Oscillations occurring under the influence of restoring force. The main property of oscillatory systems. The speed of sound depends on
Mechanical vibrations – these are movements that repeat exactly or approximately at regular intervals. (for example, swing of a branch on a tree, a pendulum of a clock, a car on springs, and so on)
Oscillations are free and forced.
Oscillations arising in the system under the action of internal forces are calledfree... All free vibrations are damped. (for example: string vibrations after impact)
Oscillations made by bodies under the action of external periodically changing forces are calledforced (for example: oscillation of a metal workpiece when a blacksmith is hammering).
Free vibration conditions :
- When the body is removed from the equilibrium position, a force must arise in the system that tends to return it to the equilibrium position;
- The friction forces in the system must be very small (i.e. tend to zero).
… E kin → E R → E kin →…
Using the example of body vibrations on a thread, we see energy conversion ... In position 1, we observe the balance of the oscillatory system. The speed and, therefore, the kinetic energy of the body is maximum. When the pendulum deviates from the equilibrium position, it rises to a height h relative to the zero level, therefore, at point A, the pendulum has potential energy E p ... When moving to the equilibrium position, to point O, the height decreases to zero, and the speed of the load increases, and at point O all potential energy E p will turn into kinetic energy E kin ... In the equilibrium position, kinetic energy is at its maximum and potential energy is at its minimum. After passing the equilibrium position by inertia, the kinetic energy is converted into potential energy, the speed of the pendulum decreases and at maximum
A movement in which the states of motion of the body are repeated over time, and the body passes through a position of stable equilibrium alternately in opposite directions, is called mechanical oscillatory motion.
If the states of movement of the body are repeated at regular intervals, then the oscillations are periodic. The physical system (body), in which, when deviating from the equilibrium position, oscillations arise and exist, is called an oscillatory system.
The oscillatory process in the system can occur under the influence of both external and internal forces.
Oscillations occurring in the system under the action of only internal forces are called free.
In order for free oscillations to arise in the system, it is necessary:
- The presence of a stable equilibrium position of the system. Thus, free oscillations will arise in the system shown in Figure 13.1, a; in cases b and c they will not arise.
- The presence of excess mechanical energy at a material point in comparison with its energy in a position of stable equilibrium. So, in the system (Fig. 13.1, a) it is necessary, for example, to bring the body out of the equilibrium position: i.e. communicate an excess of potential energy.
- The action on the material point of the restoring force, i.e. force always directed towards the equilibrium position. In the system shown in Fig. 13.1, a, the restoring force is the resultant force of gravity and the force of the normal reaction \ (\ vec N \) of the support.
- In ideal oscillatory systems, there are no friction forces, and the resulting oscillations can last for a long time. In real conditions, oscillations occur in the presence of resistance forces. In order for the oscillation to arise and continue, the excess energy received material point when shifting from a stable equilibrium position, it should not be completely spent on overcoming resistance when returning to this position.
Literature
Aksenovich L.A. Physics in high school: Theory. Tasks. Tests: Textbook. allowance for institutions providing the receipt of obs. environments, education. - S. 367-368.
General properties all oscillatory systems:
The presence of a position of stable equilibrium.
The presence of a force that returns the system to an equilibrium position.
Oscillatory motion characteristics:
Amplitude - the greatest (in modulus) deviation of the body from the equilibrium position.
Period - the period of time during which the body makes one complete vibration.
Frequency is the number of oscillations per unit of time.
Phase (phase difference)
Disturbances spreading in space, moving away from the place of their occurrence, are called waves.
A necessary condition for the appearance of a wave is the appearance at the moment of the appearance of a disturbance of forces that prevent it, for example, elastic forces.
Types of waves:
Longitudinal - a wave in which oscillations occur along the direction of wave propagation
Transverse - a wave in which oscillations occur perpendicular to the direction of their propagation.
Wave characteristics:
Wavelength is the distance between points closest to each other, oscillating in the same phases.
Wave speed is a value numerically equal to the distance that any point of the wave travels per unit time.
Sound waves - these are longitudinal elastic waves. The human ear perceives vibrations with a frequency from 20 Hz to 20,000 Hz in the form of sound.
The source of sound is a body vibrating at a sound frequency.
Sound receiver - a body capable of perceiving sound vibrations.
The speed of sound is the distance that a sound wave propagates in 1 second.
The speed of sound depends on:
Temperatures.
Sound characteristics:
Pitch
Amplitude
Volume. Depends on the vibration amplitude: the larger the vibration amplitude, the louder the sound.
Ticket number 9. Models of the structure of gases, liquids and solids. Thermal motion of atoms and molecules. Brownian motion and diffusion. Interaction of particles of matter
Gas molecules, moving in all directions, are almost not attracted to each other and fill the entire vessel. In gases, the distance between molecules is much greater than the size of the molecules themselves. Since, on average, the distances between molecules are tens of times larger than the size of molecules, they are weakly attracted to each other. Therefore, gases do not have their own form and constant volume.
