A constant net force perpendicular to the velocity of an object causes it to travel in a circular path. Such a force can be described as a __centripetal force__.

For an object moving at a constant speed in a circle:

Centripetal acceleration is given by: and

= yields: = ^{2} and

Circular motion can be investigated with __whirling bungs__: a bung is swung in a horizontal circle. A suspended weight remains stationary if the force it provides (i.e. its weight) is equal to the centripetal force required to make the bung travel in a circular path. By varying the weight and the angular velocity etc., properties of circular motion can be investigated. A glass tube is used (low friction) with a paperclip to ensure that the radius does not change.