- (on behalf of the city of Magdeburg). Two copper hemispheres, empty inside, serve to prove atmospheric pressure in all directions. Dictionary foreign words, included in the Russian language. Chudinov A.N., 1910. MAGDEBURG HEMISPHERES from... ... Dictionary of foreign words of the Russian language
Two metal hemispheres pressed tightly together, which are difficult to separate if the air is pumped out of the space between them. The Magdeburg hemispheres were made in Magdeburg (hence the name) in 1654 by O. Guericke, who, with their help... ... encyclopedic Dictionary
Magdeburg hemispheres- Magdeburgo pusrutuliai statusas T sritis fizika atitikmenys: engl. Magdeburg hemispheres vok. magdeburgische Halbkugeln, f; Magdeburgsche Halbkugeln, f rus. Magdeburg hemispheres, n pranc. hémisphères de Magdebourg, f … Fizikos terminų žodynas
- (physical). Otto von Guericke, M. burgomaster, diplomat and physicist, was the first to seek a means of proving through experiment the existence of empty space [Guericke did not achieve this, but during his lifetime Torricelli showed the existence of emptiness (Torricelli's emptiness)... ...
Two metal pieces pressed tightly against each other. hemispheres that are difficult to separate if the air is pumped out of the space between them. M. p. were made in Magdeburg (hence the name) in 1654 by O. Guericke, who, with their help, clearly demonstrated ... ... Natural science. encyclopedic Dictionary
HEMISPHERE, hemispheres, cf. (book). 1. Half geometric ball, obtained by dividing it by a plane passing through the center (mat.). || An object that has this shape. Hemispheres of the brain (two parts big brain person and... Dictionary Ushakova
Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
- (Pumpen, pompes, pumps) the name of most of the various machines for raising water in pipes, as well as for rarefying and condensing gases. To set in motion a droplet or elastic liquid in an open pipe from one of its cross section… … Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
The article traces the development of chemistry from its very origins, from the times when man learned to produce and maintain fire and smelt metals from ores with its help, then through the era of antiquity and the Middle Ages to our time period... ... Collier's Encyclopedia
Figure 58. Structure of the Mariotte vessel. Water flows uniformly from hole C.
Why is this happening? Mentally observe what happens in the vessel when tap C is opened (Fig. 58). First of all, water is poured out of the glass tube; the level of liquid inside it drops to the end of the tube. With further outflow, the water level in the vessel drops and outside air enters through the glass tube; it seeps through the water in bubbles and collects above it in the upper part of the vessel. Now at all level B the pressure is equal to atmospheric pressure. This means that water flows from tap C only under the pressure of the water layer BC, because the atmospheric pressure from inside and outside the vessel is balanced. And since the thickness of the BC layer remains constant, it is not surprising that the jet always flows with same speed.
Now try to answer the question: how quickly will water flow out if you remove plug B at the level of the end of the tube?
It turns out that it will not flow out at all (of course, if the hole is so small that its width can be neglected; otherwise the water will flow out under the pressure of a thin layer of water, thick as the width of the hole). In fact, here, inside and outside, the pressure is equal to atmospheric pressure, and nothing encourages water to flow out.
And if you were to remove plug A above the lower end of the tube, then not only would water not flow out of the vessel, but outside air would also enter it. Why? For a very simple reason: inside this part of the vessel the air pressure is less than Atmosphere pressure outside.
This vessel with such extraordinary properties was invented by the famous physicist Marriott and was named after the scientist “Mariotte’s vessel.”
Luggage from thin air
In the middle XVII century Residents of the city of Rogensburg and the sovereign princes of Germany, led by the emperor, who had gathered there, witnessed an amazing spectacle: 16 horses tried their best to separate two copper hemispheres attached to each other. What connected them? “Nothing,” - air. And yet, eight horses pulling in one direction and eight horses pulling in the other were unable to separate them. So burgomaster Otto von Guericke showed everyone with his own eyes that air is not “nothing” at all, that it has weight and presses with considerable force on all earthly objects.This experiment was carried out on May 8, 1654 in a very solemn atmosphere. The learned burgomaster managed to interest everyone in his scientific research, despite the fact that this happened in the midst of political turmoil and devastating wars.
