# Rigid Body Dynamics: balls colliding

1. Dec 17, 2011

### AndersLau

1. The problem statement, all variables and given/known data
I want to analyse two colliding balls, rolling flat on a billiard table.
I have recorded two collisions from above the table. A 1D collision and a 2D collision.
In both collisions only 1 of the balls are rolling before the collision.

Known is:
mass of the balls: m1=207g, m2=203g
their radius: r=3cm
friction between table and balls: F1=0.47N, F2=0.46N
The velocity of the balls right before and after the collision.

I'm supposed to be using some physics on rigid body dynamics. From the video you can see, that even though the collision is in 1D, the rolling ball keeps rolling after it has hit the other. My 1 question is, does the rolling ball transfer all of its translational energy, and keeps all the rotational itself? Or how does it work?

In which other ways could i analyze these situations?

Thank you.

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Last edited: Dec 17, 2011
2. Dec 17, 2011

### PeterO

In a normal billiards game the cue ball certainly retains its rotational momentum after collision. In that way the [very] skillful player is able to cause the cue ball to move to just about any position they wish, after striking the other ball.

Even less skilled amateurs can use back spin, top spin and side spin to make the cue ball jag off in a desired direction - including coming back towards the player.
Indeed it takes a fair amount of skill to ensure the cue ball has no spin at all when it strikes the target ball.

3. Dec 17, 2011

### AndersLau

okay, thank you.
Do you have any relevant calculations in mind? I find it a little tough.

4. Dec 17, 2011

### PeterO

Not really - though conservation of momentum says that without a head on collision, the cue ball can't stop completely.

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