Martha Mains, age 11, of South Casco,

Why is the world round?

The world and its sisters, the planets, the stars and the sizable satellites are all more or less sphere‑shaped. This may be because they all spin around. Rotation tends to pull an object into a round shape and the force of gravity tends to pull the heaviest particles towards the center of a rotation ball. So, if the earth started off as a cube, its endless spinning would in time pull down the corners and make it into more or less a sphere.