A box is initially at rest on a frictionless surface. David then pushes it and the box moves across the frictionless surface. Let's discuss this process in the context of thermodynamics, especially the First Law. One way to state it is: ΔU=Q−W (where positive W is work done by the system, negative W is work done on the system.) For the scenario described, let the system be the box. So ΔU refers to the change in internal energy of the box. Question 1: Does ΔU = 0? This should be correct, because U refers to internal energy, which only includes microscopic kinetic and potential energy, and specifically excludes kinetic energy of motion of the system as a whole and the potential energy of the system as a whole. Question 2: What is W in this case? Does the W in the First Law exclude work that affects the system as a whole? This definitely seems to be the case, but I have not been able to find any references on that provide a definition to this effect. Please provide references if available.