Answer to Question #3614 in Astronomy | Astrophysics for Anna

Question

Why the Earth is round?

Answer 1

It all comes down to gravity.

One of the effects of mass is that it attracts other mass. For small
objects, like your computer, your car, and even a building, the force of
gravity is tiny. But when you have millions, and even trillions of tonnes of
mass, the effect of the gravity really builds up. All of the mass pulls on
all the other mass, and it tries to create the most efficient shape… a
sphere.

For smaller objects, like asteroids, the force of gravity trying to pull the
object into a sphere isn’t enough to overcome the strength of the rock
keeping it in shape. But once you get above a certain mass and size, the
strength of the object can’t stop the force of gravity from pulling it into
a sphere. Objects larger than about 1,000 km in size are able to pull
themselves into a sphere.



And if you wanna know, actually the Earth is not a proper sphere, it's a
sphere flattened along it's axis of spin.