A student investigates the gravitational attraction between two identical small solid spheres kept in a laboratory.
(i) State Newton’s universal law of gravitation.
(ii) The student doubles the mass of each sphere while keeping the separation between their centres unchanged. Explain qualitatively how the magnitude of the gravitational force will be affected.
(iii) Suppose in addition to doubling each mass, the separation between the centres is reduced to one-half of its original value. Calculate the factor by which the magnitude of the gravitational force changes with respect to its initial value.