Norseman

http://www.varsity.utoronto.ca/archi.../hotcoals.html

Okay, well this isn't news, but there's a fun experiment for all of you to try. If you have a non-teflon cooking pan, put it on your stove and set it to high. If you place water on your pan, at first the water will just simply evaporate within seconds. As the pan gets hotter the water eventually reaches a point where it actually ends up floating just over the pan on a cloud of steam, and since steam is a poor conductor of heat, the water begins to last much longer. Just a few minutes ago I tried this out, and I managed to get some water to do laps around the inside of the pan (due to the near frictionless action, I was able to have it go around dozens and dozens of time) for at least a minute or two without evaporating at well past the temperature that I could have had water evaporating in under 5 seconds. It's one of the more insane things I've ever seen. Try it for yourself.

atheisticprophet

That's very interesting. I might try it out one day.

Origian

I love these random little "effect" thingies - another of my favourites is the Mpemba effect (http://en.wikipedia.org/wiki/Mpemba_effect).

Basically, under some circumstances, hot water will freeze faster than cold water. I remember trying it once, and it did actually work - fascinating. How does it work? Nobody really knows......

Bobinius

Actually I first saw ( and tried it for my self) the Leidenfrost effect in a documentary where a physicist was testing the 'miracle' of walking on burning coals with naked feet.

He used the Leidenfrost effect to help him walk thru the coals. His feet were sweaty and protected him from the direct burn with the aid of the Leidenfrost effect.

Thundun

This effect is one of many reasons why liquid nitrogen is so much fun to play with!

Dark Knight Bob

You can do things like that when you iron your clothes. You can have a lot of fun trying to balance the droplets on the flat surface of the iron and keep them from falling off until they evapourate.

epepke

The Leidenfrost effect is only a minor contributor to walking on coals. There's a group of firewalkers somewhere (New Guinea?) who meticulously dry their feet before walking.

Most of the reason that you can walk on coals is that the ash around the coals is a pretty good insulator. Don't try walking on really fresh coals; I knew someone who was badly burned from this.

perfessor

Um - good advice. Reminds me of the line about skydiving - why jump out of a perfectly good airplane?

I heard about the leidenfrost effect long ago (never knew the name til now). I've used it as an example of "logical" traps.

epepke

In the "don't try this at home, kids" category, when I was a kid and had just learned about the Leidenfrost effect, I dipped my finger into some molten lead with no damage. However, the lead has to be really hot. If it's just molten, some of it might solidify around the finger. This is not fun.

Also in the "don't try this at home, kids" category, there's a thing that one can do in biker bars. Offer a $100 note to the meanest biker if he can hold it taut against his arm and burn a hole through it with a cigarette. It's impossible. The blood in the arm cools it, and the end of a cigarette doesn't have much heat capacity.

perfessor

Here's another one - my former boss said he used to win bets by putting out a cigarette in a bucket of gasoline. The trick involved only doing it when the temperature and humidity were right - I forget the details, and I'm not going to conduct experiments to find out!