Comments on: The Leidenfrost Effect

The Leidenfrost Effect

GuyZero — Fri, 18 Nov 2005 12:09:20 -0800

The Leidenfrost Effect. It's the reason that water droplets don't instantly evaporate off of a hot plate between 200 and 300 deg C. Another obscure physical phenomenon? Perhaps - except for Jearl Walker, the physicist who uses it for some awesome demonstrations: sticking your hand into molten lead, walking on hot coals and gargling with liquid nitrogen.

By: GuyZero

GuyZero — Fri, 18 Nov 2005 12:09:39 -0800

This essay appeared in my university physics text over 10 years ago and finding it again on the web was real treat.

By: PenDevil

PenDevil — Fri, 18 Nov 2005 12:22:56 -0800

"Fundementals of Physics" By Halliday, Resnick and Walker is still one of the best text books I own. Even though I was a CS major and would never do Physics past first year I refused to sell that book.

By: beagle

beagle — Fri, 18 Nov 2005 12:24:02 -0800

I had a junior high school civics teacher (Mr. Friedlander, Plainfield, NJ) whose personal hero was Kuda Bux, another practicioner of firewalking and various other extraordinary stunts described in detail here.

By: Ogre Lawless

Ogre Lawless — Fri, 18 Nov 2005 12:29:01 -0800

the resulting steam layer insulates the hand How is it that the resulting steam layer doesn't scald one?

By: joecacti

joecacti — Fri, 18 Nov 2005 12:36:07 -0800

I was going to berate you for not calling that first link out as a PDF, but instead I'm going to applaud you for a decent post and thank you for your contribution. Adobe sucks.

By: GuyZero

GuyZero — Fri, 18 Nov 2005 12:37:39 -0800

I believe that steam has a low heat capacity (specific heat? that physics class was along time ago...), so that although it's hot, it doesn't transfer a lot of its heat to your hand. Also, most of these stunts are over in a few seconds, so there's not much heat transferred.

By: ObscureReferenceMan

ObscureReferenceMan — Fri, 18 Nov 2005 12:41:13 -0800

I remember reading somewhere about someone trying do duplicate the "garlge with liquid nitrogen" trick. Only he read it wrong, and thought it was drink liquid nitrogen. Did some severe damage to himself.

By: Aknaton

Aknaton — Fri, 18 Nov 2005 12:53:58 -0800

Gargling isn't the cool (sic) thing to do with LN_2. Rather, put a pool of it in front of your tongue, and blow out across it. Big fog cloud. When running low on breath, spit out the remainder. After four or five times remember to let your lip thaw out. YOU DIDN'T HEAR THIS FROM ME

By: StickyCarpet

StickyCarpet — Fri, 18 Nov 2005 13:04:37 -0800

Make sure you spit, not swallow.

By: FormlessOne

FormlessOne — Fri, 18 Nov 2005 13:07:06 -0800

The Leidenfrost effect is still used today as part of primitive "truth tests." I recently saw a bit of footage on television of some poor woman being forced to lick a hot iron surface three times as a way of determining if she had lied about adultery (the premise being that a nervous person has a dry mouth), and waiting to see if she was burned. I've personally (and accidentally) experienced this by having liquid pewter briefly splashed on a wet hand - no harm, no foul (except for the burns on the worktable.)

By: bonehead

bonehead — Fri, 18 Nov 2005 13:09:09 -0800

I've used this to dip my hand into liquid N₂ during our department's Christmas lecture series. Our darn safety officer woun't let anyone drink the stuff. Funnily enough, they were ok with the guncotton/LO2 demos though....

By: Mr Bluesky

Mr Bluesky — Fri, 18 Nov 2005 13:23:24 -0800

Arggggghhhhhhhhhhhhhhhhhhhhhh!!!!!!!!!!!!! Arggg!! ArgHHHHHHHHHHHHHH!!!!!!!!!!!! $#%$##$###!!!!!!!^%$^%$^%$$%!!!!!! Shit...oh..first you put the hand in water then the led! Stupid directions!

By: Nahum Tate

Nahum Tate — Fri, 18 Nov 2005 13:27:39 -0800

"I must caution that dipping fingers into molten lead presents several serious dangers." You learn something new every day.

By: darkstar

darkstar — Fri, 18 Nov 2005 14:46:46 -0800

RE: Leidenfrost, similar to the LN2 trick, we used to hold a chip of dry ice in our mouths. With a small enough chip, and without letting it localize (i.e., moving it around so it doesn't freeze your teeth or tongue), we could speak somewhat normally with fog effects. Not as dramatic as the LN2 fog effect, but still fun. Disclaimer: this can hurt you if you don't do it right. Duh.

