Torque is the turning effect of a force about an axis or pivot. In IB Physics HL, calculate its magnitude using , or equivalently , where is the perpendicular distance from the axis to the force's line of action.
Torque is the turning effect of a force about an axis or pivot. In IB Physics HL, calculate its magnitude using , or equivalently , where is the perpendicular distance from the axis to the force's line of action.
Torque depends on both the force and where and how it acts:
Therefore,
The SI unit is the newton metre (N m). Although this has the same base units as energy, torque is not measured in joules because torque and energy represent different physical quantities.
For example, a force acts at to a wrench, from its pivot:
The torque is greatest when the force is perpendicular to the lever, since . It is zero when the force acts directly toward or away from the pivot, since its line of action passes through the axis.
Torque also has a rotational direction. Choose a sign convention, usually anticlockwise positive and clockwise negative. The resultant torque is the algebraic sum:
For rotational equilibrium, .
A common misconception is that a larger force always produces a larger torque. This is incorrect: torque also depends on the perpendicular distance and the force's angle.
This is A.4 Rigid body mechanics, an HL-only topic. In calculations, identify the pivot, use the perpendicular distance or include , state your sign convention, and sum clockwise and anticlockwise torques correctly. Do not confuse with the perpendicular moment arm unless the force is perpendicular to the lever.