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

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

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

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

5. Placing vectors tail to tail allows us to compare themVB VA VB B VA A

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

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

8. 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

9. …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

10. 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

11. 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

12. 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

13. 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)