When an object moves in a circle at a constant speed its velocity (which is a vector) is constantly changing. Its velocity is changing not because the magnitude of the velocity is changing but because its direction is. This constantly changing velocity means that the object is accelerating (centripetal acceleration). For this acceleration to happen there must be a resultant force, this force is called the centripetal force.
When an object moves in a circle the centripetal force (F) always acts towards the centre of the circle. The centripetal force can be different forces in different settings it can be gravity, friction, tension, lift, electrostatic attraction etc.
To keep an object moving in a circle the centripetal force will need to increase if;
- the mass of the object gets bigger
- the speed of the objects around the circle gets greater
- the radius of the circle the object is moving in gets smaller