Pulling Physicist. Surface tension

Definition 1

Surface tension - a gust of a liquid to reduce its own free surface, that is, to reduce the excess of potential energy at the border of separation with the gaseous phase.

Not only solid physical bodies are equipped with elastic characteristics, but also the surface of the liquid itself. Everyone in his life has seen how a soapy film is stretched with a slight blowing of bubbles. The surface tension forces that arise in the soap film keep the certain period time for air, similar to how a rubber expanding tube retains air in a soccer ball.

Surface tension appears at the interface between the main phases, for example, gaseous and liquid, or liquid and solid. This is directly due to the fact that elementary particles of the surface layer of a liquid always experience different forces of attraction from the inside and outside.

The specified physical process can be considered on the example of a drop of water, where the liquid moves itself as if it were in an elastic shell. Here, the atoms of the surface layer of a liquid substance are attracted to their own internal neighbors more strongly than to external air particles.

In general, surface tension can be explained as an infinitesimal or elementary work $ \ sigma A $, which must be done to increase the total surface area of ​​the liquid by an infinitely small amount $ dS $ at a constant temperature $ dt $.

Mechanism of surface tension in liquids

Figure 2. Scalar positive. Author24 - online exchange of student papers

Liquid, unlike solids and gases, is not able to fill the entire volume of the vessel in which it was placed. A certain interface is formed between the vapor and the liquid substance, which acts under special conditions in comparison with another mass of liquid. Consider for more illustrative example two molecules $ A $ and $ B $. The $ A $ particle is inside the liquid itself, the $ B $ molecule is directly on its surface. The first element is uniformly surrounded by other atoms of the liquid, therefore, the forces acting on the molecule from the side of particles falling into the sphere of intermolecular interaction are always compensated, or, in other words, their resultant power is zero.

On the one hand, the $ B $ molecule is framed by liquid molecules, and on the other hand, by gas atoms, the total concentration of which is significantly lower than the union of elementary particles of a liquid. Since much more molecules act on the $ B $ molecule from the side of the liquid than from the side of an ideal gas, it is no longer possible to equate the resultant of all intermolecular forces to zero, since this parameter is directed into the volume of the substance. Thus, in order for a molecule to end up in the surface layer from the depth of the liquid, work should be done against uncompensated forces. This means that the atoms of the near-surface level, in comparison with the particles inside the liquid, are equipped with excess potential energy, which is called surface energy.

Surface tension coefficient

Figure 3. Surface stress. Author24 - online exchange of student papers

Definition 2

The surface tension coefficient is a physical indicator that characterizes a certain liquid and is numerically equal to the ratio of the surface energy to the total area of ​​the free medium of the liquid.

In physics, the basic unit for measuring the surface tension coefficient in the SI concept is (N) / (m).

The specified value directly depends on:

• the nature of the liquid (for “volatile elements such as alcohol, ether, gasoline, the coefficient of surface tension is much less than that of“ non-volatile - mercury, water);
• the temperature of the liquid substance (the higher the temperature, the lower the final surface tension);
• properties of an ideal gas bordering on a given liquid;
• the presence of stable surfactants such as washing powder or soap, which can reduce the surface tension.

Remark 1

It should also be noted that the surface tension parameter does not depend on the initial area of ​​the free medium of the liquid.

It is also known from mechanics that the unchanged states of the system always correspond to the minimum value of its internal energy. As a result of this physical process, a liquid body often takes on a form with a minimum surface. If the liquid is not affected by extraneous forces or their action is extremely small, its elements are shaped like a sphere in the form of a drop of water or a soap bubble. Water begins to behave in a similar way while in zero gravity. The fluid moves as if the factors that reduce this environment are acting tangentially to its main surface. These forces are called surface tension forces.

Consequently, the surface tension coefficient can also be defined as the main modulus of the surface tension force, which generally acts per unit length of the initial contour that bounds the free medium of the liquid. The presence of these parameters makes the surface of a liquid substance similar to a stretched elastic film, with the only difference that the invariable forces in the film directly depend on the area of ​​its system, and the surface tension forces themselves are able to work independently. If you put a small sewing needle on the surface of the water, the surface will bend and prevent it from drowning.

