Dot Physics

Word Police: Use of the word pressure

I know I should just let go, but this is what makes me, me. I understand that there are terms in physics (like for instance ‘pressure’) that are used in all sorts of ways in common language. The problem is when someone tries to explain something scientifically and misuses a word. Pressure means something. It is the average force per area due to collisions of a gas or liquid on a surface. Really, you can see a good animation of this, I have a link and explanation when [I talked about MythBuster’s Lead Balloon](http://scienceblogs.com/dotphysics/2008/09/mythbusters-how-small-could-a-lead-balloon-be/).

So, what is my problem? I was reading this interesting article on [Scientific American.com about solar refrigerators](http://www.sciam.com/article.cfm?id=solar-refrigeration). Here is a small quote:

*The key is the energy exchanged when liquids turn to vapor and vice versa–the process that cools you when you sweat. By far the most common approach, the one used by the refrigerator in your house, uses an electric motor to compress a refrigerant–say, Freon–turning it into liquid. When the pressure created by the compressor is released, the liquid evaporates, absorbing heat and lowering the temperature.*

“Pressure created by the compressor” isn’t too bad (although it might be interpreted by some that pressure is some substance). My biggest problem is the “When the pressure created by the compressor is released” part. How do you release pressure? Yes, you could allow the particles in the gas to stop colliding with the wall and thus “release” them. But aren’t you releasing the particles not the pressure?

I don’t mean to pick on this particular case because it’s not that bad. There are many other cases where the word pressure is used in a really incorrect manner.

On a side note, about the above article, I find cooling to an extremely interesting problem. It is funny how easy it is to heat something up, but so difficult to cool it off.

**PS:** I also don’t like how the article says “absorb heat”. This also implies that heat is a substance. I don’t really like the word “heat”.

Comments

  1. #1 Uncle Al
    October 21, 2008

    compress a refrigerant—say, Freon

    Say what? Chlorofluorocarbons (Freons, CFCs) are remarkably efficient working fluids, non-corrosive, non-toxic, inexpensive, and easy to lubricate with hydrocarbon oils. The Enviro-whiner trinity: Expensive, shoddy, deadly. “Shoddy” was the first recycled wool. How well do you think that worked out?

    Hydrochlorofluorocarbons (HCFCs) – the Enviro-whiner safe and effective Ozone Hole-sparing equivalent – are disasters. They are crappy working fluids, corrosive given traces of moisture (humidity in the air of the refrigeration train before filling), tumorigenic, expensive, and require exotic expensive polyester lubricants also killed by traces of moisture. Or go fluoroether lubes that rescale the whole concept of “expensive”. The International Geophysical Year Ozone Hole of 1957-8 was no different from that in 2008. HCFCs are insanely powerful Greenhouse gases in formerly transparent parts of the atmospheric infrared absorption spectrum. Even a little bit added is disaster, as increasingly observed.

    As HCFCs come out of patent (gee – a financial motive behind jackbooted State compassion?) they are suddenly discovered to be the previous paragraph hence hydrofluorocarbon (HFC) refrigerants. HFCs are the worst working fluids yet enforced. They don’t lubricate. There are no chronic exposure toxicity studies. They are mixed with HCFCs to work at all. If the mixture is not an azeotrope it changes composition by virtual leaks and effusion. HFCs are, of course, remarkably expensive. Do you love Gaia?

    Freedom is being remarkably bad at taking orders from morons. Applied pressure can reverse that equilibrium.

  2. #2 Fran
    October 21, 2008

    I don’t really like the work “heat” either. It is too difficult to use it correctly, and I keep goofing up. Just like the physics textbooks I give my students to read.

    I like to define “heat” as a transfer of thermal energy, but then I keep using it as if heat were a substance. Grr.

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