Ping pong guns are usually built from hard, colorful plastic, cast in candy colors that fit right in with the rest of the toys sold alongside them at drugstores and dollar marts. They're fragile. A good one might be able to propel a ping pong ball 10 feet a few dozen times--inevitably, the spring action punching the balls out of the barrel will break. Such is the life of the ping pong pop guns I grew up with, which makes me wish I'd known a mad scientist like Perdue University's Mark French--French and two of his mechanical engineering grad students built a ping pong gun that fires at about 900 miles per hour, aka more than Mach 1.
We're talking ping pong balls as fast as Russian MiG fighter jets. Fast enough to blow a hole straight through a paddle. On second thought, it's probably a good thing the pop guns I had as a kid didn't fire this fast.
French isn't actually the first to create a supercharged ping pong launcher. His gun builds on an existing concept that fired the lightweight balls at about 700 feet per second, or less than 500 mph. It's an incredibly simple design: the ping pong ball sits in a PVC tube which is sealed with duct tape on each end. When a nozzle is added to the tube and the air is sucked out, it creates a vacuum. And once there's a vacuum, popping the tape on one end will send a huge wave of air into the tube, blowing the tape out on the other end and shooting the ball down the barrel with "an initial acceleration of about 5000g," according to French.
His does it better. The professor made a great video that explains how these designs work; his gun actually takes inspiration from the nozzles in rocket engines, which are designed to create supersonic flow. Basically, French fills a container with pressurized air until it breaks its duct tape seal. That pressurized air is pushed through the nozzle into the ball's vacuum chamber, and we have lift-off. And boy, does that thing fly.
Mach 1.23, or about 930 miles per hour, is the ball's top speed so far. It's fast enough to blow through two empty soda cans and put a dent in a third. Perdue says not to try this at home--the scientist's equivalent of "you'll shoot your eye out"--but there's a real appeal to causing destruction with something that weighs a tenth of an ounce, or less than 3 grams.