Newton's Laws of Motion
Newton's First Law
An object at rest will remain at rest unless acted upon by a force.

An object in motion will remain in motion unless acted upon by a force.
Inertia – the tendency of objects to maintain their current state of motion.
Inertia depends on the mass of an object. The more mass, the more inertia.
Force - A push or a pull
Forces
Balanced forces – Occur when forces are applied to an object equally from opposite directions.
Balanced forces do not cause a change in motion.
Unbalanced forces – Occur when a force on an object is not balanced by an opposite force.
Unbalanced forces produce acceleration (a change in motion).
Acceleration is a change in the motion of an object:
   - Speeding up
   - Slowing down
   - Changing direction
Acceleration is affected by the mass and the force.
Newton's Second Law
The acceleration of an object depends on its mass and the force that is applied.
Greater force causes greater acceleration.
Greater mass results in less acceleration.

 F = ma
  - a is for acceleration
  - F is for force
  - m is for mass
Newton's Third Law
Forces always occur in pairs.
For every force, there is an equal and opposite force.
Example: If a baseball bat exerts a force on the ball, the ball exerts an equal force in the opposite direction on the bat.
Gravity is a force that always produces the same acceleration.
The acceleration of gravity is 9.8 m/s squared.
All objects fall at the same rate in the absence of air resistance.
Weight is the force caused by gravity.
Friction is a force that slows down moving objects. Without friction or other forces, a moving object will continue moving in a straight line forever.