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J. Perelman
"Entertaining physics". Book 1.
Chapter 6. Thermal phenomena

PAPER POT

Take a look at Fig. 1: the egg is cooked in water, poured into a paper hat!


Fig. 1. The egg is cooked in a paper pot.

“But the paper will now light up and the water will fill the lamp”, you say. Try to make the experience, taking for thick parchment paper and securely attaching it to the wire. You make sure that the paper does not suffer from the fire. The reason is that water can be heated in an open vessel only up to the boiling temperature, i.e. up to 100°; therefore, the heated water with the same large heat capacity, absorbing excess heat paper does not allow it to be heated significantly above 100°, i.e., so that it could ignite. (It is more practical to use a small paper box in the form shown in Fig. 2.) The paper does not light up, even if the flames licking at her.


Fig. 2. Paper box for boiling water.

To the same genus phenomena applies sad experience, which inadvertently scattered people do that put the samovar without water: samovar raspivaetsya. The reason is clear: the relatively low-melting solder, and only the close vicinity of water rescues him from a dangerous temperature rise. Cannot be heat sealed pots without water. In the old Maxim machine guns warming of the water prevented the weapon from melting.

You can, next, melt, for example, a lead seal in the box, made of playing cards. It is only necessary to expose the flame is the place of paper that is in direct contact with lead: metal as a relatively good conductor of heat, quickly takes away from paper heat, not allowing it to be heated considerably above the melting temperature, i.e., 335° (lead); this temperature is insufficient to ignite the paper.

Good also the following experiment (Fig. 3): a thick nail or iron (even better copper) rod wrap tightly narrow paper strip, like a screw. Then make the rod with a paper strip into the flames. The fire will lick the paper, scoptic it, but will not burn until the rod is not hot. The clue is in good heat conductivity of the metal; glass wand similar experience would not have been. Fig. 4 depicts a similar experience with a “safe” thread, tightly wound with a key.


Fig. 3. Fireproof paper.


Fig. 4. Fireproof thread.

Entertaining physics J. Perelman

 




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