Description famous experience with the “Magdeburg hemispheres” is available in physics textbooks. Nevertheless, I am sure that the reader will listen with interest to this story from the lips of Guericke himself, this “German Galileo,” as the remarkable physicist is sometimes called. A voluminous book describing a long series of his experiments was published Latin in Amsterdam in 1672 and, like all books of this era, bore a lengthy title. Here it is:
OTTO von GUERIKE
The so-called new Magdeburg experiments
over AIRLESS SPACE,
originally described by a mathematics professorat the University of Würzburg by CASPAR SCHOTT.
Edition by the author himself,
more detailed and enriched with various
new experiences.
Chapter XXIII of this book is devoted to the experience that interests us. We give its literal translation.
“An experiment proving that air pressure connects the two hemispheres so firmly that they cannot be separated by the efforts of 16 horses.
I ordered two copper hemispheres with a diameter of three-quarters of Magdeburg cubits. But in reality, their diameter was only 67/100, since the craftsmen, as usual, could not produce exactly what was required. Both hemispheres fully responded to each other. A tap was attached to one hemisphere; With this tap you can remove air from inside and prevent air from entering from outside. In addition, 4 rings were attached to the hemispheres, through which ropes tied to the horses' harness were threaded. I also ordered a leather ring to be sewn; it was soaked in a mixture of wax and turpentine; sandwiched between the hemispheres, it did not allow air to pass into them. An air pump tube was inserted into the tap and the air inside the balloon was removed. Then it was discovered with what force both hemispheres were pressed against each other through the leather ring. The pressure of the outside air pressed them so tightly that 16 horses (with a jerk) could not separate them at all or only achieved this with difficulty. When the hemispheres, yielding to the tension of all the horses' strength, separated, a roar was heard, as if from a shot.
But as soon as you turned the tap to open free access to air, it was easy to separate the hemispheres with your hands.”
A simple calculation can explain to us why such a significant force (8 horses on each side) is needed to separate the parts of an empty ball. The air presses with a force of about 1 kg per square cm; The area of a circle with a diameter of 0.67 cubits (37 cm) is 1060 cm2. This means that the atmospheric pressure on each hemisphere must exceed 1000 kg (1 ton). Each eight horses therefore had to pull tons of force to counteract the pressure of the outside air.
It would seem that for eight horses (on each side) this is not a very large load. Do not forget, however, that when moving, for example, a load of 1 ton, horses overcome a force not of 1 ton, but much less, namely, the friction of the wheels on the axle and on the pavement. And this force is - on the highway, for example - only five percent, i.e. with a one-ton load - 50 kg. (Not to mention that when combining the efforts of eight horses, as practice shows, 50% of the traction is lost.) Consequently, a traction of 1 ton corresponds to a cart load of 20 tons with eight horses. This is what the air baggage was that the horses of the Magdeburg burgomaster were supposed to carry! It was as if they had to move a small locomotive, which, moreover, was not placed on the rails.
A strong draft horse has been measured to pull a cart with a force of only 80 kg. Consequently, to break the Magdeburg hemispheres, with uniform traction, 1000/80 = 13 horses on each side would be needed.
The reader will probably be amazed to learn that some of the joints of our skeleton do not fall apart for the same reason as the Magdeburg hemispheres. Our hip joint is just such a Magdeburg hemisphere. You can expose this joint from the muscular and cartilaginous connections, and yet the hip does not fall out: it is pressed by atmospheric pressure, since there is no air in the interarticular space.
