Purdue University professor Mark French has been using a subsonic ping pong gun to teach his students about physics. But why be subsonic when you can go supersonic? Not satisfied with propelling the balls a measly 400mph, French and his students recently built a ping pong bazooka that fires the balls at an astounding 900mph—135mph faster than the speed of sound—and shared video of the gun in action with Popular Mechanics.
"The [main] limitation here is how fast you can get air to go down the tube, because the ball is only going to go as fast as the air," French told Popular Mechanics. So he modified the gun with a convergent–divergent nozzle, which is more typically used to accelerate windflow in rocket engines and wind tunnels. Once the gun was up and running, they blew through plywood, VHS tapes, and paddles with ease; the projectile even dented steel. Traveling at supersonic speed, a ping pong ball has the same kinetic energy as a bullet—so it probably goes without saying that you shouldn't try this at home. But if you're curious about how French built the gun, head on over to Popular Mechanics for more details.