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

BUBBLES

Do you know how to blow bubbles? It's not as easy as it seems. And it seemed to me that there is no skill don't need, until I was convinced that the ability to blow big and beautiful bubbles is a kind of art that requires exercise. But is it worth to do such an empty thing, like blowing bubbles?

At the hostel they are evil fame; at least in the conversation we remember them for not particularly flattering similes. Very different looks at the physicist. “Blow air bubble, " wrote the great English scientist Kelvin, and look at it: you can go your whole life with his study still learn from it physics”.

Indeed, a magical play of colors on the surface of the finest soap films give physics the opportunity to measure the length of light waves, and the study of the tension of these gentle films helps to study the laws of forces between particles, those of the adhesion forces, in the absence of which in the world would not exist nothing but the finest dust.

The few experiments that are described below, do not pursue such serious problems. It's just interesting entertainment, which only introduces us to the art of blowing bubbles. English physicist H. Boyce in the book “bubbles” described a long row of various experiences with them. Interested we refer to this excellent book, here we describe only the simplest experiments.

They can be made with simple household solution of soap [Free varieties for this purpose are less suitable], but for those interested we will find pure olive or almond soap, which is most suitable for large and beautiful soap bubbles. A piece of soap carefully bred in clean cold water, until it's quite thick solution. Just better to use pure rain or snow water, and for the lack of them - boiled and cooled water. To bubbles kept long Plateau advises to add to the soap solution 1/3 of glycerol (by volume). With the surface of the solution is removed with a spoon the foam and bubbles, and then immersed in a thin clay pipe, the end of which the inside and outside smeared pre-soap. Achieve great results and using straws, a length of ten centimeters, cross-shaped split at the end.

Blow a bubble: immersing the tube into the solution, holding the tube vertically, so that it formed a liquid film, gently blow into it. As the bladder is filled with this warm air our lungs, which is lighter than the surrounding room air, blown bubble immediately rises.

If it will be possible to immediately blow the bubble 10 centimeters in diameter, then the solution should be used; otherwise, add in the liquid is still soap up until you can blow bubbles with a specified size. But this test is not enough. Blowing bubble, dip your finger in soapy water and try to pierce the bubble; if he will not break, then you can begin experiments; if the bubble did not survive - we need to add a little more soap.

To perform the experiments must slowly, carefully, quietly. Lighting should be bright, otherwise the bubbles will not show their iridescent play.

Here are some interesting experiments with bubbles.

Soap bubble around the flower. In a bowl or on a tray to pour the soap solution so that the bottom of the plate was covered with a layer of 2 to 3 mm; in the middle, put a flower or a bowl and cover with a glass funnel. Then, slowly lifting the funnel, blow her a narrow tube, is formed a bubble, when the bubble reaches a sufficient size, tilt the funnel, as shown in Fig. 66, releasing from under her bladder. Then the flower will be lying under a transparent semi-circular hood of the soap film, perelivajutsa all the colors of the rainbow.


Experience with soap bubbles: bubble on the flower; the bubble around the vase.

Instead of a flower, you can take the statuette, crowning her head a soap bubble. For this it is necessary to drip on the head of the little figurines solution, and then, when the big bubble is already blown, pierce it and blow out the inside peg small.

A few bubbles in each other. From the funnel used for the described experience, blown, as in the case of a large soap bubble. Then completely submerge the straw in a soap solution so that only the tip of her that will have to take by mouth remained dry, and push it gently through the wall of the first bubble to the center, slowly pulling then the straw back, not pushing her, but to edge out the second bubble enclosed in the first, there is the third, fourth, etc.


Experience with soap bubbles: the number of bubbles in each other; the bubble on the statuette inside another bubble.

The cylinder of the soap film is obtained between the two wire rings. For this purpose, the lower ring lower ordinary spherical bubble, then top to bubble put moistened the second ring and, lifting him up, stretch the bladder until it becomes cylindrical. Interestingly, if you lift the top ring to a height greater than the circumference of the ring, the cylinder in one half of the narrows, the other will expand and then split into two blobs.


How to get soap shape of a cylinder.

The film of a soap bubble is always in tension and presses on a prisoner in her air; directing the funnel to the flame of a candle, you can see that the strength of very thin films is not so insignificant; the flame will significantly deviate to the side.


The air is displaced by the bubble walls.

It is interesting to observe the bubble, when he from the room gets warm in the cold: he apparently decreases in volume, and Vice versa, swells, coming from a cold room into a warm one. The reason is, of course, in the compression and expansion of air contained inside the bladder. If, for example, in the freezing cold at - 15°C bubble volume to 1000 CC, and he with frost came into the room, where the temperature is +15°C, it should increase in volume of about 1000 * 30 * 1/273 = about 110 cubic cm

It should be noted also, that the common understanding of the fragility of bubbles is not quite correct: with proper treatment can save a soap bubble in the continuation of the entire decades. English physicist Dewar (famous for his work on the liquefaction of air) kept bubbles in special bottles, well protected from dust, drying and hot air; under such conditions, he was able to save some bubbles a month or more. Lawrence in America had managed for years to keep bubbles under a glass cover.

Entertaining physics J. Perelman

 




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