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Moment

A moment is a force's ability to turn something about a point. The larger the force and the longer the arm, the larger the turning effect. The arm is the perpendicular distance from the point to the force's line of action.

M = F \cdot d

moment about a point

M = F\,d\sin\alpha

when the force is not perpendicular to the arm

Symbols

$M$	moment	Nm
$F$	force	N
$d$	arm, perpendicular distance	m
$\alpha$	angle between arm and force	°

Example

A 0.25 m wrench with 80 N perpendicular at the end:

$M = 80 \cdot 0.25 = 20$ Nm.

Choose a sign convention once (e.g. counterclockwise = positive) and stick to it for the whole problem.

Practise statics and equilibrium for free →

← Force components · Equilibrium →

Part of Statics and Dynamics: Statics and equilibrium.