Propagation of vibrations in a medium. Longitudinal and transverse waves. Summary of the lesson "Propagation of oscillations in a medium. Waves. Characteristics of waves"

We present to your attention a video lesson on the topic “Propagation of vibrations in an elastic medium. Longitudinal and transverse waves. In this lesson, we will study issues related to the propagation of oscillations in an elastic medium. You will learn what a wave is, how it appears, how it is characterized. Let us study the properties and differences between longitudinal and transverse waves.

We turn to the study of issues related to waves. Let's talk about what a wave is, how it appears and what it is characterized by. It turns out that in addition to just an oscillatory process in a narrow region of space, it is also possible to propagate these oscillations in a medium, and it is precisely such propagation that is wave motion.

Let's move on to a discussion of this distribution. To discuss the possibility of the existence of oscillations in a medium, we must define what a dense medium is. A dense medium is a medium that consists of a large number particles whose interaction is very close to elastic. Imagine the following thought experiment.

Rice. 1. Thought experiment

Let us place a sphere in an elastic medium. The ball will shrink, decrease in size, and then expand like a heartbeat. What will be observed in this case? In this case, the particles that are adjacent to this ball will repeat its movement, i.e. move away, approach - thereby they will oscillate. Since these particles interact with other particles more distant from the ball, they will also oscillate, but with some delay. Particles that are close to this ball, oscillate. They will be transmitted to other particles, more distant. Thus, the oscillation will propagate in all directions. Note that in this case, the oscillation state will propagate. This propagation of the state of oscillations is what we call a wave. It can be said that the process of propagation of vibrations in an elastic medium over time is called a mechanical wave.

Please note: when we talk about the process of occurrence of such oscillations, we must say that they are possible only if there is an interaction between particles. In other words, a wave can exist only when there is an external perturbing force and forces that oppose the action of the perturbing force. In this case, these are elastic forces. The propagation process in this case will be related to the density and strength of interaction between the particles of this medium.

Let's note one more thing. The wave does not carry matter. After all, particles oscillate near the equilibrium position. But at the same time, the wave carries energy. This fact can be illustrated by tsunami waves. Matter is not carried by the wave, but the wave carries such energy that brings great disasters.

Let's talk about the types of waves. There are two types - longitudinal and transverse waves. What longitudinal waves? These waves can exist in all media. And the example with a pulsating ball inside a dense medium is just an example of the formation of a longitudinal wave. Such a wave is a propagation in space over time. This alternation of compaction and rarefaction is a longitudinal wave. I repeat once again that such a wave can exist in all media - liquid, solid, gaseous. Longitudinal is called a wave, during the propagation of which the particles of the medium oscillate along the direction of wave propagation.

Rice. 2. Longitudinal wave

As for the transverse wave, transverse wave can exist only in solids and on the surface of a liquid. A wave is called a transverse wave, during the propagation of which the particles of the medium oscillate perpendicular to the direction of wave propagation.

Rice. 3. Shear wave

The propagation speed of longitudinal and transverse waves is different, but this is the topic of the next lessons.

List of additional literature:

Are you familiar with the concept of a wave? // Quantum. - 1985. - No. 6. - S. 32-33. Physics: Mechanics. Grade 10: Proc. for in-depth study of physics / M.M. Balashov, A.I. Gomonova, A.B. Dolitsky and others; Ed. G.Ya. Myakishev. - M.: Bustard, 2002. Elementary textbook of physics. Ed. G.S. Landsberg. T. 3. - M., 1974.

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The process of propagation of vibrations in an elastic medium is called sound.

The process of propagation of oscillations in space is called a wave. The boundary separating oscillating particles from particles that have not yet begun to oscillate is called the water front. The propagation of a wave in a medium is characterized by a speed called the speed of an ultrasonic wave. The distance between the nearest particles oscillating in the same way (in the same phase) is called the wavelength. Number of waves passing through given point in 1 s is called the frequency of ultrasound.

The process of propagation of oscillations in an elastic medium is called wave motion, or an elastic wave.

The process of propagation of oscillations in space over time is called a wave. Waves propagating due to the elastic properties of the medium are called elastic. Elastic waves are transverse and longitudinal.

The process of vibration propagation in an elastic medium is called a wave. If the direction of oscillation coincides with the direction of wave propagation, then such a wave is called longitudinal, for example, a sound wave in air. If the direction of oscillation is perpendicular to the direction of wave propagation, then such a wave is called transverse.

The process of propagation of oscillations in space is called the wave process.

The process of propagation of oscillations in space is called a wave.

