceleration of the balls is dominated by the elasticity of the surface, or by how much the surface gives way.

Therefore, there are only two things that characterize a cloth: ball-cloth friction and cloth elasticity.

When you hit the CB with both forward and side spin, the net rotation of the traveling CB is just a supperposition of forward roll (axis of rotation is parallel to cloth surface) and side spin (axis of rotation is perpendicular to cloth surface). The first cloth characteristic only affects the forward roll component, and the second component only affects the side spin component.
 
I think the spin transfer is there, but it's heard to be only a couple of per cent, meaning that only one 50th of the amount of spin on the cueball will transfer to the object ball. The famous shoot with draw and follow in the object ball through a blocking ball is mostly because the object ball is rolling on the impact with the blocking ball, not because you imparted draw on the cueball.

Check out these shots, on which shot it's more difficult to make the stripe through the solid ?

#1
START(
%AD0Z4%OD6X6%PG0L9
)END

#2
START(
%AD0Z4%OE9Q1%PG0L9
)END

The key in these shots is not the spin you put on the cueball but the speed you use to make the stripe. Also, a worn cloth will help. With brand new cloth, shot #1 is almost impossible.
 
jsp said:
I believe your second and third cloth characteristic are exactly the same; they both entirely deal with ball-cloth friction. When you try to spin an object ball in place, the thing that slows it down is ball-cloth friction.

Imagine a ball sliding on two different surfaces for which it has exactly the same friction coefficient. One is hard rubber, like you might find on a weight-room floor, and the other is a low pile carpet. Now spin a ball on each of these. It is, as you say, the same frictional force that rubs off the spin in each case. But for the rubber case, the contact area is small and the frictional forces are all very close to the base of the ball, where they lead to very little spin-rubbing-off torque. For the carpet, the contact area is larger, and enough of the frictional force is far enough away from the base of the ball to provide some torque.

So the surface area of contact doesn't matter for linear sliding, but it does matter for sidespin sliding.

jsp said:
The first cloth characteristic that you mentioned (table speed) has little to do with "friction", but more to do with the elasticity of of the cloth. The more elastic the cloth, the faster the cloth is. Just try to imagine rolling a pool ball on a marble floor compared to rolling the ball on the surface of a bed. Assuming both balls have natural roll, then the friction of the two surfaces have little to do with the balls reduction in speed. The deceleration of the balls is dominated by the elasticity of the surface, or by how much the surface gives way.

Therefore, there are only two things that characterize a cloth: ball-cloth friction and cloth elasticity.

The first of these gives the slickness of the cloth.
The second of these gives the speed of the cloth.
The spin-rubbing-off is, imo, based on some unknown-to-me combination of the two.


mike page
fargo
 
mikepage said:
Imagine a ball sliding on two different surfaces for which it has exactly the same friction coefficient. One is hard rubber, like you might find on a weight-room floor, and the other is a low pile carpet. Now spin a ball on each of these. It is, as you say, the same frictional force that rubs off the spin in each case. But for the rubber case, the contact area is small and the frictional forces are all very close to the base of the ball, where they lead to very little spin-rubbing-off torque. For the carpet, the contact area is larger, and enough of the frictional force is far enough away from the base of the ball to provide some torque.

So the surface area of contact doesn't matter for linear sliding, but it does matter for sidespin sliding.
Good point. You're right, it is a combination of the two. Thanks for opening my eyes. :)
 
hanisch said:
(i would be interested in seeing the equations you came up with from your earlier post.)
If you're still out there somewhere William, sorry for the delayed response. Didn't mean to stiff ya. I've been a little busy and debating how much background info I should supply, if any. I decided to include a bit of it, which would make for a long post, so here it is in notepad form. The notation is a little clunky (no subscripts), but I think (hope) it's clear enough. If you've lost interest by now, I surely understand. :) (If you're still curious, Colin, this is for you too.) Don't be insulted by the background stuff, it's there for completeness (if you should look at it at all).

http://ww2.netnitco.net/users/gtech/InducedSpin.txt

(It needs to be viewed with word wrap invoked.)

hanisch said:
first, let's agree that a rolling ball means that it travels one circumference when it rotates along the horizontal axis (i.e. forward spin) once. if it travels more than one circumference when it rotates once, then it's "under spinning." if it travels less, it's "over spinning." when it's rolling, as opposed to under or over spinning, it's grabing the cloth more, i think. this is admitedly vague; perhaps you can state it more precisely. it's this grabbing that, if true, is causing any side spin to dissipate more quickly. there are other effects of a rolling ball that go unnoticed by many players (i think), which may add some insights to this.

for instance when a cue ball is rolling when it hits an object ball with, say, a half ball hit, it will follow earlier than if it's over spinning. that is, an over spinning ball will travel along the tangent line (or close to it) longer than a rolling ball, before it follows forward. most people, i believe, think that it's speed alone that determines this, but i think whether it's rolling or over spinning has more to do with it. note that a ball can be either rolling or over spinning at many different speeds. it starts to move forward when the speed and forward spin match, so to speak. when it "fully grabs," it's matched.

i hope you can add some further insight and analysis to this, whether i'm right or wrong.

william

Thanks for the explanation, as requested.

I don't think the ball actually grabs the surface more at natural roll. Picture a pinion gear rolling along a horizontal rack type gear. And imagine that there's no friction between the teeth. There will be no friction, period, then. But suppose some brake is applied that prevents the pinion gear from spinning as easily. The momemtum of the gear will want to continue moving it forward, but the pinion's teeth will now push up against the rack's teeth. This would be "grabbing" and is akin to static friction, the kind that anti-lock brakes try to acheive. If the teeth were not strong enough and began sheering off, the friction force would be reduced, and this would be like sliding friction. Sliding (dynamic) friction is generally less than static friction.

The rolling resistance a ball experiences from the cloth is much less than sliding friction. It arises, according to Ron Shepard, from the fact that a ball pushes down and compresses the cloth fibers ahead of it. The fibers behind it don't oblige by decompressing in time to restore the ball's lost energy from the work done on the fibers in front of it. I suspect you're right about the ball losing more spin when rolling though. A ball sitting in place would, I think, tend to drill itself a little dimple of compressed cloth and would probably experience less resistance than when it's encountering fresh fibers continuously.

I agree with everything else in your original post (again, for what it's worth), and that you're explanation for why some players might deny the fact of induced object ball spin to be quite plausible.

Jim
 
pinkisntwell said:
... many people think that if you hit the cb with english and it touches an ob the english is transferred to the ob (with reverse rotation). He then goes on to say it's a complete myth and to prove it ...
Of course he's wrong as he has since discovered. He should have realised he was on shaky ground when he disagreed with Walter Lindrum about transferred spin.

Some people have said that it's very hard to see the effect of transferred spin on a snooker table. That's false. Here is a demonstration shot:

Two feet from the top cushion, freeze three red balls sticking straight out from the side cushion and then freeze the pink at the end. Remove the three red balls. You now have the pink exactly three balls distance from the side cushion. In baulk on the same side of the table, freeze the three red balls just as before, perhaps one foot from the bottom cushion. It is possible to bank the pink off the bottom cushion back to the top pocket it is nearest -- white is placed for about a half-ball contact on pink, and no side is needed.

This is an excellent shot to win money from players who have read the wrong books. It has to be played with enough speed to keep the side on the pink clear to the bottom cushion. Usually, more than one try is required.
 
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