Sphere

Sphere, surface produced by the rotation of a circle through 180° about one of its diameters. The intersection of a sphere and any plane is circular; should the plane pass through the center, the intersection is a great circle. The surface area of a sphere is 4 πr², where r is the radius; its volume 4/3πr³. If mutually perpendicular x-, y-, and z- axes are constructed such that they intersect at the center, the sphere's equation is x² + y² + z² =r².