Heat being transferred from colder object to hotter object

Question

My son was watching a YouTube video on entropy (The Most Misunderstood Concept in Physics). At about 11:30, it said that in theory it is possible to observe, say, "heat" moving from colder objects to hotter objects. In real life we never observe it because it is so improbable, etc.. My son asked, and I couldn't answer: Is this something actually tested and observed?

Answer 1

In the realm of macroscopic systems used for measuring heat flow, the likelihood of heat moving from a colder object to a hotter one is incredibly slim, practically approaching zero. As a result, we rarely observe this phenomenon in our day-to-day lives because its occurrence is highly improbable.

While we don't directly witness heat flowing from colder objects to hotter ones, it's important to note that the theoretical possibility exists. The field of thermodynamics, extensively tested and validated, provides the framework to explain such occurrences.

For a more detailed explanation and additional reading, I recommend checking out the following answer, which offers insights into the concept of heat flow and entropy.

Answer 2

Heat is energy transfer due solely to temperature difference.

The kinetic temperature of an object can be considered a measure of the average translational kinetic energy (KE) of the atoms and molecules of the object.

The average molecular KE is higher for the object with higher temperature. For heat transfer by conduction, KE transfers from the high temperature object to the cold temperature object as a consequence of collisions between the higher energy molecules of the high temperature object and lower energy molecules of the lower temperature object. This results in a reduction of the average KE of the higher temperature object (thus lowering its temperature) and an increase in the average KE of the the lower temperature object (thus increasing its temperature).

However, at the individual molecular level, the KE of individual molecules vary about the average of the collection of molecules. So it is possible for the higher temperature object to have molecules with KE lower than the average to collide with individual molecules in the lower temperature object having KE greater than the average of the lower temperature object, resulting in transferring KE from the lower to the higher temperature object.

However, in order for this to result in an overall transfer of energy from the low to high temperature object (heat from cold to hot) it would be necessary for collisions to selectively occur on average only between the lower KE molecules of the higher temperature object and the higher KE molecules of the lower temperature object, which would be statistically highly improbable since collisions between the molecules should be random.

Hope this helps.

Answer 3

What doesn't happen is a spontaneous flow from a colder to a hotter body, and it is an experimental fact. For example, a cold beer and warm beef on a table tends to evolve to the ambient temperature. The beer doesn't get colder losing heat to the beef, that becomes hotter.

But air conditioners and refrigerators are devices that take heat from a colder environment and delivery it to a hotter one. It is necessary to do work to perform that task however. It is not a spontaneous process.

Answer 4

“Is this something actually tested and observed?“ By it’s very nature, it can’t be experimentally proved. It’s a statistical conclusion which could only be disproved with a repeatable experiment.