I was playing pool...

[BobbyJoeCool]

And I realized that the cue ball wasn't doing what I thought physics said it should. So obviously I have the physics wrong. I know that if you hit the ball slightly to the left of the center produces a spin on the ball. As you look at the ball from the point where you hit it, it spins from right to left. Now, this should make the ball go to the right of the straight line of where it's hit, right? But, it keeps going left, hits the side and then produces this weird drag on the ball.

 

I guess I don't understand the physics of side spin on a pool ball. Can someone enlighten me?

[MetaFrizzics]

(1) The spin will not be perfectly vertical. Therefore, depending upon the tilt, there will be a pull or curve caused as the ball 'rolls' on the spinning end. Think of how spinning tops wander on a table-top.

 

(2) There is also drag and build-up of air in front of the ball from the direction of the spin as it moves along the horizontal trajectory. As with a golf-ball, there are some aerodynamic effects that depend upon the friction coefficient of the surface-to-air contact and the velocity of the ball.

 

(3) Some of the spin of the first ball will be imparted to the second ball through the friction of contact. Again a difficult effect to measure without laser measurements, and stop-action film.

 

(4) Small variations in friction between the balls and the felted top, effecting direction and transfer of forces/energy.

 

(5) A large part of the effect imparted to the second ball is based upon the 'spin' or 'English' on the first ball, controlled by the angle of strike, the amount of chalk, and the condition of the leather pad on the cue. Consult a billiards expert on this effect. It is controllable and in fact the main tool for controlling the behaviour of the second ball.

 

I hope this helps you understand the complex behaviour of billiard balls in real life.