Newton's Laws of Motion
Isaac Newton (a 17 th century scientist) put forth three laws which explain why objects move (or don't move) as they do and these three laws have become known as Newton's three laws of motion.
1. Every body continues in its state of rest or of uniform motion in a straight line, except in so far as it is compelled by some external force to change that state.
For example -
In a motor vehicle the force of the road on the locked wheels changes the car's state of motion, yet there is no force to change the passengers state of motion. The passengers continue in motion, sliding forward on the seat. A person in motion tends to stay in motion with the same speed and in the same direction ... unless acted upon by the unbalanced force of a seat belt. . The seat belt provides the unbalanced force which brings you from a state of motion to a state of rest. If a seat belt were not used the passengers would continue on until they contacted the decelerating vehicle at the windscreen, steering wheel or dashboard etc.
2. The acceleration of a body is in the direction of, and proportional to, the force that produces it, and is inversely proportional to the mass of the body.
Newton's 2nd Law is easily expressed by an equation:
Acceleration = Force
This is usually shortened to A=F/M or F=MA.
Newton's second law explains how the mass of an object and the amount of force applied to an object are related to acceleration. In brief, it says that the greater the mass of an object, the more it resists being moved and therefore the smaller its acceleration will be. It also says that the greater the force applied to an object, the greater the object's acceleration will be
3. To every force there is an equal and opposite reaction, or the mutual actions of two bodies are equal and opposite.
When you hit another car, you exert a force on that car. That's not the end of it, though. Even if you hit a car that is at rest, that car is also exerting a force on you. These forces are opposite, or moving in different directions from each other.