Surface tension of water. Lesson on the topic "surface tension" Increase surface tension

In this lesson, we will talk about liquids and their properties. Liquids have a number of interesting properties and their manifestations. One such property will be discussed in this lesson.

In the world around us, along with gravity, elasticity and friction, there is another force that we usually pay little or no attention to. This force is relatively small, its action never causes impressive effects. However, we cannot pour water into a glass, we cannot do anything at all with any liquid without setting in motion the forces that we will talk about. These are surface tension forces.

The ability of a liquid to contract its surface is called surface tension.

surface tension force called the force that acts along the surface of the liquid perpendicular to the line limiting this surface, and tends to reduce it to a minimum.

The surface tension force is determined by the formula, the product of sigma and el. Where sigma is the surface tension coefficient, el is the length of the wetting perimeter.

Let us dwell on the concept of “coefficient of surface tension” in more detail.

The surface tension coefficient is numerically equal to the force acting per unit length of the wetting perimeter and directed perpendicular to this perimeter.

Also, the coefficient of surface tension of a liquid is a physical quantity that characterizes a given liquid and is equal to the ratio of surface energy to the surface area of the liquid.

The molecules of the surface layer of a liquid have an excess of potential energy compared to the energy that these molecules would have if they were inside the liquid.

surface energy is the excess potential energy possessed by molecules on the liquid surface.

The coefficient of surface tension is measured in newtons divided by a meter.

Let us discuss what the coefficient of surface tension of a liquid depends on. To begin with, let us recall that the surface tension coefficient characterizes the specific energy of the interaction of molecules, which means that the factors that change this energy will also change the surface tension coefficient of the liquid.

So, the surface tension coefficient depends on:

1. The nature of the liquid (for "volatile" liquids, such as ether, alcohol and gasoline, the surface tension is less than that of "non-volatile" ones - water, mercury and liquid metals).

2. Temperature (the higher the temperature, the lower the surface tension).

3. The presence of surfactants that reduce surface tension (surfactants), such as soap or washing powder.

4. Properties of a gas adjoining a liquid.

Surface tension forces determine the shape and properties of liquid droplets, a soap bubble. These forces keep a steel needle and a water strider insect on the surface of the water, and keep moisture on the surface of the fabric.

You can verify the existence of surface tension forces using a simple experiment. If a thread is tied to the wire ring in two places, and so that the length of the thread is somewhat greater than the length of the chord connecting the points of attachment of the thread, and dip the wire ring in soapy water, the soap film will tighten the entire surface of the ring and the thread will lie on the soap film. If the film is now torn on one side of the thread, the soapy film remaining on the other side of the thread will shrink and stretch the thread. Why did this happen? The fact is that the soap solution remaining on top, that is, the liquid, tends to reduce its surface area. Thus, the thread is pulled up.

Consider an experiment confirming the desire of a liquid to reduce the surface of contact with air or vapor of this liquid.

An interesting experiment was carried out by the Belgian physicist Joseph Plateau. He argues that if a drop is in conditions where the main influence on its shape is exerted by surface tension forces, it takes the form with the smallest surface, that is, spherical.

In this lesson, we will talk about liquids and their properties. From the point of view of modern physics, liquids are the most difficult subject of research, because, compared to gases, one can no longer speak of a negligible interaction energy between molecules, and compared to solids, one cannot speak of an ordered arrangement of liquid molecules (there is no long-range order in a liquid) . This leads to the fact that liquids have a number of interesting properties and their manifestations. One such property will be discussed in this lesson.

First, let's discuss the special properties that the molecules of the near-surface layer of a liquid have in comparison with the molecules in the bulk.

Rice. 1. The difference between the molecules of the near-surface layer and the molecules in the bulk of the liquid

Consider two molecules A and B. Molecule A is inside the liquid, molecule B is on its surface (Fig. 1). Molecule A is surrounded by other liquid molecules evenly, so the forces acting on molecule A from molecules falling into the sphere of intermolecular interaction are compensated, or their resultant is zero.