The action of an external factor can be described as the sliding of light insects, such as water striders, over the entire surface of water bodies. The foot of these arthropods deforms the water surface, thereby increasing its area. The result is a surface tension force that tends to reduce such a change in area. The resultant force will always be directed exclusively upward, while compensating for the effect of gravity.

The result of the action of surface tension

Under the influence of surface tension, small quantities of liquid media tend to take a spherical shape, which will ideally correspond to the smallest value environment... The approach to the spherical configuration is achieved the more, the weaker the initial forces of gravity, since in small drops the indicator of the surface tension force is much greater than the effect of gravity.

Surface tension is considered one of the most important characteristics of interfaces. It directly affects the formation of fine particles of physical bodies and liquids during their separation, as well as the fusion of elements or bubbles in mists, emulsions, foams, and adhesion processes.

Remark 2

Surface tension sets the shape of future biological cells and their main parts.

A change in the strength of this physical process affects phagocytosis and the processes of alveolar respiration. Due to this phenomenon, porous substances can retain a huge amount of liquid even from air vapor for a long time. Capillary phenomena, involving changes in the height of the liquid level in capillaries compared to the liquid level in a wider vessel, are very common. Through these processes, the rise of water in the soil, along the root system of plants, the movement of biological fluids through the system of small tubules and blood vessels is caused.

The liquid is state of aggregation a substance intermediate between gaseous and solid, therefore it has the properties of both gaseous and solid substances. Liquids, like solids, have a certain volume, and like gases, they take the form of a vessel in which they are located. Gas molecules are practically not connected with each other by the forces of intermolecular interaction. V in this case the average energy of the thermal motion of gas molecules is much greater than the average potential energy due to the forces of attraction between them, therefore the gas molecules scatter in different directions, and the gas occupies the entire volume provided to it.

In solids and liquids, the forces of attraction between molecules are already significant and keep the molecules at a certain distance from each other. In this case, the average energy of the chaotic thermal motion of molecules is less than the average potential energy due to the forces of intermolecular interaction, and it is not enough to overcome the forces of attraction between the molecules, therefore, solids and liquids have a certain volume.

X-ray structural analysis of liquids showed that the nature of the arrangement of liquid particles is intermediate between a gas and a solid. In gases, molecules move chaotically, so there is no pattern in their mutual disposition... For solids, the so-called long-range order in the arrangement of particles, i.e. their ordered arrangement, repeated over long distances. In liquids, the so-called close order in the arrangement of particles, i.e. their ordered arrangement, repeated at distances comparable to interatomic ones.

The theory of fluid has not yet been fully developed. Thermal motion in a liquid is explained by the fact that each molecule vibrates for some time about a certain equilibrium position, after which it jumps to a new position, which is at a distance of the order of interatomic distance from the initial one. Thus, the molecules of the liquid move rather slowly throughout the mass of the liquid, and diffusion is much slower than in gases. With an increase in the temperature of the liquid, the frequency of the vibrational motion increases sharply, the mobility of the molecules increases, which is the reason for the decrease in the viscosity of the liquid.

The attraction forces act on each liquid molecule from the side of the surrounding molecules, rapidly decreasing with distance, therefore, starting from a certain minimum distance, the attraction forces between the molecules can be neglected. This distance (approximately 10 -9 m) is called radius of molecular action r , and the sphere of radius r -sphere of molecular action.

Select a molecule inside the liquid A and draw a sphere of radius around it r(Figure 10.1). It is enough, according to the definition, to take into account the action on a given molecule of only those molecules that are inside the sphere

Figure 10.1. molecular action. The forces with which these molecules act on a molecule A, directed in different directions and, on average, are compensated; therefore, the resulting force acting on a molecule inside a liquid from the side of other molecules is zero. The situation is different if a molecule, for example a molecule V, located from the surface at a distance less than r. In this case, the sphere of molecular action is only partially located inside the liquid. Since the concentration of molecules in the gas located above the liquid is small compared to their concentration in the liquid, the resultant forces F applied to each molecule of the surface layer is not zero and is directed into the liquid. Thus, the resulting forces of all molecules of the surface layer exert a pressure on the liquid, called molecular(or internal). Molecular pressure does not act on a body placed in a liquid, since it is caused by forces acting only between the molecules of the liquid itself.

