Newton's laws of motion

Let us begin our explanation of how Newton changed our understanding of the Universe by enumerating his Three Laws of Motion.

1-Newton's First Law of Motion:

 Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

This  recognize us the Galileo's concept of inertia, and so this is often known as the "Law of Inertia"

2-Newton's Second Law of Motion:

 The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.

3-Newton’s Third law of motion :

For every action there is an equal and opposite reaction.

This law is exemplified by what happens if we step off a boat onto the bank of a lake: as we move in the direction of the shore, the boat tends to move in the opposite direction (leaving us facedown in the water, if we aren't careful!).