understanding Quotes

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.

Just as the system of the sun, planets and comets is put in motion by the forces of gravity, and its parts persist in their motions, so the smaller systems of bodies also seem to be set in motion by other forces and their particles to be variously moved in relation to each other and, especially, by the electric force.

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.

Hypotheses should be subservient only in explaining the properties of things but not assumed in determining them, unless so far as they may furnish experiments.

The description of right lines and circles, upon which geometry is founded, belongs to mechanics. Geometry does not teach us to draw these lines, but requires them to be drawn.

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.

Are not rays of light very small bodies emitted from shining substances?

The same law takes place in a system, consisting of many bodies, as in one single body, with regard to their persevering in their state of motion or of rest. For the progressive motion, whether of one single body or of a whole system of bodies, is always to be estimated from the motion of the center of gravity.

Resistance is usually ascribed to bodies at rest, and impulse to those in motion, but motion and rest, as commonly conceived, are only relatively distinguished; nor are those bodies always truly at rest, which commonly are taken to be so.

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.