Comments on: Gene Firewalker

By: slanted tom

slanted tom — Mon, 01 May 2006 14:31:58 +0000

Here’s a different kind hot coal that perhaps someone will care to walk across.

http://www.realityphysics.com/

I think someone will make it. If not here, where?

By: Jeff Nuttall

Jeff Nuttall — Sat, 29 Apr 2006 20:37:35 +0000

Regarding the steak issue: There are other factors to consider too. The steak takes a lot longer to cook than just a few minutes. No doubt there is some heat being carried to Dr. Bickers’ feet through convection and radiation while he’s taking steps over the coals, etc., but he’s not spending all that long walking over the coals. Hold a steak over coals for just a minute or two and then withdraw it and it’s not going to be much changed. I’d imagine if Dr. Bickers wandered continuously over hot coals for half an hour, he might find the experience significantly more painful.

Also, remember that humans, unlike steaks, are alive, and that their systems are actively adapting to the heat. I read an account once (though I don’t have the book with me now where I read it, so I may be misremembering the details) about a certain (apparently rather brave or foolhardy) early researcher who voluntarily spent time in a room heated to a very high temperature, to test human heat tolerance. He brought with him a dog and a steak. I forget exactly how long they spent in there, or what temperature the room was (as I said, I don’t have the book with me, and on what little I remembered I wasn’t able to find anything online with a Google search), but according to the account I read when they left the room the man and the dog were both uncomfortable, but still alive and healthy–but the steak was cooked!

By: Ponderer of Things

Ponderer of Things — Sat, 29 Apr 2006 20:16:29 +0000

Someone was telling me that sweat on the soles of your feet (if you do NOT dip them in water first) helps too – which is why people who are a little nervous of walking across the coals than those who don’t care.

By: Harv

Harv — Sat, 29 Apr 2006 15:12:27 +0000

There’s a series of videos made by Jerrol (sp?) Walker on physics which my class watched in high school. I remember one of them being on fire walking (and another on pluging a wet hand into molten lead). He was one of the authors of my intro physics textbook in college (Halliday, Resnick, & Walker) and had an appendix which talked about similar things. He explained that firewalking was often done at night where there would be dew on the grass or that you might get nervous and your feet would sweat. He described in the textbook about his experience firewalking while clutching a physics textbook to his chest.

As for liquid nitrogen, at Astronomy Camp (www.astronomycamp.org), the prof who runs it does liquid nitrogen demonstrations, including one where campers can “touch Saturn” (liquid nitrogen being about the same temperature as Saturn). He has them open their hands with fingers apart and pointing downward (and no rings on) and pours a little over their hands. No harm done.

The worst that happened to me with it was a little stayed on my glove while I was filling an instrument dewar at the telescope. I now have a glove with a hole in it.

By: Bob

Bob — Sat, 29 Apr 2006 14:16:33 +0000

I’m assuming that Cynthia is questioning whether the conductivity, rather than the temperature is uniform throughout the coal cat-walk, in which case it is since I take it that only coal is being used. Another question I have for anyone who has tried this or knows about it, does the conductivity of the coal vary at all throughout the duration of it’s burn cycle?

By: Clifford

Clifford — Sat, 29 Apr 2006 13:50:30 +0000

Cynthia. The hot spots are irrelevant. It is all one giant hot spot. The temperature is high everywhere. (Temperature and heat should not be confused, by the way.) Nevertheless, the low conductivity means that it cannot transfer heat to you fast enough. Uniformity is irrelevant too….although I imagine it is pretty univform since it has been burning down for at least two hours….. It’s pretty simple, really. Conductivity. That’s it.

Best,

-cvj

By: Cynthia

Cynthia — Sat, 29 Apr 2006 12:18:17 +0000

Spaceman – you are right. Thanks for pointing out my error. Unless Gene is levitating off the hot coals, he does not appear to be utilizing radiation and convection heat transfer in his firewalking experiment. Nevertheless, does not maintaining uniform temperature of the hot coals play a role in the overall safety of this walking experiment? I image “hot spots” conducting to the feet might hurt a bit.

By: Jeff Nuttall

Jeff Nuttall — Sat, 29 Apr 2006 08:51:44 +0000

Rob Knop – Actually, the one time I did manage to do some (very mild) harm to myself with the liquid nitrogen demonstration, it was to my feet. I was wearing sandals that day, and when I poured the liquid nitrogen over my hands some got into my sandals and underneath my feet, and there was enough prolonged contact that–well, it didn’t do any permanent damage, but I did get some blisters for a while.

And yes, reaching into liquid nitrogen definitely does feel cold. (And yeah, of course you can’t leave your hands in for long. Like I said, I had to be sure to to be quick about it.)

By: Spaceman Spiff

Spaceman Spiff — Sat, 29 Apr 2006 03:01:58 +0000

Cynthia – then you are utilizing radiation and convective energy transfer, rather than conduction. The main energy transfer mode for the “hot coal walker” is conduction.

By: Rob Knop

Rob Knop — Sat, 29 Apr 2006 00:48:45 +0000

I’ve never been bold enough to reach into liquid nitrogen, but I’ve watched other people do it. (In grad school, building a spectrometer, we wanted to make sure some parts would still move after thermal contraciton, so we just filled a cooler and plunked them in.)

I’m a temperature wimp anyway, though. And I’m sure it feels *cold*.

If you leave your hands in too long, it would be bad… but that’s true of icewater, too.

I once did suffer from ln2 — poured on the ground, and I was in my socks. And my socks were a wee bit wet. Suddenly, I had ice socks on my feet. That hurt– that was cold.