The total energy of liquid particles is the sum of the energy of their chaotic thermal motion and potential energy due to the forces of intermolecular interaction. It takes work to move a molecule from the depth of the liquid to the surface layer. This work is done at the expense kinetic energy molecules and goes to increase their potential energy. Therefore, the molecules of the surface layer of the liquid have a higher potential energy than the molecules inside the liquid. This additional energy that molecules in the surface layer of the liquid possess, called surface energy, proportional to the layer area Δ S:

Δ W=σ Δ S,(10.1)

where σ - coefficient of surface tension, defined as the density of the surface energy.

Since the equilibrium state is characterized by a minimum of potential energy, the liquid in the absence of external forces will take on such a shape that for a given volume it has a minimum surface, i.e. ball shape. Observing the smallest droplets suspended in the air, we can see that they really have the shape of balls, but somewhat distorted due to the action of the forces of gravity. Under zero gravity, a drop of any liquid (regardless of its size) has a spherical shape, which has been proven experimentally on spacecraft.

So, the condition for stable equilibrium of the liquid is the minimum surface energy. This means that the liquid for a given volume should have the smallest surface area, i.e. the liquid tends to reduce the free surface area. In this case, the surface layer of the liquid can be likened to a stretched elastic film in which tension forces act.

Consider a liquid surface bounded by a closed contour. Under the action of surface tension forces (they are directed tangentially to the surface of the liquid and perpendicular to the section of the contour on which they act), the surface of the fluid shrank and the contour in question moved. The forces acting from the side of the allocated area on the areas bordering it do the work:

Δ A = fΔ lΔ x,

where f = F /Δ l -surface tension force acting per unit length of the contour of the liquid surface. It is seen that Δ lΔ x= Δ S, those.

Δ A = fΔS.

This work is done by reducing the surface energy, i.e.

Δ Α =Δ W.

Comparison of the expressions shows that

i.e., the coefficient of surface tension σ is equal to the surface tension force per unit length of the contour bounding the surface. The unit of surface tension is newton per meter (N / m) or joule per square meter (J / m 2). Most liquids at a temperature of 300K have a surface tension of the order of 10 -2 –10 -1 N / m. The surface tension decreases with increasing temperature, as the average distances between liquid molecules increase.

Surface tension essentially depends on the impurities present in liquids. , weakening the surface tension of liquids are called surfactants (surfactants). The best known surfactant for water is soap. It greatly reduces its surface tension (from about 7.5 10 -2 up to 4.5 · 10 -2 N / m). Surfactants that lower the surface tension of water are also alcohols, ethers, oil, etc.

There are substances (sugar, salt) that increase the surface tension of a liquid due to the fact that their molecules interact with liquid molecules more strongly than liquid molecules with each other.

In construction, surfactants are used to prepare solutions used in the processing of parts and structures operating in adverse atmospheric conditions (high humidity, high temperatures, exposure to solar radiation, etc.).

Wetting phenomenon

It is known from practice that a drop of water spreads on glass and takes the shape shown in Figure 10.2, while mercury on the same surface turns into a somewhat oblate drop. In the first case, they say that the liquid wets hard surface, in the second - does not wet her. Wetting depends on the nature of the forces acting between the molecules of the surface layers of the contacting media. For a wetting liquid, the forces of attraction between liquid molecules and solid more than between the molecules of the liquid itself, and the liquid tends to increase

surface of contact with a solid. For a non-wetting liquid, the forces of attraction between the molecules of the liquid and the solid are less than between the molecules of the liquid, and the liquid tends to reduce the surface of its contact with the solid.

Three surface tension forces are applied to the line of contact of the three media (point 0 is its intersection with the plane of the drawing), which are directed tangentially inside the contact surface of the corresponding two media. These forces, per unit length of the line of contact, are equal to the corresponding surface tensions σ 12 , σ 13 , σ 23 . Injection θ between the tangents to the surface of a liquid and a solid is called edge angle. The condition for the equilibrium of the drop is the equality to zero of the sum of the projections of the surface tension forces on the direction of the tangent to the surface of the solid, i.e.

