1. kepler's 1st law: law of ellipses
2. kepler's 2nd law: law of equal areas
3. kepler's 3rd law: harmonic law
4. newton's 1st law of motion
5. newton's 2nd law of motion
6. newton's 3rd law of motion
7. newton's law of universal gravitation

the greater the mass, the stronger the gravitational force. the greater the distance, the weaker the weaker the gravitational force.
orbit of planets is not circular but elliptical.
objects resist movement, and moving objects resist stopping.
every action, there is an equal and opposite reaction.
closer to the sun orbit it in a shorter time period than planets further from the sun.
imaginary line joining a planet to the sun sweeps out equal areas in equal amounts of time.
of an object depends on its mass and applied force.