New Heron fountains
The usual form of the fountain attributed to the ancient mechanician Heron is probably known to my readers. Let me here recall its structure before proceeding to a description of the latest modifications of this curious device. Heron's fountain (Fig. 60) consists of three vessels: the upper open one a and two spherical ones b and c, hermetically sealed. The vessels are connected by three tubes, the location of which is shown in the figure. When there is some water in a, ball b is filled with water, and ball c is filled with air, the fountain begins to operate: water flows through the tube from a to c. displacing air from there into ball b; under the pressure of the incoming air, water from b rushes up the tube and fountains above vessel a. When the ball b is empty, the fountain stops flowing.
Figure 59. The bones of our hip joints are not disintegrated due to atmospheric pressure, just as the Magdeburg hemispheres are held back.
Figure 60. Ancient Heron fountain.
Figure 61. Modern modification of Heron's fountain. Above is a variant of the plate arrangement.
This is the ancient form of Heron's fountain. Already in our time alone school teacher in Italy, prompted to ingenuity by the meager furnishings of his physics office, he simplified the design of Heron’s fountain and came up with modifications of it that anyone can arrange using the simplest means (Fig. 61). Instead of balls, he used pharmacy bottles; Instead of glass or metal tubes, I took rubber ones. There is no need to make holes in the upper vessel: you can simply insert the ends of the tubes into it, as shown in Fig. 61 above.
In this modification, the device is much more convenient to use: when all the water from jar b has poured through vessel a into jar c, you can simply rearrange jars b and c, and the fountain operates again; Do not forget, of course, to also transfer the tip to another tube.
Another convenience of the modified fountain is that it makes it possible to arbitrarily change the location of the vessels and study how the distance between the levels of the vessels affects the height of the jet.
If you want to increase the height of the jet many times, you can achieve this by replacing water in the lower flasks of the described device with mercury, and air with water (Fig. 62). The operation of the device is clear: mercury, pouring from jar c to jar b, displaces water from it, causing it to flow like a fountain. Knowing that mercury is 13.5 times heavier than water, we can calculate to what height the fountain jet should rise. Let us denote the difference in levels respectively by h1, h2, h3. Now let's figure out under what forces mercury flows from vessel c (Fig. 62) into b. The mercury in the connecting tube is subject to pressure from both sides. On the right it is subject to the pressure of the difference h2 of mercury columns (which is equivalent to the pressure of 13.5 times the higher water column, 13.5 h2) plus the pressure of the water column h1. The water column h3 is pressing on the left. As a result, mercury is carried away by force
13.5h2 + h1 - h3.
But h3 - h1 = h2; Therefore, we replace h1 - h3 with minus h2 and get:
13.5h2 - h2 i.e. 12.5h2.
So, mercury enters vessel b under the pressure of the weight of a water column with a height of 12.5 h2. Theoretically, the fountain should therefore shoot to a height equal to the difference in mercury levels in the bottles, multiplied by 12.5. Friction lowers this theoretical height somewhat.
Nevertheless, the described device provides a convenient opportunity to obtain a jet shooting high upward. To make, for example, a fountain shoot to a height of 10 m, it is enough to raise one can above the other by about one meter. It is curious that, as can be seen from our calculation, the elevation of the plate a above the flasks with mercury does not in the least affect the height of the jet.
Figure 62. Fountain operating under mercury pressure. The jet hits ten times higher than the difference in mercury levels.
Deceptive Vessels
In the old days - in the 17th and XVIII centuries- the nobles amused themselves with the following instructive toy: they made a mug (or jug), in the upper part of which there were large patterned cutouts (Fig. 63). Such a mug, filled with wine, was offered to an ordinary guest, at whom one could laugh with impunity. How to drink from it? You can’t tilt it: the wine will pour out of many through holes, but not a drop will reach your mouth. It will happen like in a fairy tale:
Figure 63. Deceptive jug late XVIII centuries and the secret of its structure.
Honey, drank beer,
Yes, he just wet his mustache.
