I don't know if the opening 'packets' animated gif would suit your purposes or not,
for demonstrating phase and group velocity.
The group velocity in that animation is greater than the phase velocity, as you
can see from the 'envelope' overtaking individual 'ripples' in the packet.
This comes up right away on my home page (below), and in a larger version
when you click on the Packets Page.
I'm not sure if I have the maple code in the packets for it. The place to look would
be in the 'waves' course. Let me know if you need more info.
--
Mike
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Mike Moloney moloney@nextwork.rose-hulman.edu
Dept of Physics & Applied Optics (812) 877 8302
Rose-Hulman Institute of Technology Terre Haute, IN 47803 http://www.rose-hulman.edu/~moloney