# will heat always.....

• Aug 1st 2006, 07:09 PM
Celia
will heat always.....
Will heat always flow from an object having more energy to one having less energy?
• Aug 1st 2006, 08:14 PM
Depthangel1
Quote:

Originally Posted by Celia
Will heat always flow from an object having more energy to one having less energy?

depends on the conductivity of the material your transmiting to
hope that helps
• Aug 1st 2006, 08:18 PM
CaptainBlack
Quote:

Originally Posted by Celia
Will heat always flow from an object having more energy to one having less energy?

No, it will flow (spontaneously - as topsquark points out is needed here to
avoid complications) from an object at higher temperature to one at lower
temperature.

The temperature is a monotonic increasing function (usually) of the average kinetic energy
of the constituent molecules of the objects.

RonL
• Aug 2nd 2006, 05:05 AM
topsquark
Quote:

Originally Posted by Celia
Will heat always flow from an object having more energy to one having less energy?

Actually, no. My Thermodynamics is a little rusty, but the Second Law says that heat will spontaneously flow from an object with higher energy to one having less energy. Not quite the same thing.

The point is that if we are doing work on the system we can make heat flow from a cold object to a hot object. This is more or less the operation of a refrigerator. (Remember by doing work on the system we are increasing the entropy. If the change in entropy due to work is large enough to compensate for the decrease in entropy represented by shifting energy in the "wrong" direction then we can do it.)

-Dan
• Aug 2nd 2006, 05:48 AM
CaptainBlack
Quote:

Originally Posted by topsquark
Actually, no. My Thermodynamics is a little rusty, but the Second Law says that heat will spontaneously flow from an object with higher energy to one having less energy. Not quite the same thing.

Temperature not energy!

RonL
• Aug 2nd 2006, 08:55 AM
ThePerfectHacker
Quote:

Originally Posted by topsquark
Actually, no. My Thermodynamics is a little rusty, but the Second Law says that heat will spontaneously flow from an object with higher energy to one having less energy. Not quite the same thing.

Is the 2nd law the entropy law? Why is it different here?
• Aug 2nd 2006, 10:15 AM
topsquark
Quote:

Originally Posted by CaptainBlack
Temperature not energy!

RonL

:o I meant to write "internal energy" there. Oops!

-Dan
• Aug 2nd 2006, 10:23 AM
topsquark
Quote:

Originally Posted by ThePerfectHacker
Is the 2nd law the entropy law? Why is it different here?

To directly answer your question, the "Law of Entropy" is actually a bit of an amalgam (spelling?) of the First and Second Laws.

To explain my original answer in a bit more detail:

My inspiration here is the Clausius statement (which is equivalent to the Kelvin statement, which is the typical one introduced to students) of the Second Law:

"There exists no thermodynamic transformation whose sole effect is to extract a quantity of heat from a colder reservoir and deliver it to a hotter reservoir."

From here we can introduce the concept of entropy and a restricted statement of the Second law is that the entropy of an isolated system must increase until the system reaches equilibrium. We can still use the concept of entropy in open systems and then we reach the conclusion that heat can be transferred from a cold body to a hot body only when the entropy of the system is sufficiently increased by the process.

(The neat thing is that such a transferrence can happen "spontaneously" if we use Statistical Mechanics. The restriction is that there has to be a nearby massive source of increasing entropy...say, for example, the Sun. It won't happen often, mind you, but it can happen.)

-Dan