The molecules of the liquid do not diverge over long distances, and the liquid under normal conditions retains its volume. Liquid molecules are located close to each other. The distance between every two molecules is less than the size of the molecules, so the attraction between them becomes significant.
In solids, the attraction between molecules (atoms) is even greater than that of liquids. Therefore, under normal conditions, solids retain their shape and volume. In solids, molecules (atoms) are arranged in a specific order. These are ice, salt, metals, etc. Such bodies are called crystals. Molecules or atoms of solids vibrate around a certain point and cannot travel far from it. A solid body therefore retains not only its volume, but also its shape.
Because its t is associated with the speed of movement of molecules, then the chaotic movement of the molecules that make up the bodies is called thermal motion... Thermal motion differs from mechanical motion in that many molecules participate in it and each moves randomly.
Brownian motion - This is a random movement of small particles suspended in a liquid or gas, occurring under the impact of environmental molecules. Discovered and first explored in 1827 by the English botanist R. Brown like the movement of pollen in water, seen at high magnification. Brownian motion does not stop.
The phenomenon in which there is a mutual penetration of molecules of one substance between the molecules of another is called diffusion.
Mutual attraction exists between the molecules of matter. At the same time, there is a repulsion between the molecules of a substance.
At distances comparable to the sizes of the molecules themselves, attraction is more noticeable, and with further approach, repulsion.
Ticket№ 10. Thermal equilibrium. Temperature. Temperature measurement. Relationship between temperature and the speed of chaotic movement of particles
Two systems are in a state of thermal equilibrium if, upon contact through a diathermic partition, the state parameters of both systems do not change. The diathermic baffle does not at all interfere with the thermal interaction of the systems. With thermal contact, the two systems come to a state of thermal equilibrium.
Temperature is a physical quantity that roughly characterizes the average kinetic energy of particles of a macroscopic system in a state of thermodynamic equilibrium per degree of freedom.
Temperature is a physical quantity that characterizes the degree of body heating.
Temperature is measured using thermometers. The main units of measure for temperature are Celsius, Fahrenheit and Kelvin.
Thermometer - a device used to measure the temperature of a given body by comparing it with reference values, conventionally selected as reference points and allowing you to set the measurement scale. In this case, different thermometers use different relationships between temperature and some observable property of the device, which can be considered linearly dependent on temperature.
As the temperature rises, the average particle velocity increases.
As the temperature decreases, the average particle velocity decreases.
Ticket number 11. Internal energy. Work and heat transfer as ways of changing the internal energy of the body. The law of conservation of energy in thermal processes
The energy of motion and interaction of the particles that make up the body is called internal energy of the body.
The internal energy of the body does not depend either on the mechanical movement of the body, or on the position of this body relative to other bodies.
The internal energy of the body can be changed in two ways: by performing mechanical work or by heat transfer.
heat transfer.
As the temperature rises, the body's internal energy increases. With a decrease in temperature, the internal energy of the body decreases. The internal energy of the body increases when doing work on it.
Mechanical and internal energy can transfer from one body to another.
This conclusion is valid for all thermal processes. With heat transfer, for example, a more heated body gives off energy, and a less heated body receives energy.
When energy is transferred from one body to another, or when one type of energy is converted into another, energy persists .
If heat exchange occurs between the bodies, then the internal energy of all heating bodies increases as much as the internal energy of cooling bodies decreases.
Ticket№ 12. Types of heat transfer: thermal conductivity, convection, radiation. Examples of heat transfer in nature and technology
The process of changing internal energy without doing work on the body or the body itself is called heat transfer.
The transfer of energy from more heated parts of the body to less heated ones as a result of thermal motion and interaction of particles is called thermal conductivity.
At convection energy is carried by the jets of gas or liquid themselves.
Radiation - the process of transferring heat by radiation.
Energy transfer by radiation differs from other types of heat transfer in that it can be carried out in a complete vacuum.
Examples of heat transfer in nature and technology:
The winds. All winds in the atmosphere are convection currents on a huge scale.
Convection explains, for example, winds and breezes that occur on the shores of the seas. On summer days, the land is warmed up by the sun faster than water, therefore the air over land heats up more than over water, its density decreases and the pressure becomes less than the pressure of colder air over the sea. As a result, as in communicating vessels, cold air moves down from the sea to the coast - the wind blows. This is the daytime breeze. At night, water cools more slowly than land, and air becomes colder over land than over water. A night breeze is formed - the movement of cold air from land to sea.
Traction. We know that fuel combustion is impossible without fresh air. If air does not enter the firebox, the stove, the samovar pipe, the fuel will stop burning. Usually they use a natural flow of air - draft. To create traction above the furnace, for example, in boiler plants of factories, plants, power plants, a pipe is installed. When the fuel burns, the air in it heats up. This means that the pressure of the air in the firebox and pipe becomes less than the pressure of the outside air. Due to the pressure difference, cold air enters the firebox, and warm air rises up - a draft is formed.
