1. Forces

3. What is a force? It is a push or pull on an object Force has both size and direction *Contact forces *Noncontact forces

4. Gravity – noncontact force Gravity: attractive force between all objects that have mass. Size of the force depends on masses of the objects and distance between them.

6. Friction – contact force Friction: contact force that resists the sliding motion of two surfaces that are touching. Acts in the opposite direction of motion Air resistance: frictional force between air and moving objects.

7. Combining forces - when more than one force acts on an object, the forces combing and act as one force. - sum of all forces is called the net force. - balanced forces: net force = 0 - unbalanced forces: net force does not = 0

8. Unbalanced Forces and Acceleration - unbalanced force = change in velocity - can change either the speed or direction

9. Balanced Forces and Constant Motion - balanced forces = motion is constant - object either at rest or a constant velocity

10. Newton’s First Law of Motion If the net force acting on an object is zero, the motion of the object does not change. Inertia

11. Newton’s Second Law of Motion The acceleration of an object is equal to the net force exerted on the object divided by the object’s mass

12. Newton’s Third Law of Motion For every action there is an equal and opposite reaction. Forces are the same size and in opposite directions. Force pairs