1. Anything that changes the motion of an object is considered a force
Forces
Anything that changes the motion of an object is considered a force

2. Balanced vs. Unbalanced

3. Friction and Air Resistance (Forces)
Unbalanced forces that act against motion:
Friction
Air Resistance
Gravity
Static Friction – friction between two stationary objects
Example: person trying to push a piano
Dynamic Friction – friction between one or two objects in motion
Example: Car slowing down when driver takes his foot off the gas because of the surface of the road
Air Resistance – friction between air and the object in motion
Example: A parachute slowing free fall acceleration due to gravity

4. Universal Gravitational Force
The gravitational force that one object has on another is directly proportional to its mass and inversely proportional to the distance between the two objects
Example 1: The force of gravity is stronger on earth than the moon because the earth has more mass than the moon
Example 2: The force of gravity is stronger on the earth’s surface than in orbit because the surface is closer to the center of the earth

5. Newton’s 3 Laws of Motion
First Law: Inertia
objects in motion will maintain their velocity until a force is applied
Example: When a car suddenly stops, the passenger will continue to move unless they are prevented from doing so from a force (wearing a seat belt)
Second Law: Fnet = MA
The net force that an object has is directly proportional to its mass and acceleration
Example: Lighter objects require less force to accelerate than heavier ones (pushing an empty cart vs. a full one)
Third Law: Action/Reaction Forces
Every action force applied to an object has an equal and opposite reaction force
Example  The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards.

6. Free Fall and Weight
Free fall acceleration is the rate of acceleration of all objects regardless of size due to the force of gravity
The acceleration of gravity is 9.81m/s2 for all objects on earth
Objects undergoing free fall on another planet of a different size will have a different free fall acceleration value
Weight of an object is a force and is equal to its mass times free fall acceleration
Weight (Fnet) = mass x 9.81m/s2

7. Momentum Momentum is a quantity of motion
It is equal to the mass of an object times its velocity
A heavier object will have more momentum than a lighter object travelling at the same speed
Momentum of an object changes when a force is applied by another object
The total momentum between the two objects is conserved and transferred from one object to another
Example: In bowling, the momentum of the bowling ball is transferred to the pins
The momentum of the ball decreases when transferred to the pins (motion is slowed) because of the force of the pins on the ball
The momentum of the pins increases when the ball strikes because of the force of the ball on the pins