Abie L. Benítez
I would like to define and explain some of the terminology that is relevant in teaching about thermodynamics to our students. The first step for me was to understand what thermodynamics means. Of course because of my language background I like to figure out what words mean before I actually look them up. I started by processing through a frequently utilized mental exercise: I was able to discern that it had to do with temperature or heat because of the excerpt of the word “thermo”. Then I thought about dynamics and realize that there was some sort of movement that must be study or observed. This is how I usually process new vocabulary and in my work with my students I try to model this process for them. Now, what thermodynamics does study is the nature of heat and its conversion to or from mechanical, electric and chemical energy. It also is concern with the ability of a system to produce work.
What is energy?
When I think of energy, it is in terms of my desire or capacity to do something. Yet, in physics it is very clear that energy is the ability or capacity to do work or produce change. What do I mean by this? Energy can be measured by studying the interaction that occurs in a system designed to produce work. Forms of energy comprise heat, light, sound, electricity and chemical energy. Therefore, energy is a conserved system property the existence of which is asserted by the first law of thermodynamics (Fenn, 1982). The first law of thermodynamic simply states that for any system there exists a property called energy that is conserved and that can be transferred into or out of a system by either heat or work interactions.
What do you mean by work?
In physics when we talk about work we must make the distinction between work and effort. One may exert effort to do something but in physics terms that effort may not produce work. Then, what is work? It is the capacity that a system has to move a desired object; it is proportional to force and the distance through which is exerted. As with many other physics terms one must be able to mathematically calculate work by placing a value to force and distance and calculating the product of their interaction. Thus, work implies movement as a result of effort. Yet, we could use a tremendous amount of effort by pushing a truck but if we do not move it we have done absolutely zero work.
Heat
Another way of producing change is utilizing heat. What do I mean? One has to take into consideration both the system and its environment. But what is a system? It is a portion of the universe that can be analyzed in terms of thermodynamics. For example, a cloud, an engine or a planet can be considered systems. A system is that which we identify as the object of our attention. Heat is not equal to temperature; heat refers only to energy that is being transferred from one body or mass to another. Thus, heat is what happens between two communicating objects at different temperatures and as the result of the interaction of the system and surroundings that is not work. It is also clear that some objects may act as heat insulators therefore giving us a tool to determine if heat is involved in the interaction. Again, it is in fact the interaction between a hot object and a cold object that are in contact with each other (Fenn, 1982). If we think about objects that are hot such as an iron, the heat from the iron transfers to the cloth making it hot, thus, the heat is transferred to the colder object. The same with a fireplace or a space heater, the heat from the unit transfers into the room air warming it up gradually until it reaches a higher temperature. My understanding is that heat transfers from the hotter object to the colder producing change. According to Fenn (1982) this happens until both objects have achieved the same hotness. Scientist, engineers, and inventors have been able to utilize heat to create the conditions to produce work. The second law of thermodynamics indicates that there has to be a particular direction for all spontaneous processes that produce change, where the flow of heat goes from a higher temperature source and requires the ejection to a lower temperature reservoir. In other words for a system to continue to produce work there must be a sink or reservoir where we can dump some of the heat.
