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Q How do hovercrafts work?

— Will Swisher, Madison, Wis.

A Mike Randall, Wonders of Physics program at the University of Wisconsin-Madison:

To understand how a hovercraft works, we have to understand a few things about matter. We, and all ordinary matter, are made of little tiny things called atoms and clumps of atoms called molecules.

Air molecules are so small about 840 billion of them fit inside a ping-pong ball. They’re incredibly tiny, but collectively very powerful. On average those air molecules are zipping around at 1,100 miles an hour and fill up whatever space they’re given.

Think of the end of your thumb as about a square inch. On each square inch of the hoverboard, the air molecules collectively are exerting a force of almost the weight of a bowling ball, about 14.7 pounds per square inch.

That’s an enormous amount of force pushing from one side of the base, and yet nothing happens on its own. That’s because there are just as many air molecules pushing from the other side of the base, so the two forces cancel out.

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The basic components of the hovercraft used in UW-Madison’s Wonders of Physics program are an air blower that blows air underneath the board or platform, an air-tight fabric on the back side with a few holes around it and a plastic disc in the center to hold it together.

With the air blower, additional air molecules can be blown under the board — which means more collisions and more lift force underneath the board — as long as the air is contained.

A hovercraft has what’s called a skirt to contain the air. When the air blower is turned on, this skirt creates a pocket that traps the pressurized air. That pressurized air is what gives the lift to make a hovercraft work.

Blue Sky Science is a collaboration of the Wisconsin State Journal and the Morgridge Institute for Research.