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

PENNY THAT DOESN'T SINK IN WATER

Penny that doesn't sink in water, exists not only in the tale, but in reality. You will see this if you do a few easy experiments. Let's start with the smaller items with needles. It seems impossible to make a steel needle to float on the surface of the water, and yet it is not so hard to do. Put on a water surface shred tissue paper, and on it is completely dry needle. Now just carefully remove the tissue paper from under the needle. Here's how: armed with another needle or pin, lightly dipped the edges of the cloth into the water, gradually approaching the middle; when shred all wet, it will fall to the bottom, the needle will continue to swim.


Needle floating on water.
Top - cut needle (2 mm thickness) and the exact form of recesses on the water (2 times larger).
Below is a way to make a needle float on water with scraps of paper.

Using a magnet, bringing to the walls of the Cup on the water level, you can even control the movement of this floating on the water needles.

If you have the appropriate skills, you can do without tissue paper: capturing the needle with your fingers in the middle, drop it in a horizontal position with a small height on the surface of the water.

Instead of the needle can be made to float pin (both are no thicker than 2 mm), light button, small flat metal objects. Nolavconsole this, try to get a swim and a penny.

The reason for sailing these metal objects that water is poorly wets the metal had been in our hands and therefore are covered with a thin layer of fat. Because around a floating needle on the water surface forms a depression, it can even be seen. The surface of the liquid film, trying to straighten up, pressure up on the needle and the supports it. Supports the needle and the buoyancy force of the liquid, according to the law of navigation: the needle is pushed from below with a force equal to the weight of water it displaced. Just easier to get a swimming needle, if you grease it with oil; such a needle can be directly placed on the surface of the water, and it floats.

Entertaining physics J. Perelman

 




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