The process of vibration propagation in an elastic medium is called a wave. If the direction of oscillation coincides with the direction of wave propagation, then such a wave is called longitudinal, for example, a sound wave in air. If the direction of oscillation is perpendicular to the direction of wave propagation, then such a wave is called transverse.

The process of propagation of particle oscillations in an elastic medium is called a wave process or simply a wave.

The processes of propagation of fluctuations of liquid or gas particles in a pipe are complicated by the influence of its walls. Oblique reflections along the pipe walls create conditions for the formation of radial oscillations. Having set the task of studying axial vibrations of liquid or gas particles in narrow pipes, we must take into account a number of conditions under which radial vibrations can be neglected.

A wave is the process of propagation of oscillations in a medium. Each particle of the medium oscillates around the equilibrium position.

A wave is the process of propagation of vibrations.

The process of propagation of oscillations in an elastic medium considered by us is an example of wave motions, or, as they usually say, waves. So, for example, it turns out that electromagnetic waves (see § 3.1) can propagate not only in matter, but also in vacuum. The so-called gravitational waves (gravity waves) have the same property, with the help of which perturbations of the gravitational fields of bodies are transmitted, due to a change in the masses of these bodies or their positions in space. Therefore, in physics, waves are any perturbations of the state of matter or field propagating in space. So, for example, sound waves in gases or liquids are pressure fluctuations propagating in these media, and electromagnetic waves are fluctuations in the strengths E and H of the electromagnetic field propagating in space.

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Slides captions:

Lesson topic: Propagation of vibrations in elastic media. Waves

A dense medium is a medium that consists of a large number of particles whose interaction is very close to elastic.

The process of propagation of vibrations in an elastic medium over time is called a mechanical wave.

Conditions for the occurrence of a wave: 1. The presence of an elastic medium 2. The presence of a source of vibrations - deformation of the medium

Mechanical waves can propagate only in some medium (substance): in a gas, in a liquid, in a solid. A mechanical wave cannot arise in a vacuum.

Waves are generated by oscillating bodies that create a deformation of the medium in the surrounding space.

WAVES longitudinal transverse

Longitudinal - waves in which oscillations occur along the direction of propagation. Occur in any medium (liquids, gases, solid bodies).

Transverse - in which oscillations occur perpendicular to the direction of wave movement. Occur only in solids.

Waves on the surface of a liquid are neither longitudinal nor transverse. If you throw a small ball on the surface of the water, you can see that it moves, swaying on the waves, along a circular path.

Wave energy A traveling wave is a wave where energy is transferred without the transfer of matter.

Tsunami waves. Matter is not carried by the wave, but the wave carries such energy that brings great disasters.

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Let the oscillating body be in a medium, all particles of which are interconnected. The particles of the medium in contact with it will begin to oscillate, as a result of which periodic deformations (for example, compression and tension) occur in the areas of the medium adjacent to this body. During deformations, elastic forces appear in the medium, which tend to return the particles of the medium to their original state of equilibrium.

Thus, periodic deformations that have appeared in some place of the elastic medium will propagate at a certain speed, depending on the properties of the medium. In this case, the particles of the medium are not involved by the wave in translational motion, but perform oscillatory motions around their equilibrium positions, only elastic deformation is transmitted from one part of the medium to another.

The process of propagation of oscillatory motion in a medium is called wave process or just wave. Sometimes this wave is called elastic because it is caused by the elastic properties of the medium.

Depending on the direction of particle oscillations in relation to the direction of wave propagation, longitudinal and transverse waves are distinguished.Interactive demonstration of transverse and longitudinal waves

Longitudinal wave – it is a wave in which the particles of the medium oscillate along the direction of wave propagation.

Longitudinal wave can be observed on a long soft spring large diameter. By hitting one of the ends of the spring, one can notice how successive condensations and rarefaction of its coils will spread along the spring, running one after another. In the figure, the dots show the position of the coils of the spring at rest, and then the positions of the coils of the spring at successive intervals equal to a quarter of the period.

transverse wave - This is a wave in which the particles of the medium oscillate in directions perpendicular to the direction of wave propagation.

Let us consider in more detail the process of formation of transverse waves. Let us take as a model of a real cord a chain of balls (material points) connected to each other by elastic forces. The figure shows the process of propagation of a transverse wave and shows the positions of the balls at successive time intervals equal to a quarter of the period.

