Why Earth is round?

Why earth is round?
Why earth not shaped like a triangle or a square ?
Did you know?
In the past, people imagining earth in the various forms .
Some people think that the earth was flat, square, round, like the ceiling, up high as a mountain.

Until one day a Greek philosopher who lived 500 years BC, named Pythagoras said that "The earth is round".
Some people did not believe his words. However Pythagoras could not prove that the earth is round.

Then why the earth is round? why the earth is not a triangular or square? Okay, lets check. .

Why Earth is round?:

The answer is: Newton's Law
Newton's law called "The Law of Universal Gravitation". This law stated by Isaac Newton via journal Philosophiae Naturalis Principia Mathematica on July 5, 1687 in the form of the formula

The existence of attractive forces between objects that are in the universe. This power is called "Attractive force of gravity", in which a force of attraction that occurs in all of the particles that have mass.
Many objects in the universe are scattered and floating. They gathered together into large chunks, due to the attractive force of gravity is. Because gravitational force is evenly distributed, spherical chunk.
Just like a rolling snowball, more and more large spherical. Similarly, earth, not triangular or rectangular but round like a ball.

And then ... It is proof that the earth is round of a Newton law. Based on the statement Pythagoras in the past.