4

Producing heat

The interpretations of the last two Phenomena make use of the notion of producing heat. This is what we say in everyday life. There appear to be many different processes that produce heat. (*) Prominent among them are fires and mechanical friction (i.e., rubbing), but we also know that heat is produced when electricity flows through wires (lighbulbs), when the light of the Sun is absobed by a body, or in many chemical reactions.

Interpretation

Even if this causes us some difficulties initially, we have to learn to accept that heat can be produced. In all the phenomena listed above, the heat that evolves from the processes did not exist before. The is no (or virtually no) heat in a piece of wood we burn, and there is hardly any heat in a wire through which we let electricity flow. As we know, we con continue to produce heat indefinitely as long as we let electricity flow. There is no way that this much heat could have existed in the body beforehand.

It is true that we also speak of "producing electricity," but we assume that electricity (electric charge) cannot be produced or destroyed. There are phenomena that show that electric charge is separated into positive and negative charge when we "produce electricity," and that positive and negative charge neutralize when we "let electricity disappear." No such phenomena exist in thermal processes. The wire does not get colder and colder as we let electricity flow through it and as it emits heat.

Study Phenomenon 11 that demonstrates that our models require us to think of heat as a quantity that can be produced.

(*) Note: The technical term for quantities of heat is entropy. What we call heat, and what is officially called entropy by engineers and physicsist is closely related to what scientisits before 1850 called caloric. When presenting phenomena in terms of standard language, it makes sense to keep using the word heat for what we normally call entropy.