Paper 2 · Moments and Equilibrium
Torque and energy share the same base-unit combination, kg m² s^-2. Why would it be inappropriate to measure torque in joules?
ATorque only exists in rotational systems, and the joule is defined only for translational (straight-line) systems.
BTorque is the turning effect of a force at a perpendicular distance, not a transfer of energy, so using the joule would wrongly imply that energy is being transferred.
CTorque and energy do not actually share the same base units once expressed in kilograms, metres and seconds, so the joule would be dimensionally the wrong unit for torque entirely, regardless of physical meaning.
DThe joule is defined only for electrical quantities, not for mechanical quantities like torque.
Explanation: Torque and energy are physically different: energy (work) is a scalar describing energy transferred, whereas torque is the turning effect of a force acting at a perpendicular distance, with no displacement in the force's own direction. Using the joule for torque would wrongly suggest it represents energy transferred.
Derived from ZIMSEC Physics Paper 2, November 2002, Q1