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J. Perelman
"Entertaining physics". Book 1.
Chapter 5. Properties of liquids and gases

DRY OUT OF THE WATER

Put a coin on a large flat dish, pour as much water to cover the coin, and will offer to take her right hand, with dry fingers.

This seemingly impossible task is quite simply solved with the help of glass and burning paper. Light a piece of paper, put it burning inside of the glass, and quickly put the glass on a plate near the coin, bottom up. The paper will turn off, the glass will be filled with white smoke, and then under it by itself will gather all the water from the plate. The coin, of course, will remain in place, and a minute later, when it gets dry, you will be able to take it, don't wet your fingers.

What force drove the water in the glass and maintains it at a certain height? The atmospheric pressure. A burning piece of paper was heated in a glass air pressure him increased, and the gas came out. When the paper is gone, the air is again cooled, but when cooled, its pressure decreased under the glass entered the water, whareama there by the pressure of the ambient air.

Instead of paper, you can use matches, stuck in traffic jam circle, as shown in the figure.


How to collect all the water on the plate under the glass tilted upside down.

Very often we hear and even read an incorrect explanation of this ancient experience. His first description and proper explanation can be found in ancient physics Philo of Byzantium, who lived around the first century BC. Namely, say that it burns up the oxygen and therefore the amount of gas under the glass decreases. This explanation is grossly wrong. The main reason only heated air, and not to absorb part of the oxygen burning paper. This follows, first, from the fact that you can do without burning papers, and just heat the beaker, rinsing it with boiling water. Second, if instead of paper to take cotton wool moistened with alcohol, which burns longer and stronger heats the air, the water rises nearly to one-half Cup; meanwhile, it is known that oxygen is only 1/5 of the total volume of air. Finally you need to keep in mind that instead of “burned-out” oxygen produces carbon dioxide and water vapor; first, however, soluble in water, but steam still occupying part of the place of oxygen.

Entertaining physics J. Perelman

 




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