Newton's Laws of Motion/First Law

Physical Law
Newton's first law of motion is one of three physical laws that forms the basis for classical mechanics.

Statement of Law

 * Every body remains in a state of constant velocity unless it is acted upon by an external unbalanced force.

This of course includes it being stationary, that is, with a constant velocity of zero.

This tendency is sometimes called inertia.

As himself put it:
 * A body remains at rest or, if already in motion, remains in uniform motion with constant speed in a straight line, unless it is acted on by an unbalanced external force.

Also see

 * Newton's Second Law of Motion
 * Newton's Third Law of Motion

It is worth pointing out that Newton's First Law of Motion is in fact a special case of Newton's Second Law of Motion, putting $\mathbf F = 0$.