6.9 - Interaction Pairs
Newton's third law
- Newton's third law states that when two objects interact, the forces they exert on each other are equal in size and opposite in direction.
- These two forces are called an interaction pair.
The two forces in an interaction pair:
- Are the same type of force
- Are equal in size
- Act in opposite directions
- Act on different objects (one force on each, so they don't cancel out)
A hand pushing a wall and the wall pushing back are an interaction pair.
Examples
- Chair on the ground - The chair pushes down on the ground, and the ground pushes up on the chair with an equal and opposite force.
- Sun and Earth - The gravitational pull of the Sun on the Earth is equal and opposite to the pull of the Earth on the Sun.
TermDefinition
Newton's third lawThe law that whenever two objects interact, the forces they exert on each other are equal in size and opposite in direction.
Interaction pairA pair of forces of the same type that are equal in size and opposite in direction, acting on two different interacting objects.