The game of ping pong, or table tennis, originated in England in the 19th Century. Around the same time, the de Laval nozzle, an hourglass tube used to accelerate a hot, pressurized gas to supersonic speeds was also invented. But it took a 21st Century mechanical engineer to put the two together. The result is a cannon capable of launching a ping pong ball at speeds of over 900 miles per hour — about Mach 1.2. It’s so fast that the lightweight ball blows a hole right through a paddle.
Gizmag has a good explanation of how Mark French, a mechanical engineer at Purdue University in Indiana, and his graduate students Craig Zehrung and Jim Stratton built the de Laval tube:
In the simplest cases, these guns consist of an open-ended tube (usually PVC plumbing pipe) into which a ping-pong ball fits loosely. The tube is sealed at each end by a membrane strong enough to withstand atmospheric pressure, and the air in the tube is removed. To fire, the gun is mounted so that the ping-pong ball is near the rear membrane, which is then nicked (typically by a knife or sharp point). The ping-pong ball is accelerated by the inrush of air, which also blows out the front membrane.