freefalls

Free fall is the motion of a body where gravity is the dominant force; in an idealized vacuum the only force is gravity, yielding constant acceleration g. In Earth's atmosphere, air resistance and buoyancy modify the motion, so acceleration is less than g and can vary with speed.

Near Earth's surface, using a drag force F_d = 1/2 ρ C_d A v^2, the net acceleration is a = g − F_d/m. When drag balances weight, acceleration is zero and the object reaches terminal velocity v_t = sqrt((2 m g)/(ρ C_d A)). Terminal velocity depends on mass, cross-sectional area, drag coefficient, and air density; the orientation and shape of the falling body significantly affect A and C_d, influencing how fast it reaches and maintains terminal velocity.

Applications and examples: In physics, free fall experiments measure g or test gravitational models and the behavior of objects under gravity. In skydiving, the free-fall phase lasts until parachute deployment, with typical terminal velocities around 50–60 m/s for a belly-to-earth position and higher speeds in more streamlined postures. In engineering, controlled free-fall tests are used for drop testing of materials and equipment, and to study impact behavior and aerodynamics.