At the initial moment of time (t0 = 0) all points are in equilibrium. Then we cause a perturbation by deviating point 1 from the equilibrium position by the value A and the 1st point begins to oscillate, the 2nd point, elastically connected to the 1st, comes into oscillatory motion a little later, the 3rd - even later, etc. . After a quarter period of oscillation ( t 2 = T 4 ) spread to the 4th point, the 1st point will have time to deviate from its equilibrium position by a maximum distance equal to the amplitude of oscillations A. After half a period, the 1st point, moving down, will return to the equilibrium position, the 4th deviated from the equilibrium position by a distance equal to the amplitude of oscillations A, the wave propagated to the 7th point, etc.

By the time t5 = T The 1st point, having made a complete oscillation, passes through the equilibrium position, and the oscillatory movement will spread to the 13th point. All points from the 1st to the 13th are located so that they form a complete wave consisting of hollows and comb.

Demonstration of shear wave propagation

The type of wave depends on the type of deformation of the medium. Longitudinal waves due to compression deformation - tension, transverse waves - shear deformation. Therefore, in gases and liquids, in which elastic forces arise only during compression, the propagation of transverse waves is impossible. In solids, elastic forces arise both during compression (tension) and shear, therefore, the propagation of both longitudinal and transverse waves is possible in them.

As the figures show, in both transverse and longitudinal waves, each point of the medium oscillates around its equilibrium position and shifts from it by no more than an amplitude, and the state of deformation of the medium is transferred from one point of the medium to another. An important difference between elastic waves in a medium and any other ordered motion of its particles is that the propagation of waves is not associated with the transfer of matter in the medium.

waves are any perturbations of the state of matter or field, propagating in space over time.

Mechanical called waves that arise in elastic media, i.e. in media in which forces arise that prevent:

1) tensile (compression) deformations;

2) shear deformations.

In the first case, there longitudinal wave, in which the oscillations of the particles of the medium occur in the direction of propagation of the oscillations. Longitudinal waves can propagate in solid, liquid and gaseous bodies, because they are associated with the appearance of elastic forces when changing volume.

In the second case, there exists in space transverse wave, in which the particles of the medium oscillate in directions perpendicular to the direction of propagation of vibrations. Transverse waves can only propagate in solids, because associated with the emergence of elastic forces when changing forms body.

If a body oscillates in an elastic medium, then it acts on the particles of the medium adjacent to it, and makes them perform forced oscillations. The medium near the oscillating body is deformed, and elastic forces arise in it. These forces act on particles of the medium that are more and more distant from the body, taking them out of equilibrium. Everything over time large quantity particles of the medium is involved in oscillatory motion.

Mechanical wave phenomena are of great importance for Everyday life. For example, due to sound waves due to elasticity environment we can hear. These waves in gases or liquids are pressure fluctuations propagating in a given medium. As examples of mechanical waves, one can also cite: 1) waves on the water surface, where the connection of adjacent sections of the water surface is due not to elasticity, but to gravity and surface tension forces; 2) blast waves from shell explosions; 3) seismic waves - fluctuations in earth's crust propagating from the earthquake.

The difference between elastic waves and any other ordered motion of the particles of the medium is that the propagation of oscillations is not associated with the transfer of the substance of the medium from one place to another over long distances.

The locus of points to which oscillations reach a certain point in time is called front waves. The wave front is the surface that separates the part of space already involved in the wave process from the area in which oscillations have not yet arisen.

The locus of points oscillating in the same phase is called wave surface. The wave surface can be drawn through any point in the space covered by the wave process. Consequently, there are an infinite number of wave surfaces, while there is only one wave front at any moment of time, it moves all the time. The shape of the front can be different depending on the shape and dimensions of the oscillation source and the properties of the medium.

In the case of a homogeneous and isotropic medium, spherical waves propagate from a point source, i.e. the wave front in this case is a sphere. If the source of oscillations is a plane, then near it any section of the wave front differs little from a part of the plane, therefore waves with such a front are called plane waves.

Let us assume that during the time some section of the wave front has moved to . Value

is called the propagation speed of the wave front or phase speed waves at this location.

A line whose tangent at each point coincides with the direction of the wave at that point, i.e. with the direction of energy transfer is called beam. In a homogeneous isotropic medium, the beam is a straight line perpendicular to the wave front.

Oscillations from the source can be either harmonic or non-harmonic. Accordingly, waves run from the source monochromatic and non-monochromatic. A non-monochromatic wave (containing oscillations of different frequencies) can be decomposed into monochromatic waves (each of which contains oscillations of the same frequency). A monochromatic (sinusoidal) wave is an abstraction: such a wave must be infinitely extended in space and time.