Research by scientists at Purdue University’s Department of Mechanical Engineering Technologies have developed what could be among the first supersonic ping-pong guns or ping-pong bazookas and have showed off just what it can do to a standard, wooden ping-pong paddle.
Although subsonic ping-pong guns had been developed before to demonstrate acceleration and the power of pressure differentials in air, the research paper states, a simple addition allowed the scientists to get the ping-pong ball to reach speeds of about 908 miles per hour (slightly more than Mach 1.2).
In a video explaining the concept, professor Mark French illustrates how a simple ping-pong ball gun is created with a piece of PVC piping that allows the ball to move a little but still fits it rather closely. Tape off the ends of the tube and create a vacuum through the bottom of it. Now, the tape is under stress, so it can be popped easily at one end. Then air rushes in with about 125 Newtons of force on the ball — that’s an initial acceleration of about 5,000 Gs, French explains. A little bit of air rushing in can get past the ball, creating pressure like a piston, French says, and then the tape on the other end breaks and the ball shoots out.
French describes the speed as “definitely subsonic but really fast for a ping-pong ball.” This gun can shoot the ball through two empty soda cans but not three.
The limitation, French points out, is how fast air can go down the tube.
“The ball can only go as fast as the air,” he says.
To make the air go faster, French uses a nozzle.
“If you add one more component to this — a convergent-divergent nozzle — [...] you should get supersonic flow here,” French speculates.
The new nozzle component is sealed to a compartment of pressurized air that will eventually break the seal on its own, sending the ball out the end of the barrel as it did before – except much faster.
French and his team tested this concept in the lab, but first they issue this disclaimer:
This is the result of the test:
Watch the concept explanation and the test for yourself (Note: the test comes at 5:47):
In their conclusion, the team stated that these tests don’t yet confirm the effect was caused by the nozzle. They write that more research will be conducted to confirm the nozzle is producing effect they think it is. They also speculate that changing the shape of the nozzle might impact the speed.