Collisions
Newton's third law
• According to Newton's third law of motion,
whenever two objects interact, they exert
equal and opposite forces on each other.
• This is often worded as 'every action has an
equal and opposite reaction'. However, it is
important to remember that the two forces:
• act on two different objects
• are of the same type (eg both contact forces)
Examples of force pairs
• Newton's third law can be applied to examples
of equilibrium situations.
A cat sits on the ground
• There are contact gravitational forces
between Earth and the cat:
• the cat pulls the Earth up
• the Earth pulls the cat down
• These forces are equal in size and opposite in
direction.
Pushing a pram
• There are contact forces between the person
and the pram:
• the person pushes the pram forwards
• the pram pushes the person backwards
• These forces are equal in size and opposite in
direction.
Car tyre on a road
• There are contact forces between the tyre and
the road:
• the tyre pushes the road backwards
• the road pushes the tyre forwards
• These forces are equal in size and opposite in
direction.
A satellite in Earth orbit
• There are non-contact gravitational forces
between Earth and the satellite:
• the Earth pulls the satellite
• the satellite pulls Earth
• These forces are equal in size and opposite in
direction.
Video
• https://www.bbc.co.uk/bitesize/guides/zqs47
p3/revision/4