New Scientist recently featured an article about a wingsuit flyer who plans to be the first to land from a freefall jump without a parachute. A wingsuit increases the jumper’s cross-sectional area so there is more air resistance (drag) and so he falls more slowly. If he is sufficiently skilful he can perform aerial stunts such as swoops and dives. The problem is that he is not able to fall slowly enough to land safely. One idea is to build a huge aerial slide that would break his descent slowly bringing him back to earth more gently.
The force that is bringing him to the ground is gravity and on Earth that is about 10 Newton per kg (N/kg). So every kilogram of his body is being pulled towards the earth with a force of 10N. This causes him to accelerate. The faster he travels, the greater is the air resistance opposing his fall. If an object’s speed through air doubles, then the air resistance quadruples so the forces quickly become balanced. When the air resistance is also 10N/kg, he falls at a constant rate. This is called terminal velocity. A wingsuit increases air resistance resulting in a lower terminal velocity, but still one that is too dangerous for landing so wingsuit flyers have to use a parachute for landing.
The parachute has to be opened soon enough that they can slow down before landing – leave it too late and they still hit the ground too hard.
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