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Torque
Beginner
Turning effect of a force.
τ = r×F = rF sinθTorque τ = r × F = rF sinθ is the turning effect of a force about a point. Larger lever arm gives larger torque; a force through the axis gives none.
A 20 N force perpendicular at 0.3 m on a spanner: 6 N·m.
Only the perpendicular component of force counts.
In more detail
Torque is the turning effect of a force, τ = rF sin θ, where r is the lever arm and θ is the angle between r and F. It is the rotational analogue of force.
Real-world uses
- A longer spanner gives more torque for the same push when tightening bolts.
- Engine torque determines how strongly a vehicle can accelerate from rest.
- A wrench works best when the force is applied at right angles to the handle, because the torque is then largest.
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Frequently asked questions
What are the units of torque?
Newton metres, though this is not the same as joules even though the units look similar.
Why does a force pointing at the axis give no torque?
Because the lever arm is zero, so there is no turning effect.
Why does a long wrench make it easier?
A longer lever arm gives a larger torque for the same force, so less effort is needed to turn the nut.
Related topics in Rotational Motion
Radians and degrees · Relation between linear and angular quantities · Rotational kinematics · Lever arm and moment · Equilibrium of a rigid body · Centre of mass of shapes