This is a purely conceptual question that I’m having trouble understanding. From what I understand, anytime an energy transfer takes place as work, you can say that something has done work on something else. For example, if the gas in a cylinder with a piston on it pushes back the atmosphere and we take the inside of the cylinder to be the system, we can say the system has done work on the surroundings. My question is: what is the gravitational force doing work ON as it pulls a raised weight initially at rest to the surface of the earth? It clearly can’t be on the weight since the total energy of the system remains the same throughout the process. (By that I mean, although the energy is interconverted within the weight from potential to kinetic energy, no energy is added to the system.) What then is gravitational force doing work on? Thanks in advance!