Here is my world famous sodium explosion video.  Over 1,000 pounds of sodium metal was treated on-site in 1987 by dropping it into a pond about 10 pounds at a time, with one big bang at the end.  Watch the sodium cannon at the end and see if you can figure out where we went wrong.  Hint:  never put an explosive in a container with one closed end and then aim the open end at your crew.  I was the senior chemist on-site at the time, and I actually came up with this idea, for better or worse.  Left a lagoon with a pH of 14, but the sodium metal was gone!

Build the amazing Cheap Physics Lenz's Law demonstrator to show that there is no such thing as a free lunch. A real crowd pleaser for under ten bucks. Video coming soon - but this will get you started.