Fairground rides whirl you round in circles and make your head spin. But you don't need to go to a fairground to see objects moving in circles.
- A vehicle on a roundabout or moving round a corner
- A satelite in orbit over the earth
- An athelete throwing a 'hammer' or a discus spinning after it has been thrown
For an object moving at a constant speed, at any instant:
- The object's velocity is directed along a tangent to the circle
- Its velocity changes direction as it moves round
- The change of velocity is towards the centre of the circle
The object therefore accelerates continuously towards the centre of the circle.
Any object moving in a circle must be acted on by a resultant force that acts towards the centre of the circle.
We say the resultant force is a centripetal force because it always acts towards the centre of the circle.
- The centripetal force on a vehicle moving round a roundabout is due to friction between the tyres and the road.
- The centripetal force on an aircraft circling round is due to the combined effect of its weight and the lift force on it. The entripetal force is the resultant of these two forces.