–σ 13 + σ 12 + σ 23 cos θ =0 (10.2)

cos θ =(σ 13 - σ 12)/σ 23 . (10.3)

It follows from the condition that the contact angle can be acute or obtuse, depending on the values σ 13 and σ 12 . If σ 13 >σ 12, then cos θ > 0 and angle θ sharp, i.e. liquid wets a solid surface. If σ 13 <σ 12, then cos θ <0 и угол θ – dull, i.e. the liquid does not wet the hard surface.

The contact angle satisfies condition (10.3) if

(σ 13 - σ 12)/σ 23 ≤1.

If the condition is not met, then a drop of liquid for no values θ cannot be in balance. If σ 13 >σ 12 +σ 23, then the liquid spreads over the surface of a solid, covering it with a thin film (for example, kerosene on the surface of glass), - takes place complete wetting(in this case θ =0).

If σ 12 >σ 13 +σ 23, then the liquid contracts into a spherical drop, in the limit having only one point of contact with it (for example, a drop of water on the surface of paraffin), - there is complete non-wetting(in this case θ =π).

Wetting and non-wetting are relative terms, i.e. a liquid that wets one solid surface does not wet another. For example, water wets glass but does not wet paraffin; mercury does not wet glass, but it does wet clean metal surfaces.

The phenomena of wetting and non-wetting have great importance in technology. For example, in the method of flotation concentration of ore (separation of ore from waste rock), finely crushed ore is shaken in a liquid that moistens the waste rock and does not wet the ore. Air is blown through this mixture, and then it settles. In this case, the particles of the rock moistened with the liquid sink to the bottom, and the grains of minerals "stick" to the air bubbles and float to the surface of the liquid. During the machining of metals, they are moistened with special liquids, which facilitates and accelerates the surface treatment.

In construction, the phenomenon of wetting is important for the preparation of liquid mixtures (putties, putties, mortars for laying bricks and preparing concrete). It is necessary that these liquid mixtures wet well the surfaces of the building structures on which they are applied. When selecting the components of mixtures, not only the contact angles for mixture-surface pairs are taken into account, but also the surface-active properties of liquid components.

The forces of attraction between molecules on the surface of a liquid keep them from moving outside of it.

The molecules of the liquid experience the forces of mutual attraction - in fact, it is thanks to this that the liquid does not instantly evaporate. The attraction forces of other molecules act on the molecules inside the liquid from all sides and therefore mutually balance each other. Molecules on the surface of a liquid have no neighbors outside, and the resulting attraction force is directed towards the inside of the liquid. As a result, the entire surface of the water tends to shrink under the influence of these forces. Taken together, this effect leads to the formation of the so-called surface tension force, which acts along the surface of the liquid and leads to the formation of an invisible, thin and elastic film on it.

One of the consequences of the surface tension effect is that to increase the surface area of ​​the liquid - its stretching - you need to do mechanical work to overcome surface tension forces. Consequently, if the liquid is left alone, it tends to take a shape in which its surface area will be minimal. Naturally, such a shape is a sphere, which is why raindrops in flight take an almost spherical shape (I say "almost" because in flight the droplets stretch slightly due to air resistance). For the same reason, water droplets on the body of a car covered with fresh wax collect into beads.

Surface tension forces are used in industry, in particular when casting spherical shapes such as shotguns. The droplets of molten metal are simply allowed to freeze on the fly when dropped from a sufficient height for this, and they themselves solidify in the form of balls before falling into the receiving container.

There are many examples of surface tension forces in action from our everyday life. Wind ripples on the surface of oceans, seas and lakes, and these ripples are waves in which the upward force of internal water pressure is balanced by the downward force of surface tension. These two forces alternate, and ripples are formed on the water, just as a wave is formed in the string of a musical instrument due to alternating stretching and compression.

