I tried to make it accessible to a fairly wide audience.
I had it vetted by a couple of 14-year-olds who have never
taken HS chemistry or physics; they didn't follow every
detail but they got the main points.
It's about 5000 words, with 12 illustrations.
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Here's an interesting exercise: Choose the best completion:
Other things being equal, for an ideal gas, ...
__
|__| (A) ... when the temperature goes up, the volume goes up,
and when the temperature goes down, the volume goes down.
__
|__| (B) ... when the temperature goes up, the volume goes down,
and vice versa.