Newton's law of Universal Gravitation

No one can deny that this is the best part of high school physics.. right?

It had long been believed by astronomers that planets revolve in a perfect circle until Kepler proved that real orbits are elliptical.

From tons of data taken by an Astronomer called Tycho, Kepler found out a relationship between the time taken for planets to complete one orbit and the semimajor axis (radius) of the ellipse.

Period^2  ∝ semimajor axis^3

This is known as Kepler's third law of planetary motion.

Another great physicist, Newton played around with this theory of elliptical orbits and his laws of motion. (F=ma, force is directly proportional to mass)

With some knowledge from the physics of circular motion, he came up with this equation:

This means that everything with mass, from apples and Earth to the Sun and all the planets attract each other. Everything around you is being attracted to you:) The only reason why you don't feel the pull from say, your screen you are reading this from, is because the gravitational constant G is extremely small.

G= 0.000000000066743

So if two masses are very small, this force becomes so tiny that you feel nothing. Therefore Gravity is known as the weakest force there is.

However, when the product of two masses go huge, the force indeed become strong. It is the driving force that sets massive planets in orbit around stars, and massive stars in orbit around the center of galaxies. It is the very force that rules the universe.