Quick Question about Physics of English

Dan White

Dan White

AzB Silver Member
Silver Member
I guess there's nothing "quick" when discussions of physics and pool get started, but here goes:

Let's say I put the cue ball on the head spot and aim at the foot spot. Now I shoot with follow and 1/2 tip left english. The cue ball rebounds and heads for the left corner pocket next to me. Set the shot up again and shoot with draw and 1/2 tip left english. Now the cue ball heads more towards the left side pocket rather than the corner (much more spin).

It seems to me this has something to do with spin/speed ratios being higher for draw, (conservation of spin while the cue ball slows more with draw than with follow, etc). Is it something like that, or am I just hitting it wrong? :)
 
One true fact. The more cue elevation employed with a given amount of off center hit the greater effect side spin will have.
 
All things equal (amount of english, speed, angle in, contact point on the rail, etc.), the follow should take a slightly wider angle, but if you hit with draw, the cue ball tends to curve more on its way to the rail effectively making the rebound slightly wider.

Try it again with the cue ball closer to the rail and the draw rebound angle should converge to or even become shorter than the follow rebound angle.
 
Dan White said:
I guess there's nothing "quick" when discussions of physics and pool get started, but here goes:

Let's say I put the cue ball on the head spot and aim at the foot spot. Now I shoot with follow and 1/2 tip left english. The cue ball rebounds and heads for the left corner pocket next to me. Set the shot up again and shoot with draw and 1/2 tip left english. Now the cue ball heads more towards the left side pocket rather than the corner (much more spin).

It seems to me this has something to do with spin/speed ratios being higher for draw, (conservation of spin while the cue ball slows more with draw than with follow, etc). Is it something like that, or am I just hitting it wrong? :)
Click to expand...

There's too many factors in your experiment to really determine anything. The speed of the shot, the amount of follow and draw, the precise amount of english, et cetera. Unless you can control all of those variables exactly, then you can't really come to a reliable conclusion.

With that said, in theory I think the shot should work exactly as you describe. The difference between the two shots is that the follow shot does not slow the speed of the cue ball as much, meaning the cue ball will swerve less. Also the follow shot will hit the rail harder, causing it to shorten up the rebound angle.
 
Dan White said:
I guess there's nothing "quick" when discussions of physics and pool get started, but here goes:

Let's say I put the cue ball on the head spot and aim at the foot spot. Now I shoot with follow and 1/2 tip left english. The cue ball rebounds and heads for the left corner pocket next to me. Set the shot up again and shoot with draw and 1/2 tip left english. Now the cue ball heads more towards the left side pocket rather than the corner (much more spin).

It seems to me this has something to do with spin/speed ratios being higher for draw, (conservation of spin while the cue ball slows more with draw than with follow, etc). Is it something like that, or am I just hitting it wrong? :)
Click to expand...
You're right - it's the difference in spin/speed ratios. It's also true that, as mentioned by some of the other posters, the cueball will curve more with draw. But the larger factor is the spin/speed ratio.

Jim
 
Dan White said:
I guess there's nothing "quick" when discussions of physics and pool get started, but here goes:

Let's say I put the cue ball on the head spot and aim at the foot spot. Now I shoot with follow and 1/2 tip left english. The cue ball rebounds and heads for the left corner pocket next to me. Set the shot up again and shoot with draw and 1/2 tip left english. Now the cue ball heads more towards the left side pocket rather than the corner (much more spin).

It seems to me this has something to do with spin/speed ratios being higher for draw, (conservation of spin while the cue ball slows more with draw than with follow, etc). Is it something like that, or am I just hitting it wrong? :)
Click to expand...
Ron Shepard explained this very well in his paper about pool physics. If you go through the physics which is what Ron did in this paper, it turns out that if you hit the cue ball over a long distance so that it is rolling smoothly on the cloth when it gets to the cushion, and consider how much side spin it will have in relation to its speed (which is called the "quality" of the spin), hitting with max follow and 1 tip of side spin is about the same as hitting on the equator and 3/4 tip of side or maximum draw and 1/2 tip. In fact the "line of constant quality" is a straight line from the base of the ball through those various points:
bob.gif
Pick out a diagonal line in the drawing on the right. Hitting anywhere along that line should give the same rebound angle off a far cushion.
 
Dan White said:
conservation of spin while the cue ball slows more with draw than with follow
Click to expand...

You answered your own question in your first post. The initial spin/speed ratio is approximately the same with draw or follow, but the draw will scrub the speed off without losing much of the side spin. Less speed, roughly equal spin = greater "juice" factor.

-Andrew

EDIT: If you watch much video of Efren Reyes, you can see him hit a lot of extreme side spin shots with a soft draw, even when the effect of the spin is to carry the CB forward off the rail (which intuitively seems like a follow shot), because what he's really trying to accomplish is maximizing his spin/speed ratio.
 
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Thanks everybody! Very interesting, especially Ron's image that Bob took the time to post.
 
Bob Jewett said:
Ron Shepard explained this very well in his paper about pool physics. If you go through the physics which is what Ron did in this paper, it turns out that if you hit the cue ball over a long distance so that it is rolling smoothly on the cloth when it gets to the cushion, and consider how much side spin it will have in relation to its speed (which is called the "quality" of the spin), hitting with max follow and 1 tip of side spin is about the same as hitting on the equator and 3/4 tip of side or maximum draw and 1/2 tip. In fact the "line of constant quality" is a straight line from the base of the ball through those various points:
View attachment 204754
Pick out a diagonal line in the drawing on the right. Hitting anywhere along that line should give the same rebound angle off a far cushion.
Click to expand...

That's interesting, I wasn't aware of that effect, but it makes sense.
 
Interesting read

http://library.thinkquest.org/TQ0013321/thescience.html

A elevated cue does not always give you the max spin(torque). Hitting the impact point on the CB at 90 degrees applies the most torque to get a ball spinning.

The spin can be along the vertical and horizontal center lines and anywhere in between. The cue can be spinning at 45 degree angle.

Something else to consider is the the force being applied has be to used for moving the CB and putting spin on the CB. So since there is only x amount of force applied, hitting a true center ball, all the force is used to move the CB and none for spin.

As you move farther away from center more force will be used for spin and not moving the CB.

FWIW
 
Dan White said:
Thread title: "Quick Question about Physics of English"
Click to expand...

Actually, with the complex math and technical jargon, most people have the opposite question -- "Quick Question about the English of Physics." ;)

J/K,
-Sean
 
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