3.6.1.1
No work is done during uniform circular motion
Circular Motion — AQA A-Level Physics
- The centripetal forceThe resultant force directed towards the centre of a circular path that causes an object to move in a circle. It is not a separate force but the net force providing circular motion. is always perpendicular to the direction of motion (velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.).
- Work $done = force x distance x \cos$ theta. When theta = 90 degrees, cos 90 = 0, so $W = 0$.
- Since no work is done, there is no change in kinetic energyThe capacity to do work. Measured in joules (J).The energyThe capacity to do work. Measured in joules (J). an object possesses due to its motion..
- The speed stays constant; only the direction changes.
Examiner Tips and Tricks
If asked 'why does the speed not change in circular motion?', the answer is: the centripetal forceThe resultant force directed towards the centre of a circular path that causes an object to move in a circle. It is not a separate force but the net force providing circular motion. is perpendicular to velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹., so it does no work and cannot change the kinetic energyThe capacity to do work. Measured in joules (J).The energy an object possesses due to its motion..