Prof. Walter Lewin, of the Dept. of Physics at MIT, derives the wave equation for a string and explains its consequences.

This clip was taken from the Prof. Lewin's class "8.03 Vibrations & Waves" and can be found at:
http://ocw.mit.edu/OcwWeb/Physics/8-0...

The complete version of this specific lecture can be viewed at:
   • Video