European Journal of Applied Physics ISSN: 2684-4451 DOI: http://dx.doi.org/10.24018/ejphysics.2023.5.2.245 Vol 5 | Issue 2 | April 2023 35 Abstract — There were derived many forms of theories of heat during the past three hundred years. At its origins, thermodynamics was the study of heat and engines and therefore, we should be connected to these roots. In this model we present thermons as carriers of heat from hot bodies to cold bodies. The flow of heat is modelled as the transfer of angular momentum of these thermons in the direction from the higher angular momentum to the lower angular momentum of thermons. The mechanical equivalent of heat J is defined as the ratio of the angular momentum of thermons to the temperature of the surrounding. This model newly defines the quantity of heat – entropy S – as the ratio of the angular momentum of thermons to the temperature of the surrounding. This model can open a new window to the microworld where quantum particles transfer their heat content in one direction. However, this direction can be changed via the work done on these quantum particles and to reverse the flow of the angular momentum from lower angular momentum to higher angular momentum of those quantum particles. It will be shown that these very well-known formulae of S to all scholars might still keep some hidden surprising properties. Keywords — Carnot´s heat engines, Measure of the quantity of heat S, Mechanical equivalent of heat J, Thermon angular momentum, Thermon transfer of heat. I. INTRODUCTION 1 The theoretical and experimental observations of heat processes passed through hands of many great old masters, e.g. [1]-[11]. One of those earlier models of heat was based on the carrier of heat termed as caloric, e.g. [12]-[31]. There is one old topic in physics - entropy – the term entropy was introduced by Clausius in 1865 [5] and since that time the meaning of the entropy was many times discussed and evaluated, e.g. [32]- [41]. Benjamin Thomson, Count Rumford, had observed the frictional heat generated by boring cannon immersed in water and showed that the supply of frictional heat was seemingly inexhaustible [42]. James Joule in 1850 [43] determined the mechanical equivalent of heat during his experiments with the friction of water molecules, mercury molecules, and cast-iron atoms in his famous paddle-wheel apparatus. Based on these experiments the effect of heat was ascribed to the mechanical motion of atoms and the caloric theory disappeared from following theories of heat. Recently, Stávek [44] introduced thermons as possible carriers of heat and proposed several experimental tests for the evaluation of the reality of that model. Can we newly interpret the mechanical equivalent of heat J and the quantity of heat termed as the entropy S? II. THE MECHANICAL EQUIVALENT OF HEAT (MEH) The cornerstone of the mechanical theory of heat is the equivalence principle or the mechanical equivalence of heat where heat and mechanical work are equivalent. The historically very important experiment of Joule with his paddle-wheel apparatus was recently discussed [45] and repeated [46]. The experimental values of MEH measured in the 19 th century were collected by Greenslade [47] and Kipnis [48]. It is very difficult to achieve experimentally more precise value of MEH and therefore in the modern time the value of MEH was defined as J = 4.1860 J/cal. Table I from reference [47] surveys these MEH values measured in the 19 th century. 1 Submitted on February 06, 2023. Published on April 19, 2023. J. Stávek, Independent researcher in Prague, Czechia. (corresponding e-mail: stavek.jiri seznam.cz) @ The Mechanical Equivalent of Heat Interpreted as the Angular Momentum of Thermons Jiří Stávek