Re: fanning yourself - can it be effective?
- From: Edward Green <spamspamspam3@xxxxxxxxxxx>
- Date: Fri, 4 Apr 2008 06:11:03 -0700 (PDT)
On Apr 1, 8:16 pm, RichD <r_delaney2...@xxxxxxxxx> wrote:
On a hot day, you see people fan themselves to cool off,
with a magazine for instance.
I watched someone doing that yesterday, and said
"That's an illusion, it can't really cool you, that would
be a violation of the 2nd law of thermodynamics.
Actually, you're generating more heat through muscle action."
P.S. I see nobody has really addressed your question. They are mostly
answering the question "can wind cool you off". The answer to this
one of course is yes. The question you are asking is "but is there a
law to the effect that the amount of muscle heat generated in creating
the wind ourselves will exceed the cooling".
The answer to that is no, but maybe not completely obvious.
We could, as far was thermo is concerned, cool ourselves off in an
isothermal body-temperature heat bath by muscular action, because our
body has the stored ability to do work -- much as if we had a large
weight suspended on a pully. Such a weight can run an airconditioner
-- for a while. In our body the suspended weight is in the form of
chemical free energy, but it amounts to the same thing.
Your friend effectively raises the issue that in expending chemical
energy, there is always waste heat -- but (I think you will just have
to take my work on this), there is no application of the second law
which says this waste heat will always overwhelm the airconditioning
effect. That is what your friend is asserting. Ask him to prove it
mathematically by an explicit use of the second law! That should shut
him up and cool you off besides, because of the loss of a hot air
source.
.
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