Two identical copper spheres of radius R are in contact with each other. If the gravitational attraction between them is F, find the relation berween F and R.

Explanation

Let M be the mass of each copper sphere and p be the uniform density of copper.
`:' M=(4/3piR^(3))rho`
The force of gravitational attraction between the two sphere is
`F=(GMM)/(R+R)^(2)=G/(4R^(2))(4/3piR^(3)p)^(2)=(4/9Gpi^(2)p^(2))R^(4)`
If `rho` is consistant, then `FpropR^(4).