A Moment of Science

How Do Skydivers Control Their Terminal Velocity?

A skydiver's body is in a delicate balance. Gravity tugs her downward with a constant, relentless force, while air resistance pushes her upward.

sky_diver

Photo: Paul Sapiano

When a skydiver opens her chute, she's increasing the amount of surface area she presents to the ground dramatically.

A skydiver’s body is in a delicate balance. Gravity tugs her downward with a constant, relentless force, while air resistance pushes her upward.

The faster she falls, the more air resistance there is, so eventually these two forces cancel out. Then she falls at a constant rate, her terminal velocity.

Terminal Velocity

To link up with other skydivers in mid-air formations, skydivers need to control their terminal velocity very carefully.

After all, if you’re falling at a hundred and ten miles per hour, and your friend is falling at a hundred and twenty, there’s no way you can link at all.

How To Determine Your Terminal Velocity

As it turns out, your terminal velocity is determined by exactly two things–your weight, and the amount of surface area you expose to the ground. While a skydiver can’t do anything about her weight mid-fall, she can control how much area she presents downward.

Stomach down, with arms and legs spread out in a kind of belly-flop, the average skydiver is likely to fall at around a hundred and ten miles per hour.

Controlling Velocity

By bending arms and legs or angling her body–presenting more or less surface area to the ground–she can change her rate of fall, slowing or speeding up her terminal velocity around ten or twenty miles per hour.

To fall as fast as two hundred miles per hour, a skydiver goes into either a diving or a standing up posture. This presents the least surface area downward, so her terminal velocity is highest.

How Skydivers Land

When a skydiver opens her chute, she’s increasing the amount of surface area she presents to the ground dramatically. Her terminal velocity slows enough for a soft landing.

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