1. Circular Motion
Motion of an object moving in a circular path

6. Centre
Radius = r
Diameter = d
Circumference = 2πr or πd
Period = T
Frequency = f

7. If the radius is 2 m, find the:
Circumference
Period
Frequency
Speed

8. Is the velocity constant?
Is the speed constant?
Is the velocity constant?

9. Centripetal Acceleration
An object in a circular motion is continuously changing its direction towards the centre.
Therefore the velocity is changing and there is an acceleration – which we call centripetal acceleration (towards the centre).

10. Centripetal Acceleration

11. Centripetal Acceleration is caused by Centripetal Force!!
Newton’s Laws of Motion state that: An acceleration is always caused by an unbalanced force (net force).
Centripetal acceleration is caused by an unbalanced force which continuously pulls the object towards the centre – which we call centripetal force.

12. Centripetal Acceleration (towards the centre)
Centripetal Force (towards the centre)

13. Do you see the centripetal force?

14. Do you see the centripetal force?

15. Do you see the centripetal force?

16. Example:
A car moves around a roundabout with the radius of 5 m. The car takes 12 seconds to go around in a complete circle. The mass of the car is 1.8 tonne.
Calculate the speed of the car.
Calculate the centripetal acceleration of the car.
Calculate the centripetal force acting on the car.

17. Question!
“What if the wire breaks?”

20. If the wire breaks…
The centripetal force will be removed, therefore there will be no centripetal acceleration – the object will move with a constant speed, in a straight path that is tangent to the circle.

23. PhET

24. Centripetal Force = towards the centre
Centripetal Acceleration = towards the centre
Velocity = tangent to the circle

25. WORKSHEET SEVEN (Circular Motion)
Textbook Activity 13A
Homework Booklet “Circular Motion”

26. The ball is moving at a constant speed of 5 ms-1
The ball is moving at a constant speed of 5 ms-1. Using a vector diagram, calculate the size AND the direction of the change in velocity of the ball between the two positions (A and B).

27. What would happen to Fc if:
the speed is increased?
the radius is increased?
the frequency is increased?
the period is increased?

28. Scott swings a 7kg hammer
Scott swings a 7kg hammer. Calculate the centripetal acceleration AND the centripetal force when:
Radius = 1.2 m, Speed = 6 ms-1
Radius = 1.2 m, Speed = 12 ms-1
Radius = 0.6 m, Speed = 6 ms-1
Radius = 1.2 m, Period = 0.7 sec