But who knew the secret of the design of such mugs - the secret that is shown in Fig. 63 on the right - he plugged hole B with his finger, took the spout into his mouth and sucked in the liquid without tilting the vessel: the wine rose through hole E along the channel inside the handle, then along its continuation C inside the upper edge of the mug and reached the spout.
Not so long ago, similar mugs were made by our potters. I happened to see in one house a sample of their work, quite skillfully hiding the secret of the structure of the vessel; There was an inscription on the mug: “Drink, but don’t get wet.”
How much does water weigh in an overturned glass?
“Of course, it doesn’t weigh anything: the water doesn’t hold in such a glass, it spills out,” you say.- What if it doesn’t pour out? - I’ll ask. - What then?
In fact, it is possible to hold water in an overturned glass so that it does not spill out. This case is shown in Fig. 64. An overturned glass goblet, tied by the bottom to one pan of a scale, is filled with water, which does not spill out, since the edges of the glass are immersed in a vessel with water. An exactly the same empty glass is placed on the other pan of the scale.
Which side of the scale will tip?
Figure 64. Which cup will win?
The one to which the overturned glass of water is tied will win. This glass experiences full atmospheric pressure from above, and atmospheric pressure from below, weakened by the weight of the water contained in the glass. To balance the cups, it would be necessary to fill a glass placed on another cup with water.
Under these conditions, therefore, water in an overturned glass weighs the same as in one placed on the bottom.
Why are ships attracted?
In the fall of 1912, the following incident occurred with the ocean-going steamer Olympic, then one of the greatest ships in the world. The Olympic was sailing in the open sea, and almost parallel to it, at a distance of hundreds of meters, another ship, much smaller, the armored cruiser Gauk, was passing at high speed. When both vessels took the position shown in Fig. 65, something unexpected happened: the smaller ship quickly turned out of the way, as if obeying some invisible force, turned its nose to the large steamer and, not obeying the rudder, moved almost directly towards it. There was a collision. The Gauk crashed nose-first into the side of the Olmpik; the blow was so strong that the Gauk made a large hole in the side of the Olympic.
Figure 65. Position of the ships Olympic and Gauk before the collision.
When this strange case was considered in maritime court, the captain of the giant “Olympic” was found guilty, since, the court ruling read, “he did not give any orders to give way to the Gauk going across the road.”
The court, therefore, did not see anything unusual here: the captain’s simple lack of management, nothing more. Meanwhile, a completely unforeseen circumstance took place: the case of mutual attraction of ships at sea.
Such cases occurred more than once, probably before, when two ships were moving in parallel. But until very large ships were built, this phenomenon did not manifest itself with such force. When “floating cities” began to plow the waters of the oceans, the phenomenon of attraction of ships became much more noticeable; commanders of military vessels take it into account when maneuvering.
Numerous accidents of small ships sailing in the vicinity of large passenger and military ships probably occurred for the same reason.
What explains this attraction? Of course, there can be no question of attraction according to the law. universal gravity Newton; we have already seen (in Chapter IV) that this attraction is too insignificant. The reason for the phenomenon is of a completely different kind and is explained by the laws of fluid flow in tubes and channels. It can be proven that if a liquid flows through a channel that has narrowings and expansions, then in narrow parts of the channel it flows faster and puts less pressure on the walls of the channel than in wide places where it flows more calmly and puts more pressure on the walls (the so-called “Bernoulli principle”) ").
The same is true for gases. This phenomenon in the study of gases is called the Clément-Desormes effect (named after the physicists who discovered it) and is often called the “aerostatic paradox”. This phenomenon is said to have been discovered for the first time by accident under the following circumstances. In one of the French mines, a worker was ordered to cover with a shield the opening of an external adit through which compressed air was supplied into the mine. The worker struggled with the stream of air for a long time, but suddenly the shield slammed the adit shut on its own with such force that, if the shield had not been large enough, he would have been pulled into the ventilation hatch along with the frightened worker.
