A cup of boiling water is far hotter than a warm swimming pool yet holds far less heat, which is exactly where temperature and heat part ways. Heat put in then travels from hot to cold by three routes: conduction along a metal bar, convection in a pot of water, and radiation, which crosses even a vacuum. A heat engine lives off that flow, yet its efficiency η can never reach 100%, because some heat must always be dumped into the cold reservoir; put in terms of the second law of thermodynamics, the entropy of an isolated system never decreases on its own.
A cup of boiling water is far hotter than a warm swimming pool yet holds far less heat, which is exactly where temperature and heat part ways. Heat put in then travels from hot to cold by three routes: conduction along a metal bar, convection in a pot of water, and radiation, which crosses even a vacuum. A heat engine lives off that flow, yet its efficiency η can never reach 100%, because some heat must always be dumped into the cold reservoir; put in terms of the second law of thermodynamics, the entropy of an isolated system never decreases on its own.
Related topics in Matter & Atom