An Etymological Dictionary of Astronomy and Astrophysics

In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton’s shell theorem states that:

1. The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere.

2. The gravitational field inside the spherical shell is zero, regardless of the location within the shell.

3. Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass.
   For the relativistic generalization of this theorem,
   see → Birkhoff’s theorem.

See also: → Newton; → shell; → theorem.