Hi guys, I understand that g is by definition positive, as in the Gravitational field strength. However, my school's notes has defined g as -(GM)/r^2. I don't understand what's that negative sign for, and in what scenario is the negative sign used? By the way, it also defined g as -(d phi/dr) where phi is the gravitational potential and d is the differentiation sign...in this case, it says F=-Gmm/r^2. Thanks a lot!!