Calculate the kinetic energy of rotation of the earth about its axis, and compare it with the kinetic energy of the orbital motion of the earth’s centre of mass about the sun. Assume the earth to be a homogeneous sphere of mass 6.0*10^24kg and radius 6.4*10^6m. The radius of the earth’s orbit is 1.5*10^11m. to get the kinetic energy you will need this formula ke=1/2mv^2 then i have calculated that the total earth's kinetic energy by spinning is 4.8x10^29 joules if we can think of a way to tap the earth's kinetic energy. The Earth's kinetic energy is (mv^2)/2 in its orbit about the sun.