"Andrew Coppin" <orp### [at] btinternetcom> wrote in
news:3f92fc25@news.povray.org: 

> [...]
> Mmm... the rotation doesn't quite seem right though... I can see at
> least one ball rotating in the opposite direction to the way it's
> rolling... (Well, I suppose it might be possible on ice ;-)
> [...]

Really?  Which one?  There is slippage allowed on the felt table, so if a 
ball has received angular momentum from other balls and it falls on the 
felt, the torque will not translate into instantaneous velocity or vice-
versa.  Although I just made up the friction coefficients for the pool 
balls.

Think of a cue ball.  If you hit it very low, it will backspin while 
still moving forward, it will slip on the felt, slowing down, until it's 
velocity and angular velocities eventually match, then it will roll (or 
probably hit a side before then).  Same with a ping-pong ball, if you 
press on it with your finger, it will move away from you while spinning 
in the opposite direction (it may even come back).

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