1. Forces
Newton’s Laws:
Law of Inertia states that an object will not move until a force is exerted
Law of constant acceleration- if a force keeps acting on the moving objects then it will accelerate
Conservation of Movement- For every action there is an equal and opposite reaction

2. What Is A Force? A force is a push or a pull
You have to push or pull doors to open them
Which do you do when you jump up?
Your legs push off the ground
Which do you do when you climb a rope?
You pull yourself up

3. What Units Are Forces Measured In?
The are measured in Newtons (N)
These units are named after
Sir Isaac Newton
Weight is measured in Newtons
There are 10 N in every 1 Kg
If my mass is 80 Kg how much do I weigh?
80 x 10 = 800 N

4. What Can Forces Do? They can change the speed of an object
They can change the direction an object is moving
They can change an objects shape
Which of these happens when you stamp on a coke can?
Change it’s shape
Which of these happens when you flick an elastic band?
You change it’s speed and it’s shape

5. Measuring Forces
Forces are measured using Newton meters (sometimes called Force meters)
These have springs inside them
This means that they can break if too much weight is put on them

6. Mass Or Weight Mass is how much matter we are made of
Your mass is the same everywhere you go
Weight is a mass being pulled by gravity towards the Earth
You are weightless is space
You would be six times lighter on the moon
You would be 10 times heavier on Jupiter
In all of these places you would have the same mass

7. Mass or Weight What is the astronauts mass on Earth? 120Kg
His mass on the moon?
120 Kg
His weight on Earth?
1,200 N
His weight on the moon?
200 N
Why does he weigh less on the moon?
It is six times smaller than the Earth, it has less gravity

8. Gravity This is when objects are pulled towards large objects
What does the Earth’s gravity do to us?
It pulls us towards the Earth
Why does the Earth go around the Sun?
The Sun’s gravity keeps us in orbit
Which would have more gravity; the Earth or the Sun?
The Sun because it is much bigger
The escape velocity of a rocket leaving the Earth is 11.2 km/sec (40,000 km/hour)

9. Galileo
Legend has it that Galileo took a canon ball and a wooden ball the same size to the top of this tower
He dropped them at the same time
Which hit the ground first?
They both hit the ground at the same time!
Leaning Tower of Pisa

10. Friction This happens when two surfaces rub against each other
It creates heat
It slows things down
How do bike brakes stop a bike?
The brake pad presses against the wheel until friction slows it till it’s stopped. The tyre of the wheel then rubs against the ground slowing the bike down, until friction stops it

11. Friction Why is friction useful to: Us when we are running?
Friction allows us to stop
The brakes in a car?
It allows the car to slow down or stop
Why is friction a nuisance if:
You fall on gravel?
You get burns or grazes
If you don’t oil a bike chain?
The chain will stop moving

12. Reducing Friction Engine parts and bike chains are oiled
This is called lubrication
This prevents wear and
tear
It saves money because
the engine does not have
to work as hard

13. Reducing Friction
Swimmers attempting long swims cover themselves in grease
Ball bearings can be used (e.g. in gear boxes)

14. Upthrust
This is the force that pushes things up when they are in water
It is a weak force
Polystyrene is full of air holes, this means it is light and can be pushed to the surface of a swimming pool
Why do steel ships float?
They are hollow (full of air) and have a large surface area for upthrust to push up

15. Thrust and Air Resistance
Thrust if a forward force
Air Resistance (drag) is when air particles slow things down
When would air resistance be a nuisance?
It slows down cars, aeroplanes, animals running etc.
When would it be useful?
Parachutes

16. This Ferrari GG50 is streamlined to make it go faster

17. Streamlining Reduces Drag
This bottlenose dolphin is streamlined to reduce drag in water

18. Force Diagrams Arrows show the direction of the force
Their thickness illustrates the size of the force
These two forces are balanced, the book is not moving

19. Force Diagrams Name the force that slows the car down?
Friction (and drag)
What should happen to the car?
It will slow down
400N
500N

20. Force Diagrams What will happen to this truck? It will stay still
It will move forward

21. Gravity 1

22. Gravity
Upthrust
They are equal

23. Gravity 5

24. Gravity
Upthrust
A is bigger than b 4