Kepler's Law of planetary motion
There are three Kepler's Law:-
Kepler's 1st law
The orbit of each planet is ellipse with the sun at one focus.
It is based on law of conservation of energy.
Kepler's 2nd law
The orbital radius of a planet sweeps out equal area in equal time interval.
This law is based on law of conservation of angular momentum.
Kepler's 3rd law
Also known as law of periods
The ratio of the square of planet period (T^2) to the cube of semi major axis of it's orbit (a^3) is constant.
[{(T^2)/(a^3)}=Constant]
We can better understand Kepler's Law through this video.
https://youtu.be/mDHPziSaNlU