What happens to the molecule B, which is located at the surface of the liquid? Recall that the concentration of gas molecules that is above the liquid is much less than the concentration of liquid molecules. Molecule B is surrounded on one side by liquid molecules, and on the other side by highly rarefied gas molecules. Since many more molecules act on it from the side of the liquid, the resultant of all intermolecular forces will be directed inside the liquid.

Thus, in order for a molecule to get from the depth of the liquid to the surface layer, it is necessary to perform work against uncompensated intermolecular forces.

Recall that work is the change in potential energy, taken with a minus sign.

This means that the molecules of the near-surface layer, in comparison with the molecules inside the liquid, have excess potential energy.

This excess energy is a component of the internal energy of the fluid and is called surface energy. It is designated as, and is measured, like any other energy, in joules.

Obviously, the larger the surface area of the liquid, the more such molecules that have excess potential energy, and hence the greater the surface energy. This fact can be written as the following relation:

where is the surface area, and is the proportionality factor, which we will call surface tension, this coefficient characterizes one or another liquid. Let us write down a rigorous definition of this quantity.

The surface tension of a liquid (coefficient of surface tension of a liquid) is a physical quantity that characterizes a given liquid and is equal to the ratio of surface energy to the surface area of the liquid

The coefficient of surface tension is measured in newtons divided by a meter.

So, the surface tension coefficient depends on:

1. The nature of the liquid (for "volatile" liquids, such as ether, alcohol and gasoline, the surface tension is less than that of "non-volatile" - water, mercury and liquid metals).

2. Temperature (the higher the temperature, the lower the surface tension).

3. The presence of surfactants that reduce surface tension (surfactants), such as soap or washing powder.

4. Properties of a gas adjoining a liquid.

Note that the surface tension coefficient does not depend on the surface area, since for one individual near-surface molecule it is absolutely unimportant how many of the same molecules are around. Pay attention to the table, which shows the surface tension coefficients of various substances, at a temperature:

Table 1. Coefficients of surface tension of liquids at the boundary with air, at

So, the molecules of the near-surface layer have excess potential energy compared to the molecules in the bulk of the liquid. In the course of mechanics, it was shown that any system tends to a minimum of potential energy. For example, a body thrown from a certain height will tend to fall down. In addition, you feel much more comfortable lying down, because in this case the center of mass of your body is located as low as possible. What does the desire to reduce its potential energy in the case of a liquid lead to? Since the surface energy depends on the surface area, it means that it is energetically unfavorable for any liquid to have a large surface area. In other words, in the free state, the liquid will tend to minimize its surface.

This is easy to verify by experimenting with a soap film. If a wire frame is dipped into a soapy solution, then a soap film is formed on it, and the film acquires such a shape that its surface area is minimal (Fig. 2).

Rice. 2. Figures from a soapy solution

You can verify the existence of surface tension forces using a simple experiment. If a thread is tied to the wire ring in two places, and in such a way that the length of the thread is somewhat greater than the length of the chord connecting the points of attachment of the thread, and the wire ring is dipped in soap solution (Fig. 3a), the soap film will tighten the entire surface of the ring and the thread will lie on soap film. If now the film is broken on one side of the thread, the soap film remaining on the other side of the thread will shrink and stretch the thread (Fig. 3b).

Rice. 3. Experiment to detect surface tension forces

Why did this happen? The fact is that the soap solution remaining on top, that is, the liquid, tends to reduce its surface area. Thus, the thread is pulled up.

So, we are convinced of the existence of the surface tension force. Now let's learn how to calculate it. To do this, let's do a thought experiment. Let us lower a wire frame, one of the sides of which is movable, into the soapy solution (Fig. 4). We will stretch the soap film, acting on the movable side of the frame with force . There are thus three forces acting on the crossbar - an external force and two surface tension forces acting along each surface of the film. Using Newton's second law, we can write that

Rice. 4. Calculation of the surface tension force

If, under the action of an external force, the crossbar moves a distance , then this external force will do work

Naturally, due to the performance of this work, the surface area of the film will increase, which means that the surface energy will also increase, which we can determine through the surface tension coefficient:

The change in area, in turn, can be determined as follows:

where is the length of the movable part of the wire frame. Given this, we can write that the work of the external force is equal to

Equating the right parts in (*) and (**), we obtain an expression for the surface tension force:

Thus, the surface tension coefficient is numerically equal to the surface tension force that acts per unit length of the line that bounds the surface

So, we have once again seen that the liquid tends to take such a shape that its surface area is minimal. It can be shown that for a given volume, the surface area will be minimal for a sphere. Thus, if no other forces act on the fluid or their action is small, the fluid will tend to take on a spherical shape. So, for example, water will behave in zero gravity (Fig. 5) or soap bubbles (Fig. 6).

