A college professor explains how something so small and lightweight can be accelerated to hit supersonic speeds.
What does the Lockheed Martin F-35 Lightning II, a fighter jet that can weigh over 50,000 pounds, have in common with a Ping-Pong ball that weighs a mere 2.7 grams (0.00595 pounds)?
They can both break the sound barrier.
How is this possible?
It's all in the science, according to Professor Mark French of Purdue University, who created a cannon that can accelerate a Ping-Pong ball up to Mach 1.2, or 900 mph.
In an online video demonstration, French illustrates how it works. By placing ball into a PVC tube, sealing the ends with packing tape and then sucking all the air out of the tube, the ball — now in a vacuum — is set up to travel without any air resistance.
With air pressure from the outside on both ends of the tube, a simple slice or poke on one end of the packing tape allows air to rush in at atmospheric pressure. "What you wind up with is an initial acceleration of about 5,000 Gs," French said.
Since the ball doesn't fit into the tube exactly, a little puff of air gets past the ball. That air becomes compressed almost like a piston, and blows out the other end, breaking the seal and allowing the ball to come out at subsonic speeds.
But to reach supersonic speeds, a bell nozzle is added to one end of the PVC tube to allow for a supersonic flow through, French said. A compressor is then used to pressurize the nozzle until the seal breaks into the PVC tube, forcing acceleration of the ball to incredible speeds — fast enough to put a hole through the Ping-Pong paddle.
The idea behind this is very similar to how supersonic wind tunnels work, French explained.
It is important to note that that in a race, the F-35 Lightning II would win hands down against the Ping-Pong ball. The fighter jet can reach speeds of Mach 1.6, or 1,200 mph.
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