It is natural and correct to be interested in the world around us and the patterns of its functioning and development. That is why it is reasonable to pay attention to natural sciences, for example, physics, which explains the very essence of the formation and development of the Universe. The basic physical laws are not difficult to understand. Schools introduce children to these principles at a very young age.
For many, this science begins with the textbook “Physics (7th grade)”. The basic concepts of thermodynamics are revealed to schoolchildren; they become familiar with the core of the main physical laws. But should knowledge be limited to school? What physical laws should every person know? This will be discussed later in the article.
Science physics
Many of the nuances of the science described are familiar to everyone from early childhood. This is due to the fact that, in essence, physics is one of the areas of natural science. It tells about the laws of nature, the action of which influences the life of everyone, and in many ways even ensures it, about the characteristics of matter, its structure and patterns of movement.
The term "physics" was first recorded by Aristotle in the fourth century BC. Initially, it was synonymous with the concept of “philosophy”. After all, both sciences had a single goal - to correctly explain all the mechanisms of the functioning of the Universe. But already in the sixteenth century, as a result of the scientific revolution, physics became independent.
General law
Some basic laws of physics are applied in various branches of science. In addition to them, there are those that are considered to be common to all of nature. This is about
It implies that the energy of each closed system during the occurrence of any phenomena in it is certainly conserved. Nevertheless, it is capable of transforming into another form and effectively changing its quantitative content in different parts of the named system. At the same time, in an open system, energy decreases provided that the energy of any bodies and fields that interact with it increases.
In addition to the above general principle, physics contains basic concepts, formulas, laws that are necessary for the interpretation of processes occurring in the surrounding world. Exploring them can be incredibly exciting. Therefore, this article will briefly discuss the basic laws of physics, but in order to understand them more deeply, it is important to pay full attention to them.
Mechanics
Many basic laws of physics are revealed to young scientists in grades 7-9 at school, where such a branch of science as mechanics is more fully studied. Its basic principles are described below.
- Galileo's law of relativity (also called the mechanical law of relativity, or the basis of classical mechanics). The essence of the principle is that under similar conditions, mechanical processes in any inertial reference frames are completely identical.
- Hooke's law. Its essence is that the greater the impact on an elastic body (spring, rod, console, beam) from the side, the greater its deformation.
Newton's laws (represent the basis of classical mechanics):
- The principle of inertia states that any body is capable of being at rest or moving uniformly and in a straight line only if no other bodies act on it in any way, or if they somehow compensate for the action of each other. To change the speed of movement, the body must be acted upon with some force, and, of course, the result of the influence of the same force on bodies of different sizes will also differ.
- The main principle of dynamics states that the greater the resultant of the forces that are currently acting on a given body, the greater the acceleration it receives. And, accordingly, the greater the body weight, the lower this indicator.
- Newton's third law states that any two bodies always interact with each other according to an identical pattern: their forces are of the same nature, are equivalent in magnitude and necessarily have the opposite direction along the straight line that connects these bodies.
- The principle of relativity states that all phenomena occurring under the same conditions in inertial reference systems occur in an absolutely identical way.
Thermodynamics
The school textbook, which reveals to students the basic laws (“Physics. Grade 7”), also introduces them to the basics of thermodynamics. We will briefly consider its principles below.
The laws of thermodynamics, which are basic in this branch of science, are of a general nature and are not related to the details of the structure of a particular substance at the atomic level. By the way, these principles are important not only for physics, but also for chemistry, biology, aerospace engineering, etc.
For example, in the named industry there is a rule that defies logical definition: in a closed system, the external conditions for which are unchanged, an equilibrium state is established over time. And the processes that continue in it invariably compensate each other.
Another rule of thermodynamics confirms the desire of a system, which consists of a colossal number of particles characterized by chaotic motion, to independently transition from states less probable for the system to more probable ones.
And the Gay-Lussac law (also called it) states that for a gas of a certain mass under conditions of stable pressure, the result of dividing its volume by the absolute temperature certainly becomes a constant value.
Another important rule of this industry is the first law of thermodynamics, which is also commonly called the principle of conservation and transformation of energy for a thermodynamic system. According to him, any amount of heat that was imparted to the system will be spent exclusively on the metamorphosis of its internal energy and its performance of work in relation to any acting external forces. It was this pattern that became the basis for the formation of the operation scheme of heat engines.
Another gas law is Charles' law. It states that the greater the pressure of a certain mass of an ideal gas while maintaining a constant volume, the greater its temperature.
Electricity
The 10th grade of school reveals interesting basic laws of physics to young scientists. At this time, the main principles of the nature and patterns of action of electric current, as well as other nuances, are studied.
Ampere's law, for example, states that conductors connected in parallel, through which current flows in the same direction, inevitably attract, and in the case of the opposite direction of current, they repel, respectively. Sometimes the same name is used for a physical law that determines the force acting in an existing magnetic field on a small section of a conductor that is currently conducting current. That's what they call it - the Ampere force. This discovery was made by a scientist in the first half of the nineteenth century (namely in 1820).
The law of conservation of charge is one of the basic principles of nature. It states that the algebraic sum of all electric charges arising in any electrically isolated system is always conserved (becomes constant). Despite this, this principle does not exclude the emergence of new charged particles in such systems as a result of certain processes. Nevertheless, the total electric charge of all newly formed particles must certainly be equal to zero.
Coulomb's law is one of the main ones in electrostatics. It expresses the principle of the interaction force between stationary point charges and explains the quantitative calculation of the distance between them. Coulomb's law makes it possible to substantiate the basic principles of electrodynamics experimentally. It states that stationary point charges certainly interact with each other with a force, which is higher, the greater the product of their magnitudes and, accordingly, the smaller, the smaller the square of the distance between the charges in question and the medium in which the described interaction occurs.
Ohm's law is one of the basic principles of electricity. It states that the greater the strength of the direct electric current acting on a certain section of the circuit, the greater the voltage at its ends.
They call it a principle that allows you to determine the direction in a conductor of a current moving in a certain way under the influence of a magnetic field. To do this, you need to position your right hand so that the lines of magnetic induction figuratively touch the open palm, and extend your thumb in the direction of movement of the conductor. In this case, the remaining four straightened fingers will determine the direction of movement of the induction current.
This principle also helps to find out the exact location of the magnetic induction lines of a straight conductor conducting current at a given moment. It happens like this: place the thumb of your right hand so that it points and figuratively grasp the conductor with the other four fingers. The location of these fingers will demonstrate the exact direction of the magnetic induction lines.
The principle of electromagnetic induction is a pattern that explains the process of operation of transformers, generators, and electric motors. This law is as follows: in a closed loop, the greater the induction generated, the greater the rate of change of the magnetic flux.
Optics
The Optics branch also reflects part of the school curriculum (basic laws of physics: grades 7-9). Therