Freifall

Freifall is the motion of a body under the influence of gravity alone, or approximately so, with negligible other forces. In physics, it refers to the idealized case in which air resistance and other forces are neglected. In everyday conditions, air drag reduces acceleration and can lead to a limiting or terminal velocity.

In a vacuum or in a context where drag is ignored, the acceleration is constant and equal to g, about 9.81 m/s^2 near the Earth's surface. If released with initial position s0 and velocity v0, the position and velocity at time t are s = s0 + v0 t + (1/2) g t^2 and v = v0 + g t. Downward is often taken as positive in teaching.

When drag is present, the motion is governed by m dv/dt = mg − D(v), where D(v) is the drag force. For quadratic drag, D(v) = (1/2) ρ C_d A v^2, leading to a terminal velocity v_t = sqrt( (2 m g) / (ρ C_d A) ), where ρ is air density, C_d the drag coefficient, and A the cross-sectional area. Drag increases with speed, so acceleration falls toward zero as the object approaches v_t.

Historically, Galileo challenged the idea that heavier objects fall faster, arguing that, neglecting air resistance, all bodies accelerate equally. Newton’s laws and the law of universal gravitation formalized free fall. Measurements show g varies slightly with location and altitude.

Freifall concepts appear in applications such as parachuting, skydiving (the phase before parachute deployment), and spaceflight, where orbital motion corresponds to continuous free fall around a body, producing microgravity conditions for astronauts.