By: russilwvong

russilwvong — Fri, 18 Nov 2005 15:07:25 -0800

Sounds like Walker has gotten some pretty severe injuries himself--scars on his face, major damage to his teeth....

By: alumshubby

alumshubby — Fri, 18 Nov 2005 15:20:18 -0800

In physics class, we had the "bed of nails" thing, and I was the guinea pig; it was no big deal, didn't even hurt. And I did get laid out of it.

By: bardic

bardic — Fri, 18 Nov 2005 15:36:40 -0800

My dad is a retired scientist, and he used to bring home the coolest stuff. My favorite was a chunk of dry ice--hours of fun for the neighborhood kids and myself. Alas, they probably monitor this stuff now. No fun.

By: Phantomx

Phantomx — Fri, 18 Nov 2005 15:56:57 -0800

You can easily get dry ice. They will probably ask what you are getting it for and the simple answer would be for shipping. When we got some for ice cream making it was a dollar per pound. I can't remember what you would search for in the phone book but the places typically cater to large orders.

By: adzm

adzm — Fri, 18 Nov 2005 16:23:54 -0800

I often get dry ice from the grocery store; most of their frozen food and ice cream gets shipped in it. A helpful reminder: although an alcoholic drink with liquid CO2 makes an amazing effect, DON'T do it to a white russian or anything containing milk/dairy. It curdles very, very quick.... ew.

By: MikeKD

MikeKD — Fri, 18 Nov 2005 16:26:40 -0800

Phantomx, I believe some stores offer it. There's a Mollie Stone's by me that I recall having a cooler of dry ice. (on preview, ditto adzm)

By: Aknaton

Aknaton — Fri, 18 Nov 2005 16:43:13 -0800

Some other ways to play, safer than the one I gave above... LN_2: pour some in the chalkwell of a blackboard. It flows sideways along the well, nearly frictionlessly, picking up chalk like water would. After bouncing back and forth a couple of times it boils away leaving little chalk worms. Not as spectacular as the dragon breath, but mildly amusing. CO_2: press the blade of a pair of scissors against a big flat piece. It screams!

By: ltracey

ltracey — Fri, 18 Nov 2005 16:51:11 -0800

I see Dr. Walker all the time at school -- he looks none the worse for wear.

By: blendor

blendor — Fri, 18 Nov 2005 17:03:14 -0800

Adobe sucks. Which is why you should use FoxIt.

By: NewBornHippy

NewBornHippy — Fri, 18 Nov 2005 18:38:20 -0800

I remember my physics professor in high school telling us all the time that water was a chemical wiht tons of interesting properties, some counter intuitive and paradoxal -- I guess other liquids are as interesting, but we've been playing with water for a longer time.

By: bonehead

bonehead — Fri, 18 Nov 2005 19:11:00 -0800

Water is a really weird fluid. For a start it "shouldn't" be fluid at room temperature, most other compounds with it's mass, ammonia, methane, hydrogen fluoride are gases. Gasoline or naptha are much more typical of what most fluids are like.

By: jaronson

jaronson — Fri, 18 Nov 2005 19:46:19 -0800

Hey, I took one of Dr. Walker's courses years ago. It was titled: "Flying Circus of Physics"

By: five fresh fish

five fresh fish — Fri, 18 Nov 2005 19:51:37 -0800

Sounds like a case for Intelligent Atoms, bonehead.

By: Zinger

Zinger — Sat, 19 Nov 2005 06:08:36 -0800

Adobe sucks. For sure it does. Firefox has a fairly decent extension that throws up a dialogue box if you've just clicked a link that's actually a PDF file. Gives you the option of loading the PDF in another tab, reading it as HTML or downloading it. Doesn't always work, and it doesn't solve the problem of the stupid reader and acrotray processes staying resident long after you've closed the browser, but it does prevent your browser from crashing. Cool link, btw.

By: springload

springload — Sat, 19 Nov 2005 14:41:54 -0800

My job is quite liquid N2-intense. I like to toy with it in my hands, but never gargled and don't intend to. We use it to precool cryostats and provide a heat shield to a bath filled with liquid helium. Into the bath goes the real refrigerator, which cools things to 0.03K. When the fridge is pulled out of the helium, you can sometimes see chunks of frozen air attached to it. StickyCarpet's swallow link is quite creepy. The poor student wouldn't just freeze, but also get a major pressure in his stomach. I hope the scars were from surgery, and that he didn't blow a hole in his body...

By: five fresh fish

five fresh fish — Sat, 19 Nov 2005 15:22:15 -0800

I had an otherwise intelligent friend -- he was double-majoring -- take LN2 home because it was so neat. Only he tightened the caps on the thermoses. I don't believe it caused permanent hearing damage; perhaps he had a window rolled down. It did scare the living shit out of him. Dumbass.