1. Conservation of Momentum In the absence of an outside force, the momentum of a system will remain unchanged. Momentum before = Momentum after p i = p f Ex: A bat hits a baseball- the bat exerts a force on the ball, the ball must exert an equal but opposite force on the bat. Both the bat and the ball receive an impulse. The momentum lost by the bat is transferred to the ball. So the bat slows down, the ball speeds up!

2. Elastic Collisions Elastic Collision: two objects before, they hit and bounce off each other. Examples: Bumper cars Hitting a baseball Playing Pool Bowling Air Hockey p i = p f m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f

3. Inelastic Collisions Inelastic Collisions: two objects before, they hit, stick together, and continue to move as one. Examples: Car crash Bullet fired into a block of wood Figure Skating Football Tackle p i = p f m 1 v 1i + m 2 v 2i = (m 1 + m 2 ) v f

4. Explosions Explosions: two objects are stuck together and explode apart, each moving separately afterwards. Examples: Bullet fired from a gun. Throwing a ball Rocket Launch Action/Reaction: Recoil Collisions p i = p f (m 1 + m 2 )v i = m 1 v 1f + m 2 v 2f