The Laws of Physics

Newton's first law of motion is: Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change by force impressed.

Newton's first law is also called the law of inertia. It states that if the vector sum of all forces (that is, the net force) acting on an object is zero, then the acceleration of the object is zero and its velocity is constant. Consequently: an object that is at rest will stay at rest until an unbalanced force acts upon it, and an object that is in motion will not change its velocity until an unbalanced force acts upon it.

The first point needs no comment, but the second seems to violate everyday experience. For example, a hockey puck sliding along ice does not move forever; rather, it slows and eventually comes to a stop. According to Newton's first law, the puck comes to a stop because of a net external force applied in the direction opposite to its motion. This net external force is due to a frictional force between the puck and the ice, as well as a frictional force between the puck and the air. If the ice were frictionless and the puck were traveling in a vacuum, the net external force on the puck would be zero and it would travel with constant velocity so long as its path were unobstructed.

Implicit in the discussion of Newton's first law is the concept of an inertial reference frame, which for the purposes of Newtonian mechanics is defined to be a reference frame in which Newton's first law holds true.
Newton placed the law of inertia first to establish frames of reference for which the other laws are applicable. To understand why the laws are restricted to inertial frames, consider a ball at rest inside an airplane on a runway. From the perspective of an observer within the airplane (that is, from the airplane's frame of reference) the ball will appear to move backward as the plane accelerates forward. This motion appears to contradict Newton's second law (F=ma), since, from the point of view of the passengers, there appears to be no force acting on the ball that would cause it to move. However, Newton's first law does not apply: the stationary ball does not remain stationary in the absence of external force. Thus the reference frame of the airplane is not inertial, and Newton's second law does not hold in the form F=ma.

The second law of motion states that the change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed. If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both.

The third law of motion states that to every action there is an equal and opposite reaction, or the forces of two bodies on each other are always equal, and are directed in opposite directions. Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other.

In my mind Newton's laws of motion (especially the last one), and his law of gravity, (what goes up must come down), point toward a universe moving in cycles of big bang, big crunch, big bang, big crunch. For more information read my article: Where did the universe come from.

Source: Wikipedia