Site for children

J. Perelman
"Entertaining physics". Book 2.
Chapter 6. Properties of liquids and gases


The usual form of the fountain, attributed to the ancient mechanics Heron, probably known to my readers, let me Remind you here of his device before proceeding to the description of the latest modifications of this curious device. Herenow fountain (see figure) consists of three vessels: the top open and two spherical b and withhermetically closed. The vessels are connected by three pipes, the location of which is shown in the figure. When and there is little water, the ball b is filled with water, and the balloon with the air, the fountain begins to act: water is poured on the tube and in withforcing out the air in the ball b; under the pressure of the incoming air water b rushes through the pipe up and hit the fountain above the vessel and. When the ball b is empty, the fountain ceases to beat.

Old herenow fountain.

This is the ancient form geronova fountain. In our time one of the school teachers in Italy, encourage ingenuity poor conditions of his physical Cabinet, simplified device geronova fountain and came up with such modifications, that anyone can make with simple tools (see the following figure). Instead of balls he used pharmacy flask; instead of glass or metal tubes took rubber. The upper vessel is not necessary to scrape: you can simply insert the ends of the tubes, as shown in the picture above.

Modern modification geronova fountain. Above is a variant of the device plates.

In this modification of the device much easier to use: when all the water from the banks b will be transferred through the vessel and into the Bank with, you can simply rearrange the banks b and with, and the fountain has been restored; we must not forget, of course, you could put the tip on another tube.

Another convenience modified fountain is that it allows you to arbitrarily change the position of the blood vessel and to study the impact of distance levels of vessels at the height of the jet.

If you want many times to increase the height of the jet, you can achieve this by replacing the bottom flasks described device water by mercury, and the air - water:

Fountain, operating pressure of mercury. Jet beats ten times higher than the difference in levels of mercury.

The effect of the device is clear: mercury, flowing from banks to Bank b, displaces water from it, causing it to beat a fountain. Knowing that mercury is 13.5 times heavier than water, we can calculate at what height should rise when this jet fountain. We denote the difference of the levels, respectively, by h1, h2, h3. Now look under the action of any forces the mercury out of the vessel with flows in b. Mercury in the connecting tube is exposed to the pressure from two sides. Right on her acting pressure difference h2 of the mercury columns (which is equivalent to a pressure of 13.5 times higher water column, 13,5 h2) plus the pressure of the water column h1. On the left presses the water column h3. In total mercury fond of power

13,5h2 + h1 - h3.

But h3 - h1 = h2; remanufactured therefore, h1 - h3 on the minus h2 and receive:

13,5h2 - h2 i.e. 12,5h2.

So, mercury enters the vessel b under the pressure of the weight of the water column height of 12.5 h2. Theoretically, the fountain must be so to a height equal to the difference between the mercury levels in the flasks, multiplied by 12.5. Friction slightly lowers this theoretical height.

However, the described device provides a convenient opportunity to get the batter to the top jet. To make, for example, a fountain to beat at a height of 10 m, it is enough to lift one Bank over another by about one meter. Interestingly, as can be seen from our calculations, the rise of the plates and over the bottle with mercury does not affect the height of the jet.

Entertaining physics J. Perelman


System Orphus


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