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Re: vapor versus gas



At 9:14 AM -0700 7/27/99, paul o johnson wrote:
Leigh

I contend there is a considerable difference between your original statement
"Carbon dioxide is a liquid at room temperature (otherwise CO2 fire
extinguishers wouldn't work)." and your current statement "CO2 fire
extinguishers do indeed contain liquid CO2 at room temperature." Since your
original statement contained no restrictive modifiers, its implied message
was that CO2 is a liquid at room temperature in general, not just in fire
extinguishers.

I totally agree with you that physics teachers should strive for unambiguous
speech. I think you missed the goal in your original statement.

I claim that I did not miss my goal. My goal was to make readers think.

I can't teach passive students. My students have to be engaged learners.
In this case the student's attention is directed to a mundane example
of liquid carbon dioxide at room temperature, the fire extinguisher.
Perhaps he'd never realized that the CO2 was liquid inside. Good, he
learned something.

Most of the carbon dioxide in a room is liquid at room temperature when
the room contains a fire extinguisher, not an uncommon situation. I
suppose that I shouldn't say water is a liquid at room temperature in a
room where there is no liquid water present, most of the water being in
the vapor phase?

Leigh