why is the world round?

Answer 1

It is partly because of gravitation, which works in all directions at the same time.
An additional reason for not being cube or another weird form can be attributed to surface tension, or surface energy. This is the phenomenon that explains why a drop of water is round.
Basically, having edges or geometrically non uniform surfaces causes increases of energy at these locations.
And to be more precise, our planet is not exactly spherical, it's a little flatter at the poles because of the rotation.

Answer 2

In actuality the earth is not a true sphere as the question (and most textbooks lend to cause belief) but actually is a spheroid with a bulging center.

The Earth and most other solid planets are spheroid (round) in shape for the most part because that shape is the only shape in natural construction that provides the least surface area for the most volume of matter. (Rule of thumb: the smaller the surface area in porportion to the amount of matter contained, the stronger the cohesiveness of said matter)

Another way to test the theory is to take bubble solution and blow air through different shaped bubble wands. Even though the wands are different shapes and sizes, the bubbles will always be spheroid to contain the most air with the least amount of cohesive solution.

The spin of the Earth causes it to bulge a little at the equatorial region, but for the most part its as near as possible to a natural "ball" shape as can be formed.

Answer 3

Because it doesn't want to be square

Addendum: Oh, you want a technical answer? The sphere has the least total gravitational protential of all the shapes of given volume of matter. It's the same reason why water will settle to the bottom of a cup.

Answer 4

ball bearings are not made by grinding till they're round. they're dropped in a vacuum and naturally hardens to a ball. i think that's the nearest answer i can come up with considering the earth is not leaning on anything.