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 ?

[Khandro]

//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. //

But I feel the cold air immediately on my face (6feet high), & what is "heavy air" please?

[Karolina82]

Hi Khandro, consider two pint glasses A and B. A contains cold air and B contains hot air.
In glass A the air molecules are closer together and in glass B they are further apart.
Therefore the air in glass A is denser than the air in glass B.
Because the volumes of A and B are equal, the air in glass A will be heavier.
I've assumed the air pressure is the same in A and B.

[Peter Pedant]

you need a minus in the equations to show the heat is flowing the other way
and .....

some books say that the calculations are easier - if you look on it as coolth
( negative warmth )

[Peter Pedant]

chrissakes Khandro - read a book on it - a second course of heat is the standard A level text

the second law is delta H = delta G zero minus t delta S

or - in a reversible process - you can get pay back, but in an irreversible process there is always a little bit wasted

and has narfin to do wiv fridges

Carnots text is available on project gutenberg
nichty nochty fridges