<Dd> F = G M m r 2 . (\ displaystyle F = G (\ frac (Mm) (r ^ (2))).) </Dd> <P> The work needed to move the body over a small distance dr against this force is therefore given by </P> <Dl> <Dd> d W = F d r = − G M m r 2 d r, (\ displaystyle dW = Fdr = - G (\ frac (Mm) (r ^ (2))) \, dr,) </Dd> </Dl> <Dd> d W = F d r = − G M m r 2 d r, (\ displaystyle dW = Fdr = - G (\ frac (Mm) (r ^ (2))) \, dr,) </Dd>

Escape velocity at the center of the earth