Practice

τ = rF Formula – Torque Practice

τ = rF — Torque when force is perpendicular (also τ = rF sinθ)

Torque (moment) measures a force’s turning effect about a pivot: τ = rF when force is perpendicular, or τ = rF sinθ in general.

Guide — how to use this formula

1. 1. Measure r from pivot to the line of action of F.
2. 2. Use τ = rF (⊥) or τ = rF sinθ.
3. 3. Opposite rotations get opposite signs.
4. 4. Static balance: clockwise τ equals counterclockwise τ.

Derivation

Only the component of F perpendicular to the position vector produces torque:

1. General form:
   \tau = rF\sin\theta
2. Perpendicular force (θ = 90°):
   \tau = rF

Convert cm → m for the lever arm. Balance: Στ = 0.

Examples

Example: r = 0.5 m, F = 40 N ⊥

τ = 20 N·m.

Example: find F

τ = 30 N·m, r = 0.5 m → F = 60 N.

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