Re: [Phys-L] heat content

[Bernard Cleyet <bernard@cleyet.org>]

On 2014, Feb 12, , at 12:37, Bill Nettles <bnettles@uu.edu> wrote:

> It would probably do us all much good to go (re)read what Francis Sears has written in his text, An Introduction to Thermodynamics and .....I have the 1953 edition. Chapter 4, The First Law of Thermodynamics has some fairly strong statements about heat, work, and energy and the use of those terms.  A few quotes (you should go read the whole chapter yourself):


My book from 1956/57 class:   [copyright 1950  SECOND EDITION Sixth printing — August 1956]

19.7 INTERNAL ENERGY.  A body may be warmed either by placing it in contact with a second body at a higher temperature, or by doing mechanical work on the body.  For example, the air in a bicycle pump becomes hotter when the piston is pushed down, although it could also be heated by placing it in a furnace.

If ones were given a sample of hot air, it would be impossible to tell by any tests whether it had been heated by compression of by heat flow from a hotter body.  This raises the question as to whether one is justified in speaking of the “heat in a body”, since the present state of the body may have been brought about either by adding heat to it of by doing work on it.  We shall show in Chap. 22 that the proper term to use is “internal energy”, and that the expression “heat energy of a body” is meaningless.  

  From the atomic point of view, the internal energy of a body is the sum total of the kinetic and potential energies of its atoms, apart from any kinetic or potential energy of the body as a whole.  Not enough is known at present about the atomic structure of matter to be able to express internal energies wholly in terms of an atomic model, but we shall show in Cha. 25 in connection with the atomic model of a gas, how internal energy of a gas at low pressure may  be identified with the aggregate kinetic energy of its atoms.  

Even though the details of the atomic picture of matter are not fully understood, we do have definite evidence that atomic energies and velocities, whether in a solid, liquid, or gas, increase with increasing temperature.  Such statements as “the heat in a body is the energy of motion of its atoms” should, however, be avoided.  


The complete section



On 2014, Feb 12, , at 12:37, Bill Nettles <bnettles@uu.edu> wrote:

> NASA words (heat content) are bad. But thermal energy content is bad, too.  Maybe they should say the internal energy of the oceans is increasing primarily due to heat flowing into it from the (warming) atmosphere. 



IIRC, a few years ago (phys-l) there was an effort to "dust bin" the noun heat.

bc  wonders if a material’s temperature may be increased by adiabatic magnetization.