Now, ping-pong gun that can fire ball faster than the speed of sound
London, Feb 6 : Researchers have developed a machine that could make a ping-pong ball travel at speeds greater than a supersonic F-16 jet screaming across the sky - all it takes is some sticky tape.
In a demonstration that Blue Peter presenters would be proud of, that's what a team of US researchers have achieved in their lab at Purdue University, Indiana, by modifying a ping-pong gun, the Daily Mail reported.
Mark French, a mechanical engineer at the university, and his graduate students Craig Zehrung and Jim Stratton, have shown off their customised ping-pong gun that can fire the balls at a speed of more than 400metres a second, or about Mach 1.2.
Professor French and his students wanted to develop a demonstration of how a de Laval nozzle (also called a convergent-divergent nozzle) converts subsonic gas flow into supersonic flow.
The scientists explain that the ping-pong gun is a popular and compelling tool for demonstrating acceleration and the power of pressure differentials in air.
"It has even proven to be a challenging problem for computational fluid dynamics since it encompasses a range of aerodynamic phenomena that are particularly difficult to model," French said.
"The design of the team's ping-pong gun is reassuringly low-tech. It consists of a pressure chamber sealed with several layers of duct tape," he said.
When the pressure exceeds about 620kPA, the tape bursts, allowing a pressure wave into a special nozzle - called a de Laval nozzle.
From there, the pressure wave rushes in to the barrel, which in turn shoots out the ping-pong ball at supersonic speeds.
The design of the de Laval nozzle is what creates the supersonic speed. The tube is pinched in the middle, making a carefully balanced asymmetric hourglass shape.
Designed in 1888 by Swedish engineer Gustav de Laval for use with steam turbines, the nozzle is also used in supersonic jet engines.
As the air enters the nozzle it accelerates as it is compressed. At the pinch, the air flow matches the speed of sound and then exceeds it, becoming supersonic as the tube begins to expand.
This supersonic flow then enters the gun barrel, where it accelerates a ping pong ball to supersonic speeds.
Having carried out their modifications, the team said that they measured the velocity of the ball using a high-speed video camera set to record at 16,000 frames/second with an exposure time of 1/128,000 second.