1. Imagine a ball… Draw the forces acting if: It is at rest on the ground
It is accelerating as it falls through the air
It is moving at constant speed in a circle

2. Draw the forces acting if: It is at rest on the ground –
Forces are opposite in direction and equal in magnitude therefore no movement is seen.
It is falling through the air
Forces are opposite in direction but are not equal in magnitude therefore a resultant force exists and the ball moves in the direction of resultant force.
It is moving in a circle
Tricky! Lets see why and then we’ll come back to your diagram

3. Misconception of the Week
Don’t confuse the idea of velocity (speed) and force when drawing arrows.
On a force diagram you don’t need to include the velocity – this is implied by the larger force

4. By the end of this lesson you should…
Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.

5. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Moving in Circles
Way back in year 9 or 10 you saw that acceleration doesn’t just mean speeding up.
There are 3 forms of acceleration
S_______ _____
C________ d_________

6. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Moving in Circles
Way back in year 9 or 10 you saw that acceleration doesn’t just mean speeding up.
There are 3 forms of acceleration
Speeding up
Slowing down
Changing direction

7. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Moving in Circles
Objects moving in circles can move with a steady speed, but they are constantly changing direction.
This means they are accelerating.
Newton’s 2nd law (F = ma) tells us that a resultant force is required for an object to accelerate.
For circular motion, this force is known as the centripetal force.

8. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Moving in Circles
The centripetal force always acts at 90 degrees to the direction of movement and therefore keeps the object moving in a circle about a fixed point.
Centripetal force is the name used for a force which makes objects move in a circle. It doesn’t tell you what created the force.
We do the same with the term ‘thrust’. Always moves objects forward but it can be produced by an engine, a magnet or even a hand!

9. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Identify the source of centripetal force in each case. Remember the centripetal force is always acting to keep the object in circular motion.

10. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Identify the source of centripetal force in each case. Remember the centripetal force is always acting to keep the object in circular motion.
Tension in the rope
Friction on the wheels

11. Draw diagrams to show three examples of any form of circular motion
Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
For your notes…
Draw diagrams to show three examples of any form of circular motion
Identify the centripetal force in each case

12. How does the radius of the circle affect the motion?
Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
How does the radius of the circle affect the motion?
Still not sure?
Watch the figure skater, what happens to the speed and as she pulls her body inwards.

13. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
The smaller the radius the faster the speed, what does this mean for the value of centripetal force?

14. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
What about if the mass of the body moving in a circle were to increase?
Give it a go, hold some heavier weights as you spin. What do you notice about the force pulling on your arms?

15. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Time 20 swings and then divide by 20 to reduce error. Change the length of thread (l) by moving the paper clip.
You will need to plot l against t so design a sensible table for doing so.

16. Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
Orbital Speed
orbital path
height
orbit time
communications satellite
above equator km
24 hours
weather satellite (NOAA)
over the poles
830 km
102 minutes
land surveying
320 km
90 minutes
Using 2πr to help you find the distance travelled calculate the orbital speeds for these satellites.
What is providing the centripetal force?

18. True or false? Spy satellites are placed in high Earth orbits
Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
True or false?
Spy satellites are placed in high Earth orbits
Once in orbit, a satellite requires no fuel
Increasing the distance above the Earth will increase the force on a satellite
Comets travel at a constant speed throughout their orbit
Halving the distance above the Earth will quadruple the force on a satellite

19. True or false? Spy satellites are placed in high Earth orbits
Learning Objectives
By the end of this lesson you should…
Be able to describe the forces acting on an orbiting satellite
Understand the term centripetal force
Describe some examples of circular motion and explain what provides the centripetal force in each example.
True or false?
Spy satellites are placed in high Earth orbits
Once in orbit, a satellite requires no fuel
Increasing the distance above the Earth will increase the force on a satellite
Comets travel at a constant speed throughout their orbit
Halving the distance above the Earth will quadruple the force on a satellite
false
true
false
false
true