Newton's Laws of Motion

Three laws that deal with motion were proposed by Sir Isaac Newton. These three laws together provide the foundation for the understanding of motion and the effect of forces acting on an object.

Newton's First Law of Motion
The first law of motion states:

Every object that is at rest tends to stay at rest and every object that is in motion tends to stay in motion unless an external force is applied to it.

An example of this would be a water bottle, which may be right in front of you. If no force is applied to the bottle (no pushing, no pulling, etc), the bottle would stay in that position. However, if you push the bottle, it may turn over and start to roll; and unless a force is applied (such as friction, air resistance...) to stop the bottle, the bottle would keep rolling forever. This law is also known as the Law of Inertia.

Newton's Second Law of Motion
The second law of motion states:

When a net external force is acted on an object, the relationship for the acceleration of the object, the mass of the object, and the net force is inline:F=ma>.

This means that a net external force can change the speed/direction of an object, and that mass times acceleration equals the force applied. For more information about the formula, Click here

Newton's Third Law of Motion
The third law of motion states:

For every action/force, there is an equal and opposite reaction.

This means that if an object 1 exerts a force on object 2, then object 2 also exerts force on object 1 (same equal force). Therefore, there is always a pair of forces acting on the objects in a system.