Hi, I was deriving an expression for the work done by gravitational force of an object in moving another object from infinity to a distance 'r' from it. I think it should be positive valued because since displacement in this case is in the direction of the gravitational force, so work done by gravity must be positive. But why am I getting a negative valued expression as follows?: Suppose the masses of the two objects A and B are 'M' and 'm'. Then gravitational force between them when located at a distance 'x' is: F=GMm/R^2, suppose B is moved by this force by a small distance dx, then work done by F is: dW= (GMm/R^2)*dx*cos0 (because dx is in the direction of F) = (GMm/R^2)*dx therefore net work done in moving B from infinity to 'r' is: W= integration[(GMm/R^2)*dx] with upper limit r and lower limit infinity, = GMm* [-1/R] from infinity to r = GMm* [-1/r-(-1/infinity)] = GMm* [-1/r+0] = -GMm/r So, why am I getting negative value of work done by gravity even when displacement is in the direction of force?