The First Law can be stated as $\Delta U=Q-W$, where $W$ is the work done by the system. My question is what kind of work $W$ includes. $W$ certainly includes $PV$ work, i.e. expansion and compression of gas. Does it also include work on the system as a whole? For example, if the system is a billiard ball on a frictionless surface, and I push the billiard ball, doing positive work on it, increasing the kinetic energy of the ball. However, both $Q$ and $\Delta U$ are 0, so it seems this kind of work (me pushing the entire system) is not included in $W$. Am I correct? If so, what references spells this out? I was not able to find any references that specify the exclusion of this type of work.
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