For every corresponding pair of cross sections, the area of the cross section of a sphere with radius r is equal to the area of the cross section of a cylinder with radius r and height 2r minus the volume of two cones, each with a radius and height of r. A cross section of the sphere is a circle, and a cross section of the cylinder minus the cones, taken parallel to the base of cylinder, is an annulus. The volume of the cylinder with radius r and height 2r is
, and the volume of each cone with radius r and height r is
. So the volume of the cylinder minus the two cones is
. Therefore, the volume of the sphere is
by Cavalieri's principle.
In Mathematics and Euclidean Geometry, the volume of a sphere can be calculated by using the following mathematical equation (formula):
Volume of a sphere =
Where:
r represents the radius.
Cavalieri's principle states that two geometric figures would have the same volume when they have the same height and the same cross-sectional area (CSA) at every point along that height.
By Cavalieri's principle, a sphere and a cylinder with two cones removed have equal volumes. The volume of the cylinder with radius r and height 2r is
while the volume of each cone with radius r and height r is
.
Furthermore, the volume of the cylinder with two cones removed is
. Therefore, the volume of the sphere is
.