The higher the chimney built above the firebox, the greater the pressure difference between the outside air and the air in the chimney. Therefore, the thrust increases with increasing pipe height.
Heating and cooling of living quarters. Residents of countries located in the temperate and cold zones of the Earth are forced to heat their homes. In countries located in tropical and subtropical zones, the air temperature even in January reaches + 20 and +30 o C. Devices that cool the air in rooms are used here. Both heating and cooling of indoor air are based on convection.
It is advisable to place the cooling devices at the top, closer to the ceiling, so that natural convection takes place. After all, cold air has a greater density than warm air, and therefore will go down.
Heating devices are located at the bottom. Many modern large houses are equipped with hot water heating. The circulation of water in it and the heating of the air in the room occurs due to convection.
If the installation for heating the building is located in it, then a boiler is installed in the basement, in which the water is heated. Hot water rises along a vertical pipe from the boiler into a tank, which is usually placed in the attic of a house. A system of distribution pipes is carried out from the tank, through which water passes to radiators installed on all floors, it gives them its heat and returns to the boiler, where it is heated up again. This is the natural circulation of water - convection.
Oscillatory motion + §25, 26, Ex. 23.Fluctuations are a very common type of movement. You have probably seen oscillatory movements at least once in your life in a swinging pendulum of a clock or branches of trees in the wind. Chances are, you've at least once pulled the strings of your guitar and seen them vibrate. Obviously, even if you haven't seen with your own eyes, you can at least imagine how a needle moves in a sewing machine or a piston in an engine.
In all these cases, we have some kind of body that periodically performs repetitive movements. It is precisely these movements that are called in physics oscillations or oscillatory movements. Oscillations occur in our life very, very often.
Sound- these are fluctuations in the density and pressure of air,
radio waves- periodic changes in the strengths of the electric and magnetic fields,
visible light- also electromagnetic oscillations, only with slightly different wavelength and frequency.
Earthquakes- soil vibrations,
ebb and flow- change in the level of seas and oceans caused by the attraction of the moon and reaching 18 meters in some areas,
heartbeat- periodic contractions of the human heart muscle, etc.
The change of wakefulness and sleep, work and rest, winter and summer ... Even our daily going to work and returning home falls under the definition of fluctuations, which are interpreted as processes exactly or approximately repeating at regular intervals.
Oscillations are mechanical, electromagnetic, chemical, thermodynamic and various others. Despite such a variety, they all have much in common and therefore are described by the same equations.
home general characteristics periodically repeating movements - these movements are repeated at regular intervals, called a period of oscillation.
Let's summarize:mechanical vibrations Are body movements that repeat exactly or approximately at regular intervals.
A special branch of physics - the theory of oscillations - deals with the study of the laws of these phenomena. It is necessary to know them for shipbuilders and aircraft builders, industry and transport specialists, creators of radio engineering and acoustic equipment.
In the process of making vibrations, the body constantly strives to a position of equilibrium. Oscillations arise due to the fact that someone or something has rejected this body from its equilibrium position, thus giving the body energy, which determines its further oscillations.
Vibrations that occur only due to this original energy are called free vibrations. This means that they do not need constant help from the outside to maintain the oscillatory motion. 
Most of the fluctuations in the reality of life occur with gradual attenuation due to frictional forces, air resistance, and so on. Therefore, such oscillations are often called free oscillations, the gradual damping of which can be neglected during the observation period.
In this case, all bodies connected and directly participating in vibrations are collectively called an oscillatory system. In general, it is usually said that an oscillatory system is a system in which oscillations can exist.
In particular, if a freely suspended body oscillates on a thread, then the body itself, the suspension, will enter the oscillatory system, then to which the suspension and the Earth with its attraction are attached, which makes the body oscillate, constantly returning it to a state of rest. 
Such a body is a pendulum. In physics, several types of pendulums are distinguished: thread, spring and some others. All systems in which an oscillating body or its suspension can be conventionally represented as a thread are thread systems. If this ball is displaced away from the equilibrium position and released, then it will begin hesitate, that is, to perform repetitive movements, periodically passing through the equilibrium position.
Well, spring pendulums, as you might guess, consist of a body and a certain spring that can vibrate under the influence of the spring's elastic force.
The main model for observing oscillations is the so-called mathematical pendulum. A mathematical pendulum called a body of small size (compared to the length of the thread), suspended on a thin inextensible thread, the mass of which is negligible compared to the mass body. Simply put, in our reasoning we do not take into account the thread of the pendulum at all.
What properties should bodies have so that we can safely say that they constitute an oscillatory system, and we can describe it theoretically and mathematically.
Well, think for yourself how the oscillatory motion occurs for a thread pendulum.
As a hint - a picture.
