Fall (motion)

Basic physics

When only gravity acts, a body is in free fall and accelerates downward at about 9.8 m/s² near Earth's surface. In practical conditions other forces—most importantly air resistance—alter that motion. In a vacuum all objects fall with the same acceleration regardless of mass; this principle was illustrated in experiments derived from Galileo's work and in the famous Apollo demonstration of a hammer and a feather on the Moon.

Factors that change a fall

• Air resistance: drag grows with speed and surface area, reducing acceleration until terminal velocity is reached.
• Shape and mass: compact, heavy objects experience less deceleration from drag than light, broad ones.
• Buoyancy, wind, and lift: these can modify trajectories, especially for parachutes or gliding bodies.

Types and outcomes

Common categories include short drops (objects falling from furniture), long falls (from buildings or cliffs), and controlled descents (parachuting, rappelling). Terminal velocity varies by case: a skydiver adopts positions to change drag and control descent rate.

Uses and importance

Understanding falls is central in engineering (impact design, safety barriers), sports (diving, skiing), and science (measuring gravitational acceleration). Predicting impacts informs building codes, vehicle crash testing, and protective equipment design.

Notable distinctions

Colloquially "fall" can imply accidental descent; in physics it has a precise meaning tied to forces. Observations in vacuum, historical experiments, and modern high-speed measurements emphasize that gravity produces a uniform acceleration while environmental forces determine the observed motion.