Written by William Gerstell | Published 8:25 PM, November 4, 2015

World-class table tennis players can hit the ball at a speed of nearly 70 mph. In my experience, returning the ball at this speed is very difficult. Imagine shooting four times faster in one shot-can even the best player make a shot? To find the answer, I designed a table tennis cannon that can shoot the ball at a speed close to half the speed of sound.

The power of a cannon comes from Boyle's law, which (simplified) says that pressure is inversely proportional to volume. For example, if you put air in a small container under a lot of pressure and then release it into a larger container—such as a gun barrel—the pressure will drop. This causes the volume of air to expand immediately, shooting out any objects, such as bullets, to share the space.

Boyle's law is also used in one of the most important air guns ever: the expedition air rifle. It was used by the Austrian army at the turn of the 18th century, but was widely known as a weapon carried by Meriwether Lewis during the Lewis and Clark expedition in 1803-06. His rifle can still be seen in the Virginia Military Academy Museum today.

I used PVC pipes to make my own views on Lewis weapons. A short section of pipeline is used as a gas storage tank. A sprinkler valve, which sells for about $15 at a hardware store, controls its opening. I connected the top cover of the valve to the blow gun attachment of the air compressor. Then I used a bicycle pump to add air to pressurize the water tank. When I pull the spray gun stem, it opens a port in the spray valve, allowing air from the high-pressure air tank to enter the longer PVC pipe used as the gun barrel. As the gas expands, it will pop out a pre-installed ping pong ball.

Using a ballistic chronograph to measure speed, I recorded speeds exceeding 300 miles per hour. So can a great table tennis player really return the ball at this speed? I recruited a volunteer and pressurized the cannon-watch the final video to see what happened.

This device can shoot ping pong balls at high speed and is not difficult to build. I don't recommend that you really try to incorporate it into your table tennis practice unless you readjust the air pressure. For example, if the pressure in the pressure accumulator exceeds 10 psi, when it fires, you don't want to get close to the shooter's muzzle end.

(5 ft) 1½ inch diameter PVC pipe (1) 1½ inch socket fitting (2) 1½ inch socket X 1 inch female thread reducing bushing (2) 1 inch NPT enclosed iron pipe fitting (1) 1 inch in-line sprinkler Valve (1) Compressed air palm blowgun (make sure you purchase a ¼ inch NPT air connection) (18 inch) 3 inch diameter PVC pipe (1) 3 inch sleeve type PVC end cap (1) 1/4 inch NPT Tank valve (1) 1/4 inch NPT 0 to 60 psi pressure gauge (1) 1/4 inch diameter NPT brass hex or common connector, 1 inch long, 1 piece of packing tape vinyl or aluminum tape ping pong ball

Sprinkler valves are used in lawn irrigation systems.

This article was originally published in the November 2015 issue of Popular Science, with the title "I built a 300 mph table tennis cannon."

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