One student of mine has found one question in a book of thermodynamics (1st year university level).
Work or Heat? You grab a bottle of juice and shake it thoroughly. Is this an example of a work or a heat interaction? Recall that work can be described with mechanical or electromagnetic variables.
My opinion is that we should first define the system. If we take the juice as our system, there is no work done by the system; nor on the system since the system boundaries do not move. There is not heat neither that transverse the system boundary. Am I correct?
On a second thought, I think that we should define the bottle and its content as the system. Then we have clearly a work done on the system.
Is there any contradiction? What am I missing here?