The unit "calorie" exists whether we like it or not, so I introduce
it as just another energy unit and then have some fun with it. Here
are a couple of problems I've given my students:
The label on a particular candy bar says it contains 480 Calories.
(a) If all that energy could be converted into kinetic energy of a
1000 kg car initially at rest, how fast would the car be moving?
(b) Our classroom holds about 6800 moles of air (molecular mass =
29.0 gm/mole). Suppose the temperature in the room is initially 20 C
and all the candy bar's energy is somehow delivered to the air
molecules. What will the final temperature be, and what will the rms
speed of the molecules be?
(The students are supposed to know that 1 Calorie = 1 kcal = 4186 J.
They always think they've done something wrong when they get the correct
answer to (a)... Question (b) doesn't mean as much to them, but I think
the answer is really fascinating. The Calorie, or food calorie, is
really a LOT of energy!)