Meaning of Work

"Work," like heat, is a way energy is transferred from one body to another -- but crucially, work does not require the two interacting bodies to be at different temperatures at all. Rubbing your two hands together makes them hotter purely through mechanical work (friction), even though both hands started at exactly the same temperature; only afterward, when the warmed hands are placed against a cooler chin, does heat additionally flow from the (now-hotter) hands to the chin because of the temperature difference created by the work already done. So in this one everyday example, work raises the hands' temperature, while a subsequent heat flow raises the chin's temperature -- two physically distinct mechanisms. Just like heat, work is a process quantity, transferred either from the s …