Conservation of Momentum
In the absence of an outside force, the momentum of a system will remain unchanged.
Momentum before = Momentum after
pi = 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!
Elastic Collisions
Elastic Collision: two objects before, they hit and bounce
off each other.
p =p
i
Examples:
• Bumper cars
• Hitting a baseball
• Playing Pool
• Bowling
• Air Hockey
f
m1v1i + m2v2i = m1v1f + m2v2f
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
pi = p f
m1v1i + m2v2i = (m1 + m2) vf
Explosions
Explosions: two objects are stuck together and explode
apart, each moving separately afterwards.
Action/Reaction: Recoil Collisions
Examples:
• Bullet fired from a gun.
• Throwing a ball
• Rocket Launch
pi = pf
(m1 + m2)vi = m1v1f + m2v2f