Thurs-Demo: The one with a Slinky

Today's demo: P and S-wave propagation using a slinky. When talking about earthquakes, it's often hard for students to "see" the relative motion of energy through rocks. We often use a slinky or a large spring to demonstrate the behavior of waves moving through a solid material. Trouble is, the movement of the wave is so fast, it's sometimes hard to see. What better way to slow things down than with the high-speed camera?

I haven't done any motion tracking, but I don't think the pressure wave is traveling any faster than the transverse (shear) wave in the spring - I think the spring is too "springy" so there's no discernible difference in velocity between the two.

Bonus Thurs-Demo: The One Dropping a Slinky

Have you ever dropped a slinky? If you've never looked closely at a free falling slinky, well you've come to the right place. But dropping a stretched slinky doesn't do what you might think. Take a look at the high speed:


Rhett Allain went so far as to build a computer model of a falling slinky to illustrate why the bottom of the slinky doesn't move until the top catches up. (Down?)