All courses › Foundations of Physics › Weight and normal force

Weight and normal force

The weight is the force Earth pulls a body with, always directed straight down. The normal force is the force the surface pushes back with, perpendicular to the surface. On a horizontal surface with no other vertical forces the two are equal in size, but that is not true in general.

G = mg

weight

N = mg

normal force on a horizontal surface (no other vertical forces)

Symbols

$G$	weight	N
$N$	normal force	N
$g$	gravitational acceleration	9.81 m/s²

Example

A 40 kg crate rests on the floor. Its weight is $G = 40\cdot 9.81 \approx 392$ N, and since no other vertical forces act, $N = 392$ N.

Mass is the same everywhere, but weight and normal force depend on the situation – do not set

N = mg

without checking.

Practise forces and Newton's laws for free →

← Newton's laws · Friction →

Part of Foundations of Physics: Forces and Newton's laws.