There is a tradition at my school of physics and chemistry classes having a day of science-related demos on Halloween (or the closest school day). We share and discuss a wide variety of demonstrations with the students that relate to topics they have already studied, topics they will be studying, or just cool stuff that, for whatever reason, we won’t study.
One of my favorite demonstrations involves a PVC pipe, a ping pong ball, a soda can, and a vacuum pump. The ping pong ball is inserted into the PVC pipe and both ends of the PVC pipe are sealed with mylar (the shiny material of some helium balloons) and PVC couplings. The vacuum pump then evacuates the PVC pipe. Once evacuated as much as possible, a knife tip breaks the seal at one end of the PVC pipe and the ping pong ball is pushed out the other end at an incredible high speed. Last year, we captured the result with a high-speed video camera (1000 fps):
This demo provides a great shared experience to later relate to almost any area of mechanics. I can use it as an example for the work-energy theorem with my regular physics class, fluids with my advanced physics class, or challenge the AP C class to solve for the force on the ping pong ball given the pressure applied to the hemisphere. Plus, we now have a whole collection of decimated soda cans on display!