Rice. 5. Water in zero gravity

Rice. 6. Soap bubbles

The presence of surface tension forces can also explain why a metal needle "lies" on the surface of the water (Fig. 7). The needle, which is carefully placed on the surface, deforms it, thereby increasing the area of this surface. Thus, a surface tension force arises, which tends to reduce such a change in area. The resultant force of surface tension will be directed upward, and it will compensate for the force of gravity.

Rice. 7. Needle on the surface of the water

The principle of operation of the pipette can be explained in the same way. The droplet, on which the force of gravity acts, is pulled down, thereby increasing its surface area. Naturally, surface tension forces arise, the resultant of which is opposite to the direction of gravity, and which do not allow the droplet to stretch (Fig. 8). When you press down on the pipette's rubber cap, you create extra pressure that helps with gravity, causing the drop to fall down.

Rice. 8. How the pipette works

Let's take another example from everyday life. If you dip a paint brush into a glass of water, its hairs will fluff up. If you now take this brush out of the water, you will notice that all the hairs are stuck to each other. This is due to the fact that the surface area of the water adhering to the brush will then be minimal.

And one more example. If you want to build a dry sand castle, you are unlikely to succeed, since the sand will crumble under the influence of gravity. However, if you wet the sand, it will retain its shape due to the surface tension of the water between the sand grains.

Finally, we note that the theory of surface tension helps to find beautiful and simple analogies when solving more complex physical problems. For example, when you need to build a light and at the same time strong structure, the physics of what happens in soap bubbles comes to the rescue. And it was possible to build the first adequate model of the atomic nucleus by likening this atomic nucleus to a drop of charged liquid.

Bibliography

G. Ya. Myakishev, B. B. Bukhovtsev, N. N. Sotsky. "Physics 10". - M.: Education, 2008.
Ya. E. Geguzin "Bubbles", Kvant Library. - M.: Nauka, 1985.
B. M. Yavorsky, A. A. Pinsky "Fundamentals of Physics" vol. 1.
G. S. Landsberg "Elementary textbook of physics" vol. 1.

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Homework

By solving the tasks for this lesson, you will be able to prepare for questions 7,8,9 of the GIA and questions A8, A9, A10 of the Unified State Examination.
Gelfgat I.M., Nenashev I.Yu. "Physics. Collection of problems grade 10 "5.34, 5.43, 5.44, 5.47 ()
Based on problem 5.47, determine the coefficient of surface tension of water and soap solution.

List of questions and answers

Question: Why does surface tension change with temperature?

Answer: As the temperature increases, the molecules of the liquid begin to move faster, and therefore, the molecules more easily overcome the potential forces of attraction. This leads to a decrease in the surface tension forces, which are potential forces that bind the molecules of the near-surface layer of the liquid.

Question: Does the coefficient of surface tension depend on the density of the liquid?

Answer: Yes, it does, because the energy of the molecules of the near-surface layer of the liquid depends on the density of the liquid.

Question: What are the ways to determine the surface tension coefficient of a liquid?

Answer: In the school course, two methods are studied for determining the coefficient of surface tension of a liquid. The first is the wire tearing method, its principle is described in problem 5.44 from the homework, the second is the drop counting method, described in problem 5.47.

Question: Why do soap bubbles collapse after a while?

Answer: The fact is that after a while, under the action of gravity, the bubble becomes thicker at the bottom than at the top, and then, under the influence of evaporation, collapses at some point. This leads to the fact that the entire bubble, like a balloon, collapses under the action of uncompensated surface tension forces.

The most characteristic property of a liquid, which distinguishes it from a gas, is that at the boundary with a gas, the liquid forms a free surface, the presence of which leads to the appearance of a special kind of phenomena called surface. They owe their appearance to the special physical conditions in which the molecules are located near the free surface.

