Re: phase vs group vel. and simulations

[Leigh Palmer <palmer@sfu.ca>]

> One example of using simulations was shown at the W13 workshop by
> Christian Wolfgang (last AAPT meeting). It was a collision of two
> balls (one initially at rest) on a flat surface. The question was:
> is such a collision possible? Students are expected to collect
> x(t) data and discover that the kinetic energy is conserved but
> the linear momentum is not conserved. A good show that a simulation
> may be highly unrealistic. But I see a value in this exercise.

Do you mean a collision between *rolling* balls? I think that is
the important distinction, and it is important to account for it
in the simulation. I would expect a result more nearly opposite
those described here, but neither quantity would be conserved for
balls rolling on a surface with friction.

Leigh