What is fire?

Question: What is fire? This is a common question that comes up in connection with Lesson A-2.

Answer:

What do you experience as you observe fire? You see light and feel heat, do you not? These are forms of energy (see Lesson C-1). Therefore, fire is energy in the forms of heat and light being given off by the burning process. The further question or puzzelment is: Where does this energy come from?

It will be evident that in the burning process (combustion) the fuel is consumed. Whether or not, or to what degree, you get into the chemical reaction of combustion will depend on the age and background of your kids. The basic concept, in any case, is that fire is the release of potential energy stored in the fuel. That potential energy comes out in the kinetic forms of heat and light as the burning proceeds. The energy of the two would add up to the amount stored in the fuel. Do add that the fuel is NOT “turned into energy.” The fundamental particles (atoms) of the fuel remain; they are only rearranged into to gas (carbon dioxide) and water vapor that are given off into the air.

Some may wish to argue that in flame kids are observing plasma. Introduction of plasma at this level is likely to cause more confusion and misunderstanding than clarification. Therefore, I recommend keeping it in terms of what kids actually observe, which is heat and light. There is plenty of time to introduce plasma at more advanced levels (probably high school).