Re: [Phys-l] Marylin vos Savant again!

["LaMontagne, Bob" <RLAMONT@providence.edu>]

I have had the same experience when I did factory work to pay my way through undergraduate school. Fans often made you feel hotter.

There's not much mystery to this. If evaporation is not involved, a constant supply of air hotter air than your skin constantly passing over it is going to feel hotter than stagnant air that your skin keeps cooler than ambient. Same effect as when a fan blows air that is cooler than your skin - it feels cooler than with no fan.

Bob at PC

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] on behalf of Roger Haar [haar@physics.arizona.edu]
Sent: Tuesday, August 30, 2011 3:59 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] Marylin vos Savant again!

Hi,

        Often during Tucson HOT DRY early summer, I have been
driving in a car and stuck my hand out the window when it
was 105F.  The result was my hand got hotter, yet when
bicycling home, I feel cooled by the air flow.  I suspect
that the explanation of this seeming contradiction is that
when in the car, my sweat glands were on low.  When cycling
they are on overdrive.  (I am dry when I get home but am
soaked after a few minutes in my house with A/C.  I down a
quart of water in the four miles to home.)  I suspect that
sweat glands kick in in response to elevated core temperature.

Thanks
    Roger U of AZ

===============================================================
On 8/30/2011 12:21 PM, John Denker wrote:
> I can't think of any scenario where Marylin's answer makes sense.
>
> a) If the humidity is high, the fan won't help, but then the
>   person won't get dehydrated, contrary to what she said.
>
> b) If the humidity is not high, the fan helps quite a bit,
>   contrary to what she said.  This is why people buy fans.
>   The amount you have to drink to keep hydrated under the
>   stated conditions, sitting on the porch, is not zero but
>   not unreasonable.
>
> *) Maybe there is some other scenario in which what she said
>   makes sense, in which case her answer is only "mostly" wrong
>   ... but I can't think of any such scenario.  More importantly,
>   in any case, she should have /told/ us what she is talking
>   about.  We shouldn't have to guess.
>
> I just got through riding my bike for 30 miles.  It's 105
> in the shade and there's no shade.  Also no breeze.  On the
> other hand, the humidity is 20%, so it's not hard to keep
> cool, given enough to drink.  My point here is that I'm a
> lot cooler when I'm in motion than when I stop.  A fan (or
> a breeze) helps enormously under these conditions.
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