Laws Of Motion

Laws of Motion, I: Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.

Laws of Motion, II: The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.

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

-- Sir Isaac Newton (1643 - 1727), English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher"), Philosophiæ Naturalis Principia Mathematica (1687)