Second Law Of Thermodynamics

[Khandro]

... states that heat travels to cold, never the reverse, but when I open the outside door to an otherwise sealed warm room it appears to me that the cold air from outside is 'coming in'. What exactly is happening ?

[Old_Geezer]

Convection. Masses of air at a cooler temperature can enter to replace the warmer air leaving.

Heat is usually considered when the material it is traveling along isn't itself moving.

[gingejbee]

...the cold air is coming in to take the place of the warm air going out.
This is all about air currents...not about heat energy being transferred by conduction, covered by the laws you mention.

[Sqad]

Your body transmits heat when you open the door to the cold outside.
This lowers you body temperature and thermoreceptors transmits this fall in body temperature to the brain and you feel colder.

[jim360]

The other point I'd like to add is that the Second Law of Thermodynamics (SLT) doesn't quite say that. Depending on the precise formulation, it states more specifically that, "heat can never pass from a colder thing to a warmer thing without something external driving this".

[Khandro]

Thank you, what made me ponder this was someone saying, close the door you're letting all the cold air in (but not quite so politely!) So the cold air rushing in is replacing the warm air rushing out & if the outside & inside temperatures were the same, nothing would happen.

I suppose it's now a bit obvious. Silly me.

[Theland]

Wear your winter knickers!

[Karolina82]

Consider a closed system with two bodies in contact. If body A has a higher temperature than body B then heat energy will flow from A to B.
Are heat and temperature the same thing? I heard a Formula 1 commentator talking about getting "temperature" into the tyres.
Is there a simple definition of temperature?

[gingejbee]

^heat is a form of energy that a body has. Temperature is simply a measurement of how much (or little) heat energy that body has.
(Body, here, meaning any item, inanimate or otherwise).

[Khandro]

Having given it a bit more thought, isn't it more accurate to say that you open the door & the warm air goes out, because that is the prime movement - the cold air coming in is simply a consequence of that ?

[Old_Geezer]

As far as convection is concerned I rate both equally valid as it's air movement responsible not heat transfer. But if you prefer one rather than the other, that's fine.

[Karolina82]

The prime mover would be the cold air. It is denser than warm air therefore gravity would tend to pull the cold air downwards.
Talking of prime movers, why should air bubbles rise in water against the direction of the gravitational field?

[mushroom25]

[bhg481]

Karol //why should air bubbles rise in water against the direction of the gravitational field//
Think of it as the heavier water getting under the bubbles.

[david small]

I sat on a cold metal bench the other day. Believe me I could feel the heat leaving my lower regions at a rate of knots. I think that I could have sang soprano.

[Karolina82]

Or gravity pulls the denser water downwards at the expense of the less dense air. The gravitational potential energy of the system will be reduced if the air bubbles rise.

[Karolina82]

The metal benches, particularly in train stations, are cunningly designed so that the average warm-blooded human must minimise their sitting time. Hypothermia awaits otherwise.

[Karolina82]

Thank you bhg.

[Khandro]

mushroom; That's brilliant, hope jim watches it.
Donald was the father of Stephanie Flanders who seemed to be always on the news talking about economics, I haven't seen or heard of her for some time.

[woofgang]

as a side comment to this there was a gizmo designed to "reflect" cold from a pile of icecubes to keep heat sensitive samples under a microscope cold...of course you can't "reflect" cold.... I did a quick search for anything on this but can't find it....sure I saw it on TV a few months ago

[Atheist]

Heat versus temperature.
https://energyeducation.ca/encyclopedia/Heat_vs_temperature
Incidentally, when you open a door between a hot room and a cold exterior, you could imagine the heavy cold air oozing in at floor level to take the place of the hot air that oozes out at high level. Like a sliding sash window, open the bottom and top sashes a bit and cold air pours in the bottom and hot air flies out the top.