Newton’s 3rd Law PAGES

Newton’s 3rd law of motion: Forces always occur in pairs For every action force…there is an equal and opposite reaction force Forces in a force pair do not act on the same object Equal forces do not always have equal effects

ACTION FORCE REACTION FORCE Also applies to skateboards… cars…etc… EX 1:

Swimmer pushes backward on wall…wall pushes forward on swimmer Swimmer pushes backward on water…water pushes forward on swimmer EX 2:

Bird flying Given the action force, identify the reaction force: ACTION: REACTION: The wing of the bird pushes the air downward. The air pushes the wing of the bird upward.

Given the action force, identify the reaction force: Firing a rifle ACTION: The hot gas pushes forward on the bullet REACTION: The bullet pushes backwards on the hot gas (which in turn pushes the rifle) The gunpowder explosion creates a hot gas that expands outward

Given the action force, identify the reaction force: Rocket- p 416 ACTION: The rocket pushes hot gases backwards (from the combustion chamber through the nozzle) REACTION: The hot gases push the rocket forward (up)

A. Momentum ___________ is a property of all moving objects For movement along a straight line, momentum is calculated by multiplying an object’s _____ and ________: momentum = mass x velocity p = mv Momentum massvelocity

momentum = mass x velocity p = mv Momentum is expressed in ________ Like velocity, momentum has _______. An object’s momentum and velocity are in the same direction. kg  m/s direction P m v

The greater the mass of an object, the ________ the momentum of the object. Ex. a tractor trailer truck has much more momentum than a sports car moving at the same speed. greater

The faster an object is the ________ the momentum of the object. If an object is not moving its momentum is ______. greater zero

B. Practice Problems 1. Calculate the momentum of a ____ kg speed skater moving forward at ____ m/s p = mv = (75 kg)(16 m/s) = 1,200 kg  m/s forward 75 16

2. Calculate the momentum of a ____ kg ostrich running north at _____ m/s p = mv = (135 kg)(16.2m/s) = 2,190 kg  m/s north

3. Calculate the momentum of a ____ kg passenger seated on a train that is __________ p = mv = (48.5 kg)(0 m/s) = 0 kg  m/s 48.5 stopped

4. Calculate the velocity of a ____ kg kitten with a forward momentum of ____ kg  m/s v = p/m = (5 kg  m/s)/(0.8 kg) = 6m/s forward 0.8 5

C. Conservation of Momentum When a moving object hits a second object, some or all of the momentum of the first object is ___________ to the second object The total momentum of two or more objects after a collision is the _____ as it was before the collision transferred same

Ex. Imagine hitting a billiard ball with a cue ball so that the billiard ball starts moving. During the collision, the cue ball transfers some of its momentum to the billiard ball The cue ball hits the billiard ball with a force – the _______ force. The equal but opposite force exerted by the billiard ball on the cue ball is the ________ force action reaction

Law of Conservation of Momentum Law of conservation of momentum states the total amount of momentum in an isolated system is conserved Anytime two or more objects interact, they may exchange momentum, but the total momentum of the system stays the ______. same