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guslthe formation of water blobs on hot (>100C) surfaces
To patch my pants for good, I bought an iron-on patch and decided to use a pot (the one I use for making noodles) as an iron. I boiled water on it and pressed it on the patch, and even put a heavy weight on it, but it turned out that ~100C wasn't hot enough: after several tries, none of the glue would melt.
So I heated the pot dry, testing the temperature by seeing how spoonfuls of water react in contact with the hot pot. Close to 100 deg, the water immediately spreads out and boils away, but when it gets hotter, to around perhaps 180 deg, the water no longer spreads out, but instead it forms self-contained blobs which move pretty freely, almost without friction. Since they are barely in contact with the pan (kind of like mercury on normal smooth surfaces), they don't evaporate nearly as quickly as the "sticky water" in contact with lower-temperature surfaces. Why this mysterious property?
You can see the blobs move like crazy: they sustain the kinetic energy that you gave them (spoon throw) pretty well and go around the pot like 20 times before settling. Oh, and they don't really settle: they vibrate (the energy certainly coming the heat) with a frequency inversely proportional to their size, and one blob in fact looked like an amoeba, with a big bubble popping up in the middle every 5s or so. Very cool. You could probably invent a game with it, if it weren't such a hazard.
Another effect of this was that the pot was making crackling noises, probably due to differential expansion of the metals in the alloy.
By the way, the hot pot did work for ironing the patch into the pant. Although it took more work than expected, having to heat it more than once.
I remember seeing this waterblob phenomenon on my stove in London. Somehow I knew that it went up to around 300C.
crystal formation on the hand warmer
This could be an interesting experiment to see how people make scientific theories. For a spoiler, click here or follow the LJ CUT. If you want to play with it and make you own theories beforehand, you have to buy a "hand warmer" or "body warmer".
My first theory:
The bag is filled with a supercooled liquid. Pressing the button creates pressure bubble which solidifies (either high or low pressure will solidify the stuff). The initial crystals start a chain reaction, which is exothermic.
Problem: as the crystal heat up, they get softer. If the crystal were hot because of an exothermic reaction, the first crystals should be the first to get hot and thus soft.
Theorizing Away: Perhaps forming crystals prevent softness
Other experiments:
* when boiling the bodybag, leave a few powder-fine crystals (last stages) vs gross crystals (intermediate) and let them cool.
* slow cooling (leave in the hot pan to cool off) vs normal (leave outside) vs fast cooling (throw on cold water)
The fine crystals were very visible and boiled faster than gross crystals. While there is probably a difference in the specific heat of melting, this may also be because the heat gets transferred more quickly in a supple medium.
Now, howstuffworks says that the substance goes back to the melting point, whereas my "Solidifying is Exothermic" theory specifies no limits on temperature.
But I don't understand their theory. Why is the melting point required for the substance to coexist in both states? It's not in equilibrium anyway...
To patch my pants for good, I bought an iron-on patch and decided to use a pot (the one I use for making noodles) as an iron. I boiled water on it and pressed it on the patch, and even put a heavy weight on it, but it turned out that ~100C wasn't hot enough: after several tries, none of the glue would melt.
So I heated the pot dry, testing the temperature by seeing how spoonfuls of water react in contact with the hot pot. Close to 100 deg, the water immediately spreads out and boils away, but when it gets hotter, to around perhaps 180 deg, the water no longer spreads out, but instead it forms self-contained blobs which move pretty freely, almost without friction. Since they are barely in contact with the pan (kind of like mercury on normal smooth surfaces), they don't evaporate nearly as quickly as the "sticky water" in contact with lower-temperature surfaces. Why this mysterious property?
You can see the blobs move like crazy: they sustain the kinetic energy that you gave them (spoon throw) pretty well and go around the pot like 20 times before settling. Oh, and they don't really settle: they vibrate (the energy certainly coming the heat) with a frequency inversely proportional to their size, and one blob in fact looked like an amoeba, with a big bubble popping up in the middle every 5s or so. Very cool. You could probably invent a game with it, if it weren't such a hazard.
Another effect of this was that the pot was making crackling noises, probably due to differential expansion of the metals in the alloy.
By the way, the hot pot did work for ironing the patch into the pant. Although it took more work than expected, having to heat it more than once.
I remember seeing this waterblob phenomenon on my stove in London. Somehow I knew that it went up to around 300C.
crystal formation on the hand warmer
This could be an interesting experiment to see how people make scientific theories. For a spoiler, click here or follow the LJ CUT. If you want to play with it and make you own theories beforehand, you have to buy a "hand warmer" or "body warmer".
My first theory:
The bag is filled with a supercooled liquid. Pressing the button creates pressure bubble which solidifies (either high or low pressure will solidify the stuff). The initial crystals start a chain reaction, which is exothermic.
Problem: as the crystal heat up, they get softer. If the crystal were hot because of an exothermic reaction, the first crystals should be the first to get hot and thus soft.
Theorizing Away: Perhaps forming crystals prevent softness
Other experiments:
* when boiling the bodybag, leave a few powder-fine crystals (last stages) vs gross crystals (intermediate) and let them cool.
* slow cooling (leave in the hot pan to cool off) vs normal (leave outside) vs fast cooling (throw on cold water)
The fine crystals were very visible and boiled faster than gross crystals. While there is probably a difference in the specific heat of melting, this may also be because the heat gets transferred more quickly in a supple medium.
Now, howstuffworks says that the substance goes back to the melting point, whereas my "Solidifying is Exothermic" theory specifies no limits on temperature.
But I don't understand their theory. Why is the melting point required for the substance to coexist in both states? It's not in equilibrium anyway...