For every action force,

there is an equal and opposite reaction force.

·      Action-reaction forces act on different objects and are different from balanced forces

·      Rocket propulsion is an example of Newton’s 3^rd Law

Example: action-reaction forces   Action: gases are thrust downward Reaction: rocket is pushed upward One force is on the gas, the other force is on the rocket.

Example: balanced forces       Upward force: Air resistance Downward force: gravity   Both forces are acting on the parachutist.

Momentum—tells how much force is needed to change an object’s motion (how hard it is to stop)

·      momentum = mass x velocity (p = mv)

·      What has more momentum:

o    A sports car or a semi, going at the same speed?

o    A Civic going at 80 km/h or one going at 40 km/h?

·      Law of Conservation of Momentum—momentum can be transferred between objects when they collide

o    Momentum before collision = Momentum after collision