Question: Why is the world round

Kevin Motherway answered on 10 Nov 2014:

In a word: Gravity. Everything in the universe is attracted to everything else by gravity. The more mass the more gravity, a ping pong ball in your hand exerts a force of gravity on you and you on it. When you get trillions of tons of mass it exerts a huge force (just like the Earth does on you) If you have two rocks or even particles of dust floating in space the will eventually be attracted to each other by gravity and will join up and stick together. If you have a couple of asteroids the will eventually find each other and join up but they’ll stay as two asteroids as the force of gravity pulling the two asteroids together isn’t enough to overcome the strength of rock the asteroid is made of. However when you get a huge amount of material together maybe 1000km in diameter the gravitational forces are so much that the strength of gravity overcomes the strength of the rock and its pulverized down and the force of gravity pulls the material into a sphere. If the sphere is big enough the heat from pressure build up and the sphere starts to melt and when things go liquid the heavy material will fall to the centre and the light stuff rises to the top. So on earth you get a dense Iron-Nickel core and a less dense silicate crust of rocks. But the earth also spins on its axis and it tries to fling the mass out by centrifugal force (just like if you let go on a merry go round you’d be flung off). Because of this the Earth actually bulges by about 21km at the equator. So the Earth is not actually round but is technically an “oblate spheroid”