I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Ex: You roll a ball. It slows down by friction.
II. Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
Ex: You cannot kick a brick wall down, but you can kick a soccer ball because the brick wall is more massive.
III. For every action there is an equal and opposite re-action.
Ex:when a rocket lifts off, the rocket's action is to push down on the ground with the force of its engines, and the reaction is that the ground pushes the rocket upwards with an equal force.