Will the liquid collect in "beads" or spread evenly over a solid surface, depends on the ratio of the forces of intermolecular interaction in the liquid, causing surface tension, and the forces of attraction between the molecules of the liquid and the solid surface. In liquid water, for example, surface tension forces are due to hydrogen bonds between molecules ( cm. Chemical bonds). The surface of the glass is wetted with water, since the glass contains a lot of oxygen atoms, and water easily forms hydrogenic bonds not only with other water molecules, but also with oxygen atoms. If you lubricate the glass surface with fat, hydrogen bonds with the surface will not form, and water will collect into droplets under the influence of internal hydrogen bonds determining surface tension.

In the chemical industry, special wetting reagents are often added to water - surfactants, - preventing water from collecting into drops on any surface. They are added, for example, to liquid dishwasher detergents. Getting into the surface layer of water, the molecules of such reagents noticeably weaken the forces of surface tension, water does not collect into drops and does not leave dirty specks on the surface after drying ( cm.

(Monday, 21 September 2015 02:04)

Please tell me how many times a day to inhale Microhydrin powder?

#3

Tatyana, microhydrin powder is in capsules and it is consumed by mouth with water or by opening the capsule it is dissolved in water (do not inhale!). Dosages depending on your condition and what results you want to get

#4

Please tell me, when gluing the neutronic to the laptop panel, the corner of the neutronic fell on the loop, and so total area the neutronics was violated. Will this affect the work of the neutr?!

#5

Inga, the protective field is created up and to the right of the sticker itself, therefore it must be located in the lower left corner of the monitor. If, as I understand it, you pasted it on a plane with a small relief, then this does not affect ego efficiency. I remind you that re-sticking is not allowed, since peeling off destroys the antenna array inside the sticker

#6

Hello! Why, as soon as I start drinking coral water, stomach attacks begin to torment, as if I drank acid. What is the reason for this?

#7

Coral water is slightly alkaline (far from acid!). I have not met with such a reaction. You may have some kind of gastrointestinal disease. Contact the person who recommended you

#8

Hello! Please tell me about the following: you have to sleep at a short distance from the outlet, 50 centimeters, it is strictly parallel to the head, but I do not feel any discomfort at all, does this mean that there is no harmful effect on the body? I am very afraid of oncology.

#9

Alexey, you don't need to be afraid of anything especially "very", your fear only attracts events. If translated into the language of the subconscious, it means "I want to experience this."
All electrical wiring in the apartment creates electromagnetic radiation (background), but this does not mean that it is worth giving up the benefits of civilization (if possible). In addition to this, there are also radio waves, mobile and special communications, ... and this is constantly present in our life! We cannot influence these factors even if we give up a computer, a phone, ... all the same it is in the neighbors the same wifi.
But it is in our power to use personal protective equipment (if we consider the impact external factors). But more importantly, what is (in most cases) the cause of all problems and diseases is the internal state of the body. By regularly cleansing and, if possible (consciously) not clogging up the body with harmful food and drinks, giving it all that is useful, you will live a long and happy life ( positive emotions and no one canceled thinking :))!

#10

Please help me to contact you

#11

Hello Svetlana, contact details
Email: [email protected]
Skype: viktorcoral
https://www.facebook.com/viktorcoral
https://vk.com/viktorcoral
https://twitter.com/viktorcoral_if
If you are from Ukraine tel 0673447004

#12

Alena Arbenina (Friday, 30 June 2017 12:52)

Hello, thanks for this useful information, it turns out that despite various factors (such as ecology), we can still do a lot for our own health. As I learned here https://goal-life.com/page/kniga/idea/koncepciya-zdorovya-mihail-fomin, health is a natural state for humans, therefore it is important to preserve the potential obtained at birth.

#13

Natalia (Friday, 12 January 2018 21:02)

Interesting information... Thank you

#14

Good evening! I started accepting your products from yesterday. Now sleep is gone. What to do?

#15

Where to get Border Water.

#16

Elena, border water is no longer on sale

#17

"Minerals, in mineralized water, are in the form inorganic salts and therefore are not absorbed by the body. "
How is it, excuse me? Dare to drink potassium cyanide? After all, in your opinion, it is not assimilated by the body. In no case do I have a goal of offending you. But such statements cause distrust of the author and make him doubt everything he said. He lied about one thing, most likely he will lie about the rest.

