✓ Sources checked · 10 September 2026 · View verification
A rigid body in static equilibrium is at rest with both zero net force and zero net torque. Torque is a moment of force, τ = r × F, not another force.
By Matan · Updated
Lever arm and angle
The magnitude is τ = rF sin θ = Fdperp. Here r is distance from the chosen origin to the force application point; dperp is the perpendicular distance from the origin to the force’s line of action. Do not multiply a perpendicular lever arm by sin θ a second time. Torque is measured in N·m. [1]
Worked balanced beam
Neglect a beam’s mass and place a pivot between two downward loads. A 30 N load 0.40 m to the left gives a 12 N·m moment. A 20 N load 0.60 m to the right gives the opposite 12 N·m moment. Net torque is zero. The pivot must also supply 50 N upward for net force to vanish.
Balance and motion
Zero net force means zero centre-of-mass acceleration, not a prescribed nonzero constant acceleration. Static equilibrium additionally requires rest. The direction of torque describes the change in angular momentum; it need not be the direction in which the body is already rotating. A braking torque can oppose ongoing rotation. [1]
Check all conditions
A horizontal beam is not automatically balanced, and balancing torque alone does not prevent translation. Use a free-body diagram, choose an origin and state whether supports can actually exert the calculated forces. The example assumes a rigid beam and ideal support.
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How this article was checked
Sources checked; calculations checked where shown. The definitions, model assumptions and main explanatory claims were cross-checked against the sources below. Worked-example arithmetic and units were checked separately. These examples are illustrative calculations, not experimental measurements.
Source cross-check and editing assisted by AI. No independent human scientific review is recorded for this revision. The check applies to the version dated 10 September 2026; it is not a guarantee that every possible interpretation is correct.
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Sources and further reading
- OpenStax: Conditions for static equilibrium — Conditions for static equilibrium.
Cite this article
Matan. “Torque and Equilibrium.” Your Physicist. Originally published 2023-03-17; updated 2026-09-10. https://your-physicist.com/torque-and-equilibrium/
Revision history
: Corrected definitions of static and dynamic equilibrium and the lever-arm ambiguity; added force and torque checks. Added linked sources and a transparent verification record.
