How the physics works
Free fall: In a vacuum, every object falls at the same rate no matter its mass — height follows h = h₀ − ½gt² and velocity grows as v = gt. Try the Moon setting: this is the experiment Apollo 15 performed with a hammer and a feather.
Air drag: Air pushes back with a force that grows with the square of speed: F = ½ρCdAv². Light, large objects (ping pong ball) are affected far more than heavy, dense ones (bowling ball).
Terminal velocity: When drag grows to exactly balance weight, acceleration reaches zero and speed stops increasing — that's the flat line the acceleration graph approaches. vt = √(mg / ½ρCdA).
Bounces: Each bounce keeps a fraction e of the impact speed (the coefficient of restitution), so rebound height shrinks to e² of the previous drop. Dashed vertical lines on the graphs mark each bounce.
Reading the graphs: White dashed curves show ideal vacuum free fall for comparison. Up is positive, so velocity is negative while falling and acceleration sits at −g in a vacuum.