I found myself logging onto merlot during a whole-class lesson today on earthquakes and volcanoes and I quickly searched for an activity on P and S waves. This is the one that I used and it was definitely instructive. By the end of the lesson, the students completely understood the differences between the two waves, but the classroom management end of it kept getting in the way. The students I work with are not used to getting out of their chairs. I think the advantages of using this interactive activity is that it helps students understand what would otherwise be an obscure process below the Earth. I found myself supplementing the activity with some animations online of the compression and shear motion through solids, and that was helpful as well. The students later revealed that they had fun getting out of their chairs and moving around while also learning something.