Question

why earth is round not square

Answer 1

Because of gravity. Gravity is an attraction between masses, and acts in all directions from a given mass. It acts with the same strenght in all directions, too. After a long time of these forces having acted on the masses of the universe (atoms) atoms formed groups of higher density, which have a stronger attraction than single atoms, and eventually enough atoms where close enough together that new atoms were formed…


If the earth was triangular (or 3d version traingula pyramid) or square (cubic) the the points of these shapes would be further away from the centre tha the midpoints of the sides. This means that the points of the shapes would tend to fall/ roll down hill. This process would stop when everything was at eqaul distances from the centre. The shape which has all points equal distances from the centre is a circle so it is circular (a sphere). The same will be true for all alrge bodies with significant gravity. Asteroids can be irregular shapes because their graviational fields are so weak that there is no perceptable force to make things move downhill. If you were on an asteroid, it would be difficult to take a single step without drifting off into space.

Unfortunately ( for the purpose of answering this question), the earth rotates and that makes a difference and so the earth is a bit fatter at the equator than it is at the poles. So the earth is not quite spherical. If you like names - you could call it an oblate spheroid. (Oval or egg shaped to most people)