give me an equation to find the volume of part of a sphere of x^2+y^2+z^2=R^2 where the volume is between z = hR and z = kR where 0<=h < k <=1

The volume of a sphere is given by the formula V = 4/3 * π * R^3. However, you're looking for the volume of a part of the sphere between two planes z = hR and z = kR.

The volume of a spherical cap (the portion of a sphere cut off by a plane) is given by the formula V_cap = π/6 * h^2 * (3R - h), where h is the height of the cap and R is the radius of the sphere.

In your case, you have two caps: one at z = hR and one at z = kR. The volume of the cap at z = hR is V_h = π/6 * (hR)^2 * (3R - hR) and the volume of the cap at z = kR is V_k = π/6 * (kR)^2 * (3R - kR).

The volume of the sphere between z = hR and z = kR is the difference between these two volumes: V = V_k - V_h.

So, the equation you're looking for is:

V = π/6 * (kR)^2 * (3R - kR) - π/6 * (hR)^2 * (3R - hR)

Simplify this equation to get:

V = π/6 * R^3 * [k^2 * (3 - k) - h^2 * (3 - h)]