Attractive forces act on each liquid molecule from the molecules surrounding it, located at a distance of about 10 -9 m from it (radius of molecular action). per molecule M 1 located inside the liquid (Fig. 1), forces from the same molecules act, and the resultant of these forces is close to zero.

For molecules M 2 resultant forces are nonzero and are directed inside the liquid, perpendicular to its surface. Thus, all liquid molecules in the surface layer are drawn into the liquid. But the space inside the liquid is occupied by other molecules, so the surface layer creates pressure on the liquid (molecular pressure).

To move a molecule M 3 located directly under the surface layer, on the surface, it is necessary to perform work against the forces of molecular pressure. Therefore, the molecules of the surface layer of the liquid have additional potential energy compared to the molecules inside the liquid. This energy is called surface energy.

Obviously, the larger the free surface area, the greater the surface energy. Let the free surface area change by Δ S, while the surface energy changed by $~\Delta W_p = \sigma \cdot \Delta S$, where σ is the surface tension coefficient. Since for this change it is necessary to do work

$~A = \Delta W_p ,$ then $~A = \sigma \cdot \Delta S .$

Hence $~\sigma = \dfrac(A)(\Delta S)$ .

The SI unit for surface tension is the joule per square meter (J/m2).

- a value numerically equal to the work done by molecular forces when the area of the free surface of the liquid changes by 1 m 2 at a constant temperature.

Since any system, left to itself, tends to take a position in which its potential energy is the smallest, the liquid exhibits a tendency to reduce the free surface. The surface layer of the liquid behaves like a stretched rubber film, i.e. all the time strives to reduce its surface area to the minimum dimensions possible for a given volume.

For example, a drop of liquid in a state of weightlessness has a spherical shape.

Surface tension

The property of the surface of a liquid to shrink can be interpreted as the existence of forces tending to shorten this surface. Molecule M 1 (Fig. 2), located on the surface of the liquid, interacts not only with molecules located inside the liquid, but also with molecules located on the surface of the liquid, located within the sphere of molecular action. For a molecule M 1 the resultant $~\vec R$ of molecular forces directed along the free surface of the liquid is equal to zero, and for a molecule M 2 located at the boundary of the liquid surface, $~\vec R \ne 0$ and $~\vec R$ directed along the normal to the boundaries of the free surface and tangentially to the liquid surface itself.

The resultant of the forces acting on all molecules located on the boundary of the free surface is the force surface tension. In general, it acts in such a way that it tends to reduce the surface of the liquid.

It can be assumed that the surface tension force $~\vec F$ is directly proportional to the length l the boundaries of the surface layer of the liquid, because in all parts of the surface layer of the liquid the molecules are in the same conditions:

$~F \sim l .$

Indeed, consider a vertical rectangular frame (Fig. 3, a, b), the movable side of which is balanced. After removing the frame from the soap film solution, the movable part moves from the position 1 into position 2 . Taking into account that the film is a thin layer of liquid and has two free surfaces, we find the work done when moving the crossbar over a distance h = a 1 ⋅ a 2: A = 2F⋅h, Where F- the force acting on the frame from the side of each surface layer. On the other hand, $~A = \sigma \cdot \Delta S = \sigma \cdot 2l \cdot h$.

Therefore, $~2F \cdot h = \sigma \cdot 2l \cdot h \Rightarrow F = \sigma \cdot l$, whence $~\sigma = \dfrac Fl$.

According to this formula, the SI unit for surface tension is newton per meter (N/m).

Surface tension coefficientσ is numerically equal to the surface tension force acting per unit length of the boundary of the free surface of the liquid. The surface tension coefficient depends on the nature of the liquid, on the temperature and on the presence of impurities. As the temperature increases, it decreases.

At the critical temperature, when the distinction between liquid and vapor disappears, σ = 0.

Impurities generally reduce (some increase) the surface tension coefficient.

