Dynamics of Circular Motion

Having covered linear motion under Newton's laws, this final section turns to circular motion. A crucial distinction: linear motion can occur with zero force (Newton's first law), but circular motion never can — there is no "first law" analogue for circular motion; some force must always act to continuously bend the path into a circle.

In general, a force can change a particle's velocity in three distinct ways: (1) change only the speed, without changing direction; (2) change only the direction, without changing the speed — if this happens continuously, it is uniform circular motion; (3) change both speed and direction (non-uniform circular motion, e.g. a swinging pendulum, or a p …