By the way, this feature of the flow of gases explains the action of the spray gun. When we blow (Fig. 67) into elbow a, which ends in a narrowing, the air, moving into the narrowing, reduces its pressure. Thus, air with reduced pressure appears above tube b, and therefore atmospheric pressure drives the liquid from the glass up the tube; At the hole, the liquid enters the stream of blown air and is sprayed into it.
Now we will understand what is the reason for the attraction of ships. When two ships sail parallel to one another, it looks like a water channel between their sides. In an ordinary channel, the walls are motionless, but the water moves; here it’s the other way around: the water is motionless, but the walls are moving. But the effect of the forces does not change at all: in the narrow places of the moving dripping water, the pressure on the walls is weaker than in the space around the steamers. In other words, the sides of steamships facing each other experience less pressure from the water than the outer parts of the ships. What should happen as a result of this? The vessels must move towards each other under the pressure of the external water, and it is natural that the smaller vessel moves more noticeably, while the more massive one remains almost motionless. That is why attraction manifests itself with particular force when big ship quickly passes by the little one.
Figure 66. In narrow parts of the canal, water flows faster and puts less pressure on the walls than in wide parts.
Figure 67. Spray bottle.
Figure 68. Water flow between two sailing ships.
So, the attraction of ships is due to the suction action flowing water. This also explains the danger of rapids for swimmers and the suction effect of whirlpools. It can be calculated that the flow of water in a river at a moderate speed of 1 m per second draws in human body with a force of 30 kg! It is not easy to resist such a force, especially in water when our own body weight does not help us maintain stability. Finally, the pulling effect of a fast-moving train is explained by the same Bernoulli principle: a train at a speed of 50 km per hour drags a nearby person with a force of about 8 kg.
Phenomena associated with the “Bernoulli principle,” although very common, are little known among non-specialists. It will therefore be useful to dwell on it in more detail. Below we present an excerpt from an article on this topic published in a popular science magazine.
Bernoulli's principle and its consequences
The principle, first stated by Daniel Bernoulli in 1726, states that in a stream of water or air, the pressure is high if the speed is low, and the pressure is low if the speed is high. There are known limitations to this principle, but we will not dwell on them here.Rice. 69 illustrates this principle.
Air is blown through tube AB. If the cross-section of the tube is small, as in a, the air speed is high; where the cross section is large, as in b, the air speed is low. Where the speed is high, the pressure is low, and where the speed is low, the pressure is high. Due to the low air pressure in a, the liquid in tube C rises; at the same time, the strong air pressure in b forces the liquid in tube D to descend.
Figure 69. Illustration of Bernoulli's principle. In the narrowed part (a) of the AB tube, the pressure is less than in the wide part (b).
In Fig. 70 tube T is mounted on a copper disk DD; air is blown through tube T and then past the free disk dd. The air between the two disks has a high speed, but this speed quickly decreases as it approaches the edges of the disks, since the cross-section of the air flow quickly increases and the inertia of the air flowing from the space between the disks is overcome. But the pressure of the air surrounding the disk is high, since the speed is low, and the air pressure between the disks is small, since the speed is high. Therefore, the air surrounding the disk has greater impact on the disks, trying to bring them closer together, rather than the air flow between the disks, trying to push them apart; As a result, the dd disk sticks to the DD disk the more strongly, the stronger the air current in T.
Rice. 71 is analogous to Fig. 70, but only with water. The fast moving water on the DD disk is at a low level and rises to a higher level. high level calm water in the pool when it goes around the edges of the disk. Therefore, calm water under the disk has more high pressure, than moving water above the disk, causing the disk to rise. Rod P does not allow lateral displacement of the disc.
Figure 70. Experience with disks.
Figure 71. Disc DD is raised on rod P when a stream of water from the tank is poured onto it.
Rice. 72 depicts a light ball floating in a stream of air. The air stream hits the ball and prevents it from falling. When the ball jumps out of the jet, the surrounding air returns it back into the jet, since the pressure of the surrounding air, which has a low speed, is high, and the pressure of the air in the jet, which has a high speed, is small.
Rice. 73 represents two ships moving side by side in calm water, or, what amounts to the same thing, two ships standing nearby and streamlined by water. The flow is more confined in the space between the vessels, and the speed of the water in this space is greater than on either side of the vessels. Therefore, the water pressure between the ships is less than on both sides of the ships; the higher water pressure surrounding the ships brings them closer together. Sailors know very well that two ships sailing side by side are strongly attracted to each other.
Figure 72. Ball supported by a stream of air.
Figure 73. Two ships moving in parallel seem to attract each other.
Figure 74. As vessels move forward, vessel B turns its bow toward vessel A.
Figure 75. If air is blown between two light balls, they will come closer together until they touch.
A more serious case may occur when one ship follows another, as shown in Fig. 74. Two forces F and F, which bring the ships together, tend to turn them, and ship B turns towards A with considerable force. A collision in this case is almost inevitable, since the rudder does not have time to change the direction of the ship's movement.
The phenomenon described in connection with Fig. 73 can be demonstrated by blowing air between two light rubber balls suspended as shown in Fig. 75. If you blow air between them, they come closer and hit each other.
Purpose fish bladder
The following is usually said and written about the role played by the swim bladder of fish - it would seem quite plausible. In order to emerge from the depths to the surface layers of water, the fish inflates its swim bladder; then the volume of its body increases, the weight of the displaced water becomes greater than its own weight - and, according to the law of swimming, the fish rises upward. To stop rising or going down, she, on the contrary, compresses her swim bladder. The volume of the body, and with it the weight of the displaced water, decreases, and the fish sinks to the bottom according to Archimedes' law.This simplified idea of the purpose of the swim bladder of fish dates back to the times of scientists of the Florentine Academy (XVII century) and was expressed by Professor Borelli in 1685. For more than 200 years, it was accepted without objection, and managed to take root in school textbooks, and only through the works of new researchers (Moreau, Charbonel) was the complete inconsistency of this theory discovered,
The bubble undoubtedly has a very close connection with the swimming of fish, since fish whose bubble was artificially removed during experiments could stay in the water only by working hard with their fins, and when this work stopped, they fell to the bottom. What is his true role? Very limited: it only helps the fish stay at a certain depth, precisely at the one where the weight of the water displaced by the fish is equal to the weight of the fish itself. When the fish, by the action of its fins, falls below this level, its body, experiencing great external pressure from the water, contracts, squeezing the bubble; the weight of the displaced volume of water decreases and becomes less weight fish, and the fish falls uncontrollably. The lower it falls, the stronger the water pressure becomes (by 1 atmosphere for every 10 m lowering), the more the fish’s body is compressed and the more rapidly it continues to descend.
The same thing, only in reverse direction, occurs when the fish, having left the layer where it was in equilibrium, moves by the action of its fins to higher layers. Her body, freed from part of the external pressure and still bursting from the inside with a swim bladder (in which the gas pressure was until that moment in equilibrium with the pressure surrounding water), increases in volume and as a result floats higher. The higher the fish rises, the more its body swells and, consequently, the faster its further rise. The fish is not able to prevent this by “squeezing the bladder”, since the walls of its swim bladder are devoid of muscle fibers that could actively change its volume.
Perelman Ya.I. Interesting mechanics. Edited by R. Bonchkovsky - Cooperative Publishing House, 1933. - 241 p.
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This explains to us, among other things, why friction against a stationary body is considered in mechanics as a force, although it cannot cause any movement.
Friction is a force because it slows down movement. Such forces, which themselves cannot generate movement, but are only capable of slowing down already existing movement (or balancing other forces), are called “passive” in contrast to driving or active forces.”
Let us emphasize once again that bodies do not strive to remain at rest, but simply remain at rest. The difference here is the same as between a stubborn homebody who is difficult to get out of the apartment, and a person who happens to be at home, but is ready to leave the apartment at the slightest reason. Physical bodies by nature they are not at all “homebodies”; on the contrary, they are highest degree mobile, as it is enough to apply to free body even the most insignificant force - and it begins to move. The expression “the body strives to remain at rest” is also inappropriate because a body removed from a state of rest does not return to it by itself, but, on the contrary, forever retains the movement imparted to it (in the absence, of course, of forces interfering with the movement).
A considerable share of those misunderstandings that are associated with the law of inertia is due to this careless word “tends”, which has crept into most textbooks of physics and mechanics.
No less difficult for correct understanding is Newton's third law, which we now turn to consider.
ACTION AND REACTION
Wanting to “Open the door, you pull it towards you by the handle. The muscle of your arm, contracting, brings its ends closer together: it pulls the door and your torso with equal force
yudno to another. In this case, it is clearly clear that there are two forces acting between your body and the door, one applied to the door, the other to your body. The same thing, of course, happens when the door opens not towards you, but away from you: forces push the door and your body away.
What we observe here for muscular strength is true for any force in general, regardless of what its nature is. Each voltage acts in two opposite directions; it has, figuratively speaking, two ends (two forces): one is applied to the body on which, as we say, the force acts; the other is attached to the body, which we call active. What has been said is usually expressed in mechanics briefly - too briefly for clear understanding - like this: “action is equal to action.”
The meaning of this law is that all forces of nature are double forces. In each case of manifestation of the action of a force, you must imagine that somewhere in (another place there is another force equal to this one, but directed in the opposite side. These two forces certainly act between two points, trying to bring them closer together or push them apart.
Let you consider (Fig. 5) the forces /\ QwK that act on a weight suspended from a child’s
Rice. 5. Forces (P9 Q, R)1 acting on the children’s weight hot air balloon. Where are the opposing forces?
stuffy ball. The thrust P of the ball, the thrust Q of the rope and the weight Tv of the weight are seemingly single forces. But that's just
distraction from reality; in fact, for each of the three forces there is a force equal to it, but (opposite in direction. Namely, the force opposite to the force P is applied to balloon(Fig. 6, force F1) ; force opposite to force Q - acts on ru-KU (Qi) force opposite to force R - applied at the center globe(force /?, Fig. 6), because the weight is not only attracted by the Earth, but also attracts it itself.
One more important note. When we ask about the tension in a rope whose ends are stretched by a force of 1 kg, we are essentially asking about the price of 10<копеечной почтовой марки. Ответ содержится в самом вопросе: веревка на-кг. Сказать «веревка растягивается двумя
Rice. 6. Answer to the question in the previous figure: Pj9Q1Ji^-reacting forces.
pulled with a force of 1 by a force of 1 kg" or "the rope is subject to a tension of 1 kg" means to express literally the same thought.
“After all, there cannot be any other tension of 1 kg, except that which consists of two forces directed in opposite directions. Forgetting this, they often fall into gross mistakes, examples of which we will now give.
THE TWO HORSES PROBLEM
Two horses stretch a spring steelyard with a force of 100 kg each. What does the steelyard arrow show?
Many answer: 100 + 100 = 200 kg. The answer is incorrect. The forces of 100 kg with which horses pull cause
Rice. 7. Each horse pulls with a force of 100 kg. How much shows
spring bevman?
as we just saw, the tension is not 200, but only 100 kg.
Therefore, by the way, when the Magdeburg hemispheres were stretched by 8 horses in one direction and 8 in the opposite direction, one should not think that they were stretched by the force of 16 horses. In the absence of the opposing 8 horses, the remaining 8 would have produced absolutely no effect on the hemispheres. One figure of eight horses could be replaced simply by a wall.
* PROBLEM O
Rice. 8. Which boat will arrive first?