Whack-a-stick discovery.

This flash animation is a powerful simulation of the longitudinal vibration of a solid beam (the basic physics behind modern non-destructive methods of testing timber battens to measure stiffness and predict strength. You can see the effect of striking the end of the batten with a hammer and see how it is possible to measure stiffness by the two methods of "time of flight" and "resonance". When you hit the batten you will see how the movement and pressure (the sound) moves along the batten, and reflects off the ends.  The simulator has lots of other controls and outputs you can experiment with.