Hi all, I m having a little problem with the definition of work: -Mechanical work is a force applied through a distance, defined mathematically as the line integral of a scalar product of force and displacement vectors. Work is a scalar quantity which can be positive or negative. -In thermodynamics, thermodynamic work is the quantity of energy transferred from one system to another. It is a generalization of the concept of mechanical work in mechanics. ----->now my real problem comes when i take free gas expansion as an example:normaly work should be equal to 0 (thats what i read in books) How can that be since we have an expansion DV and obviously a force responsible for that expansion P (pressure). In my book it says that work in tha case of free expansion equals to 0 because it defines work as: -distance * force resisting to the movement. In that case i agree that free gas expansion work equals 0 since there is nothing resisting the expansion, however that third definition is in contradiction with the first one. I am so confused.Please help!!