#18

An assimilator can be used for type 2 diabetes and prostate cancer

#19

Alexander, you can, these are plant enzymes that will relieve the load on the pancreas and improve digestion, respectively, there will be less toxic waste in the intestines.
With such diagnoses, more radical actions are needed.

#20

Hello. In the lecture "skin is a mirror of the body", Olga Alekseevna talked about how to take an artichoke, the sound is loud, but not intelligible. Please tell me how to use this N1 cleaner.

#21

Hello, my husband was diagnosed with hemorrhage. From your words, I still did not understand how it is treated and what is better to eat. Thanks in advance for the answer.

#22

Good day to everyone! I have been using Coral Club products for a long time, I have not observed any side effects in my health. For two years I have been saving money from my pension to buy Vitastik. Prior to that, I did blood diagnostics on a dark-field microscope (called an analysis of a living drop of blood-hemoscritis, they will not do it in any polyclinic, only in medical centers, and even then not in all. This analysis is not cheap, so the head of the medical center said that for all three years of the existence of the center for the FIRST TIME he sees a person whose blood MOVES, and not worth jelly and porridge, like everyone else, but all thanks to H-500, or, more simply, microhydrin and thawed water, or "live", which I do it with a special device. At first I also had headaches and pressure, this body was getting rid of toxins and toxins accumulated over life. Digestion, blood composition, skin color, mood, sleep, etc. improved. So, people, DRINK WATER !!!, not mineral water, juices, coffee and other nonsense, and, especially, during or after a meal, fewer "butriks", but more water and movement so that the lymph does not stand, and the water treated by Vitastik will give it life and energy, like from a mountain stream. You will not see this, but you will feel it when you drink At the same time, 50 ml of tap water, and then the same amount treated with vitastik, or with the addition of H-500. Do any of you remember how sweet the snow or icicles tasted that we all ate in childhood? So, water treated with Vitastic is the very taste of childhood. Do not be afraid, but trust yourself and your body, listen to yourself and him, he is not a fool, and knows when, what and how much he wants, stop poisoning him with pills, cigarettes, alcohol and many others, lead a healthy lifestyle and think positively, and everything will be fine with you, inside, and outside!

#23

Yes, even for those who do not believe, or do not know, watch the video on youtub about water, it is called, "water is alive and dead", it was shown on the Russia channel in 2014, and also Olga Butakova - video "water, treated with a vitalizer. "You can add Emoto Masaru here, and Neumyvakin, and Svetla water, in general, go for it, whoever seeks and wants, always finds. Good luck and health to everyone!

#24

And after a year of regular use of water and supplements prescribed by a doctor, my pressure jumps and my pulse goes off scale to 110 beats and my heart hurts. They say that the sand is coming, you have to be patient .. I had to increase the dose of the drug from the pressure 4 times and drink pills to slow down the heart rhythm. I've been putting up with it for the third month already.

#25

Omega 3 is a very important supplement, especially for women! Now, with active sports, I drink a course of Evalar triple omega 3 and in addition, once a week I eat at least fish (I prefer red). The skin pleases with its condition)

Surface tension describes the ability of a fluid to resist gravity. For example, water on a tabletop forms droplets as water molecules are attracted to each other, which counteracts gravity. It is due to surface tension that heavier objects, such as insects, can be held on the surface of the water. Surface tension is measured in force (N) divided by unit length (m), or energy per unit area. The force with which water molecules interact (cohesive force) creates tension, resulting in droplets of water (or other liquids). Surface tension can be measured with a few simple items found in almost every home and a calculator.

Steps

Using the rocker

Write down the equation for surface tension. In this experiment, the equation for determining the surface tension is as follows: F = 2Sd, where F- force in newtons (N), S- surface tension in newtons per meter (N / m), d is the length of the needle used in the experiment. Let us express the surface tension from this equation: S = F / 2d.

• The force will be calculated at the end of the experiment.
• Before starting the experiment, use a ruler to measure the length of the needle in meters.

