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- Path: sparky!uunet!munnari.oz.au!ariel!ucsvc.ucs.unimelb.edu.au!lugb!news
- From: MATGBB@LURE.LATROBE.EDU.AU (BYRNES,Graham)
- Newsgroups: sci.electronics
- Subject: Re: SHOCKING STORIES
- Message-ID: <1992Aug13.015604.7068@lugb.latrobe.edu.au>
- Date: 13 Aug 92 01:56:04 GMT
- References: <1992Aug2.040705.2697@intacc.uucp> <1992Aug6.101547.5792@etek.chalmers.se>
- <1992Aug9.114705.5110@news.iastate.edu> <1992Aug9.214513.10796@zip.eecs.umich.edu>
- Sender: news@lugb.latrobe.edu.au (USENET News System)
- Organization: La Trobe University
- Lines: 41
- In-Reply-To: stame@emunix.emich.edu's message of 9 Aug 92 21:45:13 GMT
- X-News-Reader: VMS NEWS 1.22
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-
- In <1992Aug9.214513.10796@zip.eecs.umich.edu> stame@emunix.emich.edu writes:
-
- > >Essentially, it works this way: when you have a liquid in contact with ahot
- > >surface (above a certain temperature) the layer of liquid closest to the
- > >surface will vaporize. This vapor-layer is a very poor conductor of heat
- > >so the liquid farther away from the surface doesn't heat up as much.
- > >
- > involved. The feet don't really have time to get hot before the person
- > is across the coals and onto the relatively cool ground once more. If
- > the person's feet are *wet*, however, there's always the chance a small
- > ember will adhere and stay in one place long enough to do some damage.
- > I'll have to go home and root around my books tonight and see if I can
- > dig up the references.
- There are two heat transfer rates important here:
- 1/surface of coals to feet, and;
- 2/body of coal to surface.
- As I understand it (not too well!), its no 2 that makes it possible.
- The idea is that the surface of the coal gives its heat to the foot,
- but heat transfer through the coal is so slow that only a very shallow surface
- layer gives up heat, and so there isn't that much transfered. Since this is
- sci.electronics, think of a huge number of very small caps, each charged up
- with one side to ground. The other terminal of each cap is connected to those
- around it via very large resistors. Then if you touch any terminal, you only
- get the discharge from one small cap, a very small amount from those
- nearby, practically nothing from the ones further back. Even though all
- the caps together might store a huge amount of energy, you only get a very
- small shock.
-
- Apparently the tiles used on the space shuttle have such high thermal
- resistance you can heat em up til they glow, then pick them up bare handed.
- Well burnt coal is very porous, so it is plausible.
-
- Also, with the wet foot argument, remember the difference between heating
- the side of the water away from the skin, and spraying hot steam onto
- dry flesh. The first actually provides evaporative cooling. Try it with
- a hot air hand drier. The air doesn't feel at all hot until your hands
- are dry, does it?
-
- Perhaps the two effects together (+ tough feet) do the trick.
- Graham B
-