Circular motion

An object attached to a string, like a yo-yo, will move around in a circular motion if whirled around in the air. For an object which is moving in a circular direction at a constant speed at any moment:

• – its velocity is continuously changing direction as it moves around in the circle
• – this change of velocity is towards the centre of the circle
• – the velocity is directed to the circle of direction along a tangent

This means that the object is constantly accelerating towards the centre of the circle. Therefore, the force being placed on the object acts towards the centre of the circle. This force is as a resultant force known as the centripetal force. This force always acts toward the centre of the circle.

Aeorplanes have a centripetal force which is the resultant force of two other forces:

• – the air plane’s weight
• – the lift of the air plane

A number of factors affect centripetal force. For example, take a remote controlled car.

• – If it’s moving too fast then it will simply skid off in a straight line. This means that the centripetal force must increase as the speed increases.
• – If the circle it’s moving in is too small then, again, it will skid. This means that as the radius of the circle decreases the centripetal has to increase.

Centripetal force is also affected by mass:

• – the greater the mass of an object, the greater the centripetal force