How cooks put their fingers in hot sauce without burning themselves

Heat =/= temperature

Temperature is the average kinetic energy of the particles in a substance.

Heat is energy transferred from one body to another due to a difference in temperature.

Hot things - like boiling water or simmering sauce - conduct energy to cool things - like your finger.

The amount of energy you get from that hot sauce depends on way more than the temperature of the sauce. More mass of sauce that you get on your finger means more molecules with that same average kinetic energy, so more total energy, so more pain.

In this video Adam switches mass out for time in contact with the sauce, but in this case that seems a fair swap.

Don't dunk your finger in hot fryer oil or hot sugar syrup. According to Adam, go ahead and dunk (or flick) your finger in hot, water- or oil-based sauces.

As always, vinegar leg on the right.

XKCD - hand dryers (2743)

Source - XKCD.com/2743/

See, it's funny because I've never thought about that being the reason hand dryers don't seem to put out hot air as quickly as it seems like they should.

It's the same idea as trying to brown a steak. If the outside of the steak is wet, the outside can't brown because the energy is going to evaporate the water which has to happen until all the water is gone, keeping the surface of the meat no hotter than 100 C. Once that water is gone, however, the steak's surface can get hotter and can brown.

Once your hands are dry, they can feel the warmth.

Until then, though, you just get evaporative cooling.

Can you light a match with water?

My first teaching job was at Terre Haute South Vigo High School in Terre Haute, Indiana.

At THS (we pretty much just called it Terre Haute South), one of the other science teachers gave me a coiled copper tube that looks pretty much like what's shown in the video and was used for exactly what it's used for in the video.

I think I set the demonstration up once...maybe twice ever...and had that copper tube in my storage drawers at three separate schools. I can't remember offhand whether I brought it over to the new building. I think I'll check, though.

But, that's not what the video is about. The video shows how water can be heated to vapor which can then be superheated to a high enough temperature to set a match aflame.

The video also goes on to explain why the copper corrodes so thoroughly.

Kind of cool neat.

A better description of entropy

I open my discussion of entropy in AP chemistry by saying that I'm going to offer an incorrect definition of entropy, that it's the same incorrect definition I was taught in high school and that my students will likely be told in college - as I was - that the high school definition isn't correct...that it's a drastic simplification.

I've said this for years, and I've had other people who study chemistry in college confirm that same story having happened to them, too.

I also will admit that I tried to read PF Atkins's The Second Law without much success.

So, let's try to be a little more precise and correct by watching Steve Mould's video up above - it's a video explaining how a Sterling engine works - and try to be better about what entropy really is.