Ball and its parts

A ball in three dimensions is the set of all points whose distance from a fixed point (the center) is less than or equal to a given number (the radius). The surface of the ball is called the sphere. Parts of a ball include the center, radius, diameter, and the sphere (surface).

Important properties

• The ball includes all points inside and on the sphere.

• The center is a fixed point inside the ball.

• The radius is the distance from the center to any point on the sphere.

• The diameter is twice the radius.

• The volume of a ball of radius $r$ is $\frac{4}{3}\pi r^3$.

• The surface area of the sphere is $4\pi r^2$.