Download Section 10-4

Section 10-4
Newton’s Third Law
Newton’s Third Law
• When an object exerts a force on another
object the second object exerts a force of
equal strength in the opposite direction
– For every action there is an equal an opposite
reaction
Action – Reaction Pairs
• Baseball
– Ball hits the bat = action force
– Bat pushes back on ball = reaction force
– The bat makes the ball fly
• They don’t cancel each other out because each force is exerted
on different objects
• Two People Opening a Door
– One person pushes to the right – action force
– Another pushes door to left – action force
– Door pushes back in each direction equally
• The door doesn’t move because all forces cancel out
Momentum
• Called the “quantity of motion”
– Depends on the objects velocity and mass
– Momentum = mass x velocity
• Conservation of Momentum
– The momentum of any group of objects remains
the same unless outside forces act on it.
Conservation of Momentum Example