These pictures show some objects which move in circular paths. What other examples can you think of?

The answers to these questions lie in the nature of circular motion. Even if an object is moving at constant speed in a circle, its velocity keeps changing because its direction of motion keeps changing. Consequently the object is accelerating and so, according to Newton’s first law, there must be a force acting on it. The force required to keep an object moving in a circle can be provided in many ways.