tags: kitchen science, shivering quarter, streaming video
Before using your quarters for laundry, you should try this little experiment. Push a quarter into a block of dry ice, and you will notice that a strange thing happens. The quarter quivers. Can you explain this phenomenon? [1:18]
What do you predict would happen if you instead laid the quarter flat on the surface of the dry ice? What if you used a penny? how about a spoon?
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The second quarter does not remain upright when inserted, but tilts slightly to one side. The warm quarter causes the dry ice to sublime at a faster rate releasing CO2 gas which occupies a much greater volume than the solid. This expanding gas pushes against the quarter causing it to tilt back toward vertical. Once the gas escapes, gravity causes the quarter to fall back to its original position and the process repeats. If you take something like a hammer and rest the head of it against the dry ice, you can make an awful squealing noise due to a similar effect as the heat moves rapidly up and down.
Another fun trick is to place a chunk of dry ice on a smooth surface. The out-gassing creates a thin cushion of CO2 on which it glides. You can hit it around like an air hockey puck.
Sublimation of the CO2 from solid directly to gas? If you push the quarter in far enough, the quarter cools down to the CO2 temperature and doesn't cause any more sublimation - otherwise it wicks the heat from the air down to the CO2.....
This is my guess.
Predictions for the flat quarter is that nothing will happen. The quarter will reach the CO2 temperature. As for the penny, one would have to know the "heat transmittance" (lol) of the materials that make up the penny.
I'm guessing that the angle of the quarter is significant -- which explains why the trickster did not show the coins edge on, as that would have made it clear that an upright coin doesn't wobble but a tipped coin does.
I thought that the quarter that was shivering quit doing so when it worked its way down a bit. I suspect that the deeply inserted quarters conduct heat only a little way into the dry ice, but a shallowly inserted quarter sublimes CO2 all the way down, so its support is unstable.
I agree that a flat coin will quickly reach dry ice temperature, and won't do anything cool.
A penny would be an interesting thing to try, as the thermal conductivity of copper is so much higher than many other metals.
All of this is just guessing, of course.
This was on Mr. Wizzards World waaaay back when I was a kid. Thinking about 20 maybe 25 years ago.
I guess that when it's slightly inserted, it's off-kilter, leaning on the side of a little groove. There's an air gap on one side of the quarter, and the other side is flush with the dry ice. The CO2 sublimates all over equally (I'm not sure that the quarter has to be particularly warm for this to work, but it would enhance the effect). On one side of the groove, the CO2 can get away to the air, but on the other, the CO2 builds up against the side of the quarter and pushes it over. The process repeats on the other side of the groove. Of course if you really push the quarter in properly, then it doesn't have this unstable positioning so it can't wiggle.