Aloha Edwin - been having a hard time teaching how waves move through various matter at different speeds (benchmark is using seismic waves to determine composition of Earth). If you run into any opportunities related to this please let me know. I have so many kids that just don't get it no matter how many strategies I use. Mahalo
Class Demo / Investigation Suggestion
Set up a glass baking dish with water. Drop a pebble. Have class make observations and time how long for the first wave to reach the side of the container. Then use a cornstarch water mixture and repeat the pebble drop.
The YouTube videos and online science simulations in the link below would support this demonstration well.
Have a look at the resources I have posted here: http://stempreacademy.hawaii.edu/subject/earthquakes
Let us know how this goes and if you discover other resources teachers may find useful. Thanks!