A sphere is a ball-shaped object. Each point on its surface is the same distance away from the center.

The Main Parts of a Sphere

The radius is the distance from the center of a sphere to its surface.
The diameter is the line that goes through the center of the sphere and joins two opposite points on the surface. It is twice the length of the radius.

Who Discovered How To Find the Volume of a Sphere?

Archimedes discovered was the first to prove the volume of a sphere.

A Sphere in a Cylinder

If a sphere is placed in a cylinder, the volume of the sphere is exactly two-thirds the volume of the cylinder.
Can you work out why?