Law 1.  Each thing, in so far as it is simple and undivided, always remains in the same state, as far as it can, and never changes except as a result of external causes...  Hence we must conclude that what is in motion always, so far as it can, continues to move.   (Principles Part II, art. 37)

Law 2.  Every piece of matter, considered in itself, always tends to continue moving, not in any oblique path but only in a straight line.  (Principles Part II, art. 39)

Law 3.  When a moving body collides with another, if its power of continuing in a straight line is less than the resistance of the other body, it is deflected so that, while the quantity of motion is retained, the direction is altered; but if its power of continuing is greater than the resistance of the other body, it carries that body along with it, and loses a quantity of motion equal to that which it imparts to the other body.  (Principles Part II, art. 40)
 

For an overview of Descartes' physics, click here.
 
 

Law I.  Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it.

Law II.  The change of motion is proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.

Law III.  To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.