1. Newton’s Third Law of Motion and Momentum
CH12.3

2. Review Newton’s 2nd Law Newton’s 1st Law – Law of Inertia
An object at rest will remain at rest unless acted upon by an outside force.
Newton’s 2nd Law
Force = mass x acceleration (F=ma)

3. Newton’s Third Law Forces always exist in pairs
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
For every action there is an equal and opposite reaction*

4. Newton’s 3rd Law
EX: If you push on a table (action), the opposite and equal reaction will be the table pushing back on you.
EX: If you rear end a car in front of you the action force would be the force your bumper exerts on the other car. The reaction force would be the force the other cars bumper exerts back on your car. These are equal in size and opposite in direction.

5. Action-Reaction Forces and Motion
EX: A swimmer uses their arms to push against the water and create an action force. The water also exerts its equal and opposite reaction force on the swimmer.
The reason these forces do not cancel is because the action force acts on the water, and the reaction forces acts on the swimmer.
Only when equal and opposite forces act on the same object do they result in a net force of zero.

6. Momentum Momentum is the product of an object’s mass and its velocity.
An object has a large momentum if the product of its mass and velocity is large.
Momentum = Mass x Velocity
SI units are kg-meters per second

7. Conservation of Momentum
The law of conservation of momentum states that if no net force acts on a system, then the total momentum of the system does not change.