Chutel

Meet Chutel, a skydiver who slows to a gentle drift when her canopy opens.

Moving through air means pushing air out of the way, which creates drag. The drag force grows with the square of speed, so going twice as fast means four times the drag. It also grows with the air's density, the frontal area and the drag coefficient, which depends on shape.

A falling skydiver speeds up until the drag equals their weight, then falls at a steady terminal speed. Setting ½ρv²C_D A = mg gives v = √(2mg / (ρC_D A)).

Take an 80 kg skydiver in air of density 1.2 kg/m³. Falling belly-down, with C_D A of about 0.5 m², v ≈ √(2 × 80 × 9.81 / (1.2 × 0.5)) ≈ 51 m/s. Under a canopy with C_D A of about 30 m², v ≈ 6.6 m/s, slow enough to land safely. These C_D A values are typical estimates, not exact.

Engineers shape cars, planes and bikes to lower C_D, saving fuel and effort. Cyclists tuck in to reduce their area.