[tex]F=G\frac{m_1-m_2}{r^2}[/tex]
[tex]=\frac{(6.67\times10^{-11}N*m/kg^2)(15kg) }{(0.35m)^2}[/tex]
[tex]=1.2\times10^{-7} N[/tex]
Because the weight of one ball is mg = 147 N, the gravitational force between the two balls is [tex]1.2\times10^{-7}N[/tex] or [tex]8.4*10^3[/tex] parts per billion of the weight.