Thus, the surface layer of a liquid is, as it were, an elastic stretched film that covers the entire liquid and tends to collect it into one "drop". Such a model (elastic stretched film) makes it possible to determine the direction of surface tension forces. For example, if a film is stretched under the action of external forces, then the surface tension force will be directed along the surface of the liquid against stretching. However, this state differs significantly from the tension of an elastic rubber film. An elastic film is stretched by increasing the distance between the particles, while the tension force increases, while stretching the liquid film, the distance between the particles does not change, and the increase in the surface is achieved as a result of the transition of molecules from the liquid to the surface layer. Therefore, with an increase in the surface of the liquid, the surface tension force does not change (it does not depend on the surface area).

wetting

In the case of contact with a solid body, the cohesion forces of liquid molecules with solid body molecules begin to play a significant role. The behavior of a liquid will depend on which is greater: the adhesion between the molecules of the liquid or the adhesion of the molecules of the liquid to the molecules of the solid.

wetting- a phenomenon that occurs as a result of the interaction of liquid molecules with solid molecules. If the attractive forces between the molecules of a liquid and a solid are greater than the forces of attraction between the molecules of a liquid, then the liquid is called wetting; if the attraction forces of the liquid and the solid are less than the forces of attraction between the molecules of the liquid, then the liquid is called non-wetting this body.

The same liquid can be wetting and non-wetting with respect to different bodies. So, water wets glass and does not wet a greasy surface, mercury does not wet glass, but wets copper.

Wetting or non-wetting of the walls of the vessel in which it is located by a liquid affects the shape of the free surface of the liquid in the vessel. If a large amount of liquid is poured into a vessel, then the shape of its surface is determined by the force of gravity, which provides a flat and horizontal surface. However, near the walls, the phenomenon of wetting and non-wetting leads to a curvature of the liquid surface, the so-called edge effects.

The quantitative characteristic of edge effects is contact angleθ is the angle between the plane tangent to the surface of the liquid and the surface of the solid. There is always liquid inside the contact angle (Fig. 4, a, b). When wetted, it will be sharp (Fig. 4, a), and when not wetted, it will be blunt (Fig. 4, b). In a school physics course, only complete wetting (θ = 0º) or complete non-wetting (θ = 180º) is considered.

The forces associated with the presence of surface tension and directed tangentially to the surface of the liquid, in the case of a convex surface, give the resultant force directed inside the liquid (Fig. 5, a). In the case of a concave surface, the resulting force is directed, on the contrary, towards the gas adjoining the liquid (Fig. 5, b).

If the wetting liquid is on the open surface of a solid body (Fig. 6, a), then it spreads over this surface. If there is a non-wetting liquid on the open surface of a solid body, then it takes a shape close to a spherical one (Fig. 6, b).

Wetting is important both in everyday life and in industry. Good wetting is necessary when dyeing, washing, processing photographic materials, applying paint and varnish coatings, when gluing materials, when soldering, in flotation processes (enrichment of ores with valuable rock). Conversely, when constructing waterproofing devices, materials that are not wetted by water are needed.

Capillary phenomena

The curvature of the surface of the liquid at the edges of the vessel is especially clearly seen in narrow tubes, where the entire free surface of the liquid is curved. In tubes with a narrow cross section, this surface is part of a sphere, it is called meniscus. A wetting liquid has a concave meniscus (Fig. 7, a), while a non-wetting liquid has a convex one (Fig. 7, b). Since the surface area of the meniscus is greater than the cross-sectional area of the tube, the curved surface of the liquid tends to straighten out under the action of molecular forces.

Surface tension forces create additional (Laplacian) pressure under a curved liquid surface.

If the surface of the liquid concave, then the surface tension force is directed out of the liquid (Fig. 8, a), and the pressure under the concave surface of the liquid is less than under the flat one by $~p = \dfrac(2 \sigma )(R)$. If the surface of the liquid convex, then the surface tension force is directed inside the liquid (Fig. 8, b), and the pressure under the convex surface of the liquid is greater than under the flat one by the same value.

Rice. 8

This formula is a special case of the Laplace formula, which determines the overpressure for an arbitrary liquid surface of double curvature:

$~p = \sigma \cdot \left(\dfrac(1)(R_1) + \dfrac(1)(R_2) \right),$

Where R 1 and R 2 - radii of curvature of any two mutually perpendicular normal sections of the liquid surface. The radius of curvature is positive if the center of curvature of the corresponding section is inside the fluid, and negative if the center of curvature is outside the fluid. For a cylindrical surface ( R 1 = l; R 2 = ∞) overpressure $~p = \dfrac(\sigma)(R)$ .

