Isaac Newton Force Quotations

I have explained the phenomena of the heavens and of our sea by the force of gravity, but I have not yet assigned a cause to gravity.

The moon gravitates towards the earth and by the force of gravity is continually drawn off from a rectilinear motion and retained in its orbit.

If a projectile were deprived of the force of gravity, it would not be deflected toward the earth but would go off in a straight line into the heavens and do so with uniform motion, provided that the resistance of the air were removed.

The same thing is to be understood of all bodies, revolved in any orbits. They all endeavour to recede from the centres of their orbits, and were it not for the opposition of a contrary force which restrains them to and detains them in their orbits, which I therefore call Centripetal, would fly off in right lines with a uniform motion.

The alternation 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.

A body in motion tends to stay in motion unless acted on by an outside force.

When two forces unite, their efficiency double.