1. 17 Motion in a circle
AQA Physics A level pp

2. Uniform circular motion
Speed unchanged
Speed = |Velocity| = v
Where r = radius and T = period
Velocity changes since direction is changing
Frequency = 1/T

3. Angular velocity, ω Rotational frequency f = 1/T
Angular frequency = 360o per second
We like to have simple units
We like equations without (too many) constants
Define So
Also

4. Radians Units of ω are radians per second
2π radians = 1 rotation = 360o
1 rad = 360/2π = o
Often c used in Maths but use “rad” in Physics
1 radian is also the angle which subtends an arc of a circle of length r, the radius

5. Centripetal acceleration
The change in velocity = acceleration time
Acceleration is perpendicular to motion
Speed is unchanged – only changes direction
Acceleration is always towards the centre of the circle
It is called the Centripetal Acceleration

6. Centripetal acceleration
Change in velocity
Change in position
But if is small
Also

7. Centripetal force
Force = mass x acceleration Force is in the direction of the acceleration

8. On the road – bridges and hills
If R=0 so only just holding road mg
Path of car

9. On the road - roundabouts
Friction provides centripetal force
If frictional force not enough, car continues in a straight line or curved path – not sideways!

10. On the road - banking
Banking provides a natural force – cars move in a circle!
Centripetal force
Reaction force

11. At the fairground – the big dipper
At the bottom of the dip
In this case...

12. At the fairground – the long swing
Like “Rush” at Thorpe Park
Potential energy
Kinetic energy

13. At the fairground – the big wheel
At the top
No force on rider due to chair
At the bottom
Maximum force on chair so feels heaviest

14. Ride safety Rides regularly checked for safety
Incidents investigated by HSE – Health and Safety Executive
G-forces experienced by riders
Max 1.9g into head
Max 5.1g into feet
Maximum g-forces on top are at the back on Stealth
Calculations for different sized
People

15. Orbits Real orbits Ellipses Sun is at a focus
Nearer the sun less Potential so more Kinetic energy
Force not completely perpendicular
Speeds up and slows down as well as changing direction

16. Your task... Use resources to understand these ideas
Text book
Internet
Resources on LVSpace
Other books
Create your own notes
Collect questions to challenge and develop your understanding
3-6 hours work...