Term
Kepler's 1st Law: The Law of Elipses 

Definition
The paths of planets around the sun are ellipses. 


Term
Kepler's 2nd Law: The Law of Areas 

Definition
A planet moves so that it's radius vector sweeps out in equal areas in equal times. 


Term
Kepler's 3rd Law: The Harmonic Law 

Definition
The ratio between the wquare of the time needed by a planet to make a revolution around the sun and the cube of it's average distance from the sun is the same for all planets.
T^2/R^3
R= average radius of planet's orbit
T=period of tha planet and time for a revolution around the sun 


Term

Definition
A force that is always directed toward asome particular piont.
All central forces may produce eliptical paths. 

