# Thermal energy vs Heat

1. Jan 3, 2012

### bsmm11

According to my text book...

Thermal energy is the kinetic energy of the component particles of an object and is measured in joules.
Heat is the thermal energy that is absorbed, given up or transferred from one object to another.

But later on the book there is a small chapter called THERMAL ENERGY (HEAT) and it says...
"Students should understand that the term thermal energy refers to the non-mechanical transfer of energy between a system and its surroundings." ⓒ IBO 2007

I thought heat is the transfer of thermal energy but all of sudden it says thermal energy is also a transfer of energy. So what is the difference between thermal energy and heat then?

2. Jan 3, 2012

### Staff: Mentor

I think it's saying that thermal energy is transferred by non-mechanical means, not that thermal energy IS energy transfer. Not sure though.

3. Jan 3, 2012

### Naty1

not an easy subject....will take more than one minute to grasp so be patient....I still find it confusing at times...

Good explanations here:
http://en.wikipedia.org/wiki/Thermal_energy#Distinction_of_thermal_energy_and_heat

is explained above...like

maybe also read 'heat' in wiki...and keep in mind they may have been written by different authors.... especially: Semantic Misconceptions

http://en.wikipedia.org/wiki/Heat#Semantic_misconceptions

4. Jan 3, 2012

### my_wan

Yet even the wiki article itself made some absolutist claims with:
http://en.wikipedia.org/wiki/Thermal_energy#Distinction_of_thermal_energy_and_heat
Constraints were first put on the statements in red with Einstein's paper, and subsequent measurements, on Brownian motion. For modern versions involving macroscopic scales of space and time see "Wang et al. Phys Rev Lett, 89, 050601(2002)" and "Carberry et al., Phys Rev Lett, 92, 140601(2004)". For press rease versions of these references in Nature and NewScientist see:
http://www.nature.com/news/1998/020722/full/news020722-2.html
http://www.newscientist.com/article/dn2572-second-law-of-thermodynamics-broken.html

By separating "thermal energy" from "heat" the wiki article actually implies the same extensive property for kinetic energy it denies for 'heat' in defining it an intensive property. Yet since when is kinetic energy an extensive property? If two rocks in space has a kinetic energy ke with respect to each other where is this kinetic energy located? If you try to draw a box around these rocks which frame, even if picking a purely Galilean frame, do you associate the box with? They do not even always have the same combined ke under differing Galilean frames that can be chosen. Even if you choose a box frame that minimizes ke it almost certainly not be minimized after a particle reflection on the box sides. We can call this ke a potential energy in terms of the box as a whole, but in terms of the motions of the particles, treated as separate systems, the potential energy of the system is the kinetic energy of its parts, even if those parts also involve frame dependent carriers other than the idealized particles.

In fact what an extensive property depends on for validity is a mean field limit which is itself a frame dependent construct. If this box is allowed to thermally fluctuate then even the frame that defines it is not constant such that the boxes position must be given a mean value fully justified by Newton's 3rd law, rather than the second law.

The second law appears to be nothing more than a very useful inversion of causality, where the inversion results from assuming the second law is itself the fundamental cause. Its usefulness results from the fact that we can use this causal expectation to predict behaviors in which we do not or cannot know the causal subsystems the system consist of. This gets us into trouble when we start trying to attach this inverted causality to an investigation of the subsystems themselves. The second law is not the cause of itself.

5. Jan 4, 2012

### Naty1

my wan....this verall subject is definitely "above my paygrade"...and although I did not understand all your points, it's an intersting post...and subject....

probably when starting it's best to keep to first semester physics and
thermodynamic texts...I may have been better off then!!!!

Another issue regarding frames of reference and heat: If two observers pass locally, one one accelerating and one inertial, the acelerating observer measures a higher temperature
than the inertial observer as the former has a horizon....this is the Unruh effect...so "counting particles" and making temperature observations is not so simple as once thought.