If we place a narrow tube ( capillary) at one end into a liquid poured into a wide vessel, then due to the presence of the Laplacian pressure force, the liquid in the capillary rises (if the liquid is wetting) or falls (if the liquid is not wetting) (Fig. 9, a, b), since under the flat surface of the liquid in there is no excess pressure in a wide vessel.

The phenomena of a change in the height of the liquid level in capillaries compared to the liquid level in wide vessels are called capillary phenomena.

The liquid in the capillary rises or falls to such a height h, at which the force of the hydrostatic pressure of the liquid column is balanced by the force of excess pressure, i.e.

$~\dfrac(2 \sigma)(R) = \rho \cdot g \cdot h .$

Whence $~h = \dfrac(2 \sigma)(\rho \cdot g \cdot R)$. If wetting is not complete θ ≠ 0 (θ ≠ 180°), then, as calculations show, $~h = \dfrac(2 \sigma)(\rho \cdot g \cdot R) \cdot \cos \theta$.

Capillary phenomena are very common. The rise of water in the soil, the system of blood vessels in the lungs, the root system in plants, the wick and blotting paper are capillary systems.

Literature

Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Proc. allowance for institutions providing general. environments, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsia i vykhavanne, 2004. - C. 178-184.

Definition 1

Surface tension is the rush of a liquid to reduce its own free surface, that is, to reduce the excess potential energy at the boundary of separation from the gaseous phase.

Not only solid physical bodies are equipped with elastic characteristics, but also the surface of the liquid itself. Everyone in their life has seen how a soap film stretches with a little blowing bubbles. Surface tension forces that occur in a soap film hold air for a certain period of time, similar to how a stretched rubber bladder holds air in a soccer ball.

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

This physical process can be considered on the example of a water drop, 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 $\sigma A$ that must be done to increase the total surface area of a liquid by an infinitesimal amount $dS$ at a constant temperature $dt$.

The mechanism of surface tension in liquids

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

A 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 operates under special conditions compared to another mass of liquid. Consider, for a 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, so the forces acting on the molecule from the particles falling into the sphere of intermolecular interaction are always compensated, or, in other words, their resultant power is zero.

The $B$ molecule is framed on one side by liquid molecules, and on the other side by gas atoms, the final concentration of which is much lower than the combination of elementary particles of the liquid. Since much more molecules act on the $B$ molecule from the side of the liquid than from the side of an ideal gas, the resultant of all intermolecular forces can no longer be equated to zero, since this parameter is directed inside the volume of the substance. Thus, in order for a molecule from the depth of the liquid to end up in the surface layer, work must be performed against uncompensated forces. And 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 the 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 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).

This value directly depends on:

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

Remark 1

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

It is also known from mechanics that the minimum value of its internal energy always corresponds to the unchanged states of the system. Due to this physical process, the liquid body often takes on a shape with a minimal surface area. If the liquid is not affected by extraneous forces or their action is extremely small, its elements are in the form of a sphere in the form of a drop of water or a soap bubble. Similarly, water begins to behave in zero gravity. The fluid moves in such a way as if there are factors acting tangentially to its main surface that reduce this medium. These forces are called surface tension forces.

Therefore, the surface tension coefficient can also be defined as the basic modulus of the surface tension force, which generally acts per unit length of the initial contour that delimits the free fluid medium. The presence of these parameters makes the surface of a liquid substance look like a stretched elastic film, with the only difference that the constant 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 sinking.

The action of an external factor can describe 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. As a result, a surface tension force arises that tends to reduce such a change in area. The resultant force will always be directed exclusively upwards, compensating for the effect of gravity.

The result of surface tension

Under the influence of surface tension, small amounts of liquid media tend to take on a spherical shape that will ideally fit the smallest size of the environment. Approximation to a spherical configuration is achieved the more, the weaker the initial gravity forces, since for small drops the surface tension force index 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 forces 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, which involve changes in the height of the liquid level in the 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 vessels is determined.