All courses › Foundations of Physics › Free fall

Free fall

Without air resistance, every body falls with the same acceleration, the gravitational acceleration $g$ , straight downward. This holds regardless of mass: a rock and a feather would fall together in a vacuum. Free fall is therefore just a special case of the equations of motion with $a = g$ .

v = v_0 + gt

speed during the fall

h = v_0t + \tfrac12 gt^2

distance fallen

Symbols

$g$	gravitational acceleration	9.81 m/s²
$h$	distance fallen	m
$v_0$	initial speed (0 when dropped)	m/s

Example

A rock is dropped from rest. After $t = 2.0$ s it has fallen $h = \tfrac12\cdot 9.81\cdot 2.0^2 \approx 19.6$ m and has speed $v = 9.81\cdot 2.0 \approx 19.6$ m/s.

Choose the positive direction first (often downward), and then use

g

with a positive sign in the formulas.

Practise motion for free →

← Equations of motion · Projectile motion →

Part of Foundations of Physics: Motion.