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The Leidenfrost Effect
November 18, 2005 12:09 PM   Subscribe

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.
posted by GuyZero (30 comments total)

 
This essay appeared in my university physics text over 10 years ago and finding it again on the web was real treat.
posted by GuyZero at 12:09 PM on November 18, 2005


"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.
posted by PenDevil at 12:22 PM on November 18, 2005


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.
posted by beagle at 12:24 PM on November 18, 2005


the resulting steam layer insulates the hand

How is it that the resulting steam layer doesn't scald one?
posted by Ogre Lawless at 12:29 PM on November 18, 2005


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.
posted by joecacti at 12:36 PM on November 18, 2005


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.
posted by GuyZero at 12:37 PM on November 18, 2005


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.
posted by ObscureReferenceMan at 12:41 PM on November 18, 2005


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
posted by Aknaton at 12:53 PM on November 18, 2005


Make sure you spit, not swallow.
posted by StickyCarpet at 1:04 PM on November 18, 2005


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.)
posted by FormlessOne at 1:07 PM on November 18, 2005


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....
posted by bonehead at 1:09 PM on November 18, 2005


Arggggghhhhhhhhhhhhhhhhhhhhhh!!!!!!!!!!!!! Arggg!! ArgHHHHHHHHHHHHHH!!!!!!!!!!!! $#%$##$###!!!!!!!^%$^%$^%$$%!!!!!!

Shit...oh..first you put the hand in water then the led!

Stupid directions!
posted by Mr Bluesky at 1:23 PM on November 18, 2005


"I must caution that dipping fingers into molten lead presents several serious dangers."

You learn something new every day.
posted by Nahum Tate at 1:27 PM on November 18, 2005


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.
posted by darkstar at 2:46 PM on November 18, 2005


Sounds like Walker has gotten some pretty severe injuries himself--scars on his face, major damage to his teeth....
posted by russilwvong at 3:07 PM on November 18, 2005


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.
posted by alumshubby at 3:20 PM on November 18, 2005


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.
posted by bardic at 3:36 PM on November 18, 2005


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.
posted by Phantomx at 3:56 PM on November 18, 2005


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.
posted by adzm at 4:23 PM on November 18, 2005


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)
posted by MikeKD at 4:26 PM on November 18, 2005


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!
posted by Aknaton at 4:43 PM on November 18, 2005


I see Dr. Walker all the time at school -- he looks none the worse for wear.
posted by ltracey at 4:51 PM on November 18, 2005


Adobe sucks.

Which is why you should use FoxIt.

posted by blendor at 5:03 PM on November 18, 2005


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.
posted by NewBornHippy at 6:38 PM on November 18, 2005


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.
posted by bonehead at 7:11 PM on November 18, 2005


Hey, I took one of Dr. Walker's courses years ago. It was titled: "Flying Circus of Physics"
posted by jaronson at 7:46 PM on November 18, 2005


Sounds like a case for Intelligent Atoms, bonehead.
posted by five fresh fish at 7:51 PM on November 18, 2005


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.
posted by Zinger at 6:08 AM on November 19, 2005


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...
posted by springload at 2:41 PM on November 19, 2005


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.
posted by five fresh fish at 3:22 PM on November 19, 2005


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