Question

Hi~

Why when considering work done in space, there is no positive ? As we know work done is negative as it is nearer to Earth, but when work is done to infinity it increases to from a negative value to zero , so why can't it increase to a positive value?

From a guy in Malaysia~

Answer 1

We can do positive work in a gravitational field. Pick up a book from the floor and you just did.

The question is where do we set zero to be in the gravitational field. We could set to be zero anywhere. By convention we set it to be zero at infinity so that that means the energy level of the gravitational field is everywhere negative. But as I say, that is just a convention of where the zero goes and does mean that gravity can or can not do positive work.