I'm hugely amused by the efforts of a Purdue University professor to use fun and games as a method of teaching physics. Would you believe he's come up with what Popular Mechanics calls a '900-MPH Supersonic Ping-Pong Bazooka'?
For years, Mark French has been using the regular subsonic version of the gun to teach kids about physics.
. . .
On a hunch, French and his students modified the gun with a convergent–divergent nozzle, the type used in rocket engines and supersonic wind tunnels to accelerate air flow. The revamped gun shoots pressurized air through the hourglass-shaped nozzle. As the air travels through the nozzle's choke point, compression accelerates the air. It blasts the ping-pong ball outward at 900 mph (the speed of sound is roughly 765 mph).
. . .
Once the engineers got the bazooka up and running, they tested it on all sorts of materials, including VHS tapes, 3/4-inch plywood, stereo speakers, and even a sheet of steel. "The ball didn't go through the steel, but it put a whopper of a dent in it," French says. "Normally what happens is the ball comes out in pieces—it's shattered but not deformed. For this one, it melted and buckled. I didn't expect that."
There's more at the link. Here's a short video clip of the beast being test-fired.
A longer video presentation, giving more details, may be found here.
Kudos to Prof. Mark French for a very original teaching tool!