M_dow Another free research topic: has anybody tracked the thermal transfer in metal water bottles as they're being filled with cold water? It feels to my hand like there's a warmer edge right before the cold water line reaches where I'm holding it, but I don't know if that's my senses fooling me or if the temperature does actually change

☕ David Antoine Not a physicist but heat will always go from warm to cold by transferring vibrational energy of the molecules or an atomic structure and its electrons. Actually, heat passes from the bottle (getting cold) to the water (getting warm). And it is gradual, with no heat spike or warmer edge of some sort. It will continue up to equalization, from the air, to the bottle, to the water. That is a simple case and explanation. I guess the subject is much more complicated in details. :)