1. Build a small rocker arm. This experiment uses a rocker arm and a small needle that floats on the surface of the water to determine the surface tension. It is necessary to carefully consider the construction of the rocker arm, since the accuracy of the result depends on it. You can use various materials, the main thing is to make a horizontal bar from something hard: wood, plastic or thick cardboard.

   • Determine the center of the rod (for example, a straw or plastic ruler) that you are going to use as a crossbar, and drill or punch a hole in this place; this will be the fulcrum of the crossbar, at which it will rotate freely. If you are using a plastic straw, simply pierce it with a pin or nail.
   • Drill or punch holes in the ends of the crossbeam so that they are equally spaced from the center. Pass the threads through the holes to hang the weight cup and needle.
   • If necessary, support the beam with books or other solid enough objects to keep the beam level. It is necessary that the crossbar rotates freely around a nail or rod stuck in its middle.

2. Take a piece of aluminum foil and roll it up into a box or saucer shape. It is not at all necessary that this saucer has a regular square or round shape. You will fill it with water or some other weight, so make sure it can support the weight.

   • Hang a tin foil box or saucer from one end of the bar. Make small holes along the edges of the saucer and thread through them so that the saucer hangs from the bar.

3. Hang a needle or paperclip from the other end of the bar so that it is horizontal. Tie a needle or paperclip horizontally to the thread that hangs from the other end of the bar. For the experiment to be successful, it is necessary to position the needle or paper clip exactly horizontally.

4. Place something on the bar, such as plasticine, to balance the aluminum foil container. Before starting the experiment, it is necessary to ensure that the crossbar is located horizontally. The foil saucer is heavier than the needle, so the bar on the side of the saucer will drop down. Attach enough plasticine to the opposite side of the bar so that it is horizontal.

   • This is called balancing.

5. Place the dangling needle or paperclip in a container of water. This step will require extra effort to position the needle on the surface of the water. Make sure that the needle does not sink into the water. Fill a container with water (or another liquid of unknown surface tension) and place it under the hanging needle so that the needle is directly on the surface of the liquid.

   • Make sure that the rope holding the needle stays in place and is sufficiently tight.

6. Weigh a few pins or a small amount of measured drops of water on a small scale. You will add one pin or one drop of water to the aluminum saucer on the rocker. In this case, it is necessary to know the exact weight at which the needle will come off the surface of the water.

   • Count the number of pins or water droplets and weigh them.
   • Determine the weight of one pin or drop of water. To do this, divide the total weight by the number of pins or drops.
   • Suppose 30 pins weigh 15 grams, then 15/30 = 0.5, that is, one pin weighs 0.5 grams.

7. Add pins or water droplets one at a time in an aluminum foil saucer until the needle comes off the surface of the water. Add one pin or a drop of water gradually. Watch the needle carefully so as not to miss the moment when, after the next increase in the weight, it will come off the water. Once the needle comes off the surface of the liquid, stop adding pins or water droplets.

   • Count the number of pins or water droplets that caused the needle at the opposite end of the bar to come off the surface of the water.
   • Write down the result.
   • Repeat the experiment several (5 or 6) times to get more accurate results.
   • Calculate the average of the results obtained. To do this, add the number of pins or drops in all experiments and divide the total by the number of experiments.

8. Convert the number of pins to strength. To do this, multiply the number of grams by 0.00981 N / g. To calculate the surface tension, you need to know the force it took to lift the needle off the water surface. Since you counted the weight of the pins in the previous step to determine the force, you just need to multiply that weight by 0.00981 N / g.

   • Multiply the number of pins in the saucer by the weight of one pin. For example, if you put in 5 pins each weighing 0.5 grams, their total weight is 0.5 grams / pin = 5 x 0.5 = 2.5 grams.
   • Multiply the number of grams by a factor of 0.00981 N / a: 2.5 x 0.00981 = 0.025 N.

9. Plug these values ​​into the equation and find the value you are looking for. The results obtained during the experiment can be used to determine the surface tension. Just plug in the values ​​you find and calculate the result.

   • Let's say in the example above, the needle length is 0.025 meters. Substituting the values ​​into the equation and we get: S = F / 2d = 0.025 N / (2 x 0.025) = 0.05 N / m. Thus, the surface tension of the liquid is 0.05 N / m.