Concepts of energy

Question:

Our group is having a little difficulty with C-1–Concepts of
Energy. The confusion is that we, the parents, are having
trouble distinguishing the various forms of energy as they are
described–i.e., heat energy, movement energy, etc. There seems to
be a lot of overlap in these concepts–for example, if you rub your
hands together to create heat, is that movement energy creating heat
energy? And if you light a fire, is that heat energy and/or light
energy?

Lauren

Answer:

It is very common to have difficulty regarding energy, so don’t feel you are alone in this.  Yes, via friction movement energy is converted into heat energy.
The concept may be easier to visualize in terms of a spinning wheel. A spinning wheel has a certain amount of movement energy dependent on its size (mass) and its speed of spinning, more technically called momentum. By putting your hand on it to slow it down, there is a conversion, via friction, of that movement energy into heat energy. (Be careful if you try this on a bicycle wheel or such. You can get burned.) Additionally, note the one-to-one, relationship. A larger wheel spinning faster (more momentum) will burn more as you put your hand on it to stop it. If the heat was measure exactly, one could find an exact relationship between heat coming out and the slowing of the wheel (loss of momentum/movement energy).

In rubbing your hands together, you are likewise  converting movement energy to heat energy, but the one-to-one relationship is harder to see because you are continually pumping more movement energy into your hands by way of your muscles, which are running on the potential energy of the food you ate. Importantly, be carful of the word, “created.” You are not creating any energy. You are simply converting the energy from one form to another.

Yes, fire conspicuously emits both heat and light. This is to say that some of the potential energy in the burning material is released as light, some as heat.

Bernie Nebel