For example on a Ferris Wheel Circular Motion For example on a Ferris Wheel

To go round in a circle the pods on the ferries wheel are continually changing direction

Consider just two positions on the ride A and B B A

At A the pod has a velocity of VA At B the pod has a velocity of VB

Placing vectors tail to tail allows us to compare them VB VA VB B VA A

The difference between the two velocity vectors is the change in direction - ΔVAB VB VA This is the average change of direction of the pod between A and B and occurs halfway between them

This change in direction is always directed to the centre of the circle

Acceleration is the rate of change of velocity A change in direction is a change of velocity So although the pod is travelling around the ferries wheel at a constant speed… …it is continually Accelerating Since the change in direction is always towards the centre of the circle, so too is the acceleration

…the larger the acceleration The faster the ferries wheel rotates the quicker the rate of change of direction… …the larger the acceleration See Example The larger the radius of the curve the slower the rate of change of direction… …the smaller the acceleration

From Newton’s laws we know: To achieve an acceleration we need a resultant force The size of the acceleration is proportional to the size of the resultant force The acceleration is in the direction of the resultant force The size of the required force is proportional to mass of the object being accelerated

Therefore the size of the required resultant force increases when: The mass of the object is increased The radius of the circle is decreased ie. the tightness of the bend is increased The speed of the object is increased

This resultant force, however it is generated, is called… …the centripetal force Newton also tells us that there must be an equal and opposite to every force. In this case it is called… …the centrifugal force

It is the centrifugal force that we feel when we are flung to the outside of a bend as a car goes round it The body of the car or the seat push on us to make us go round the bend, providing us with a centripetal force While the centrifugal force doesn’t really exist, this effect can be used to test astronauts / pilots ability to withstand G-Force, dry clothes or separate the parts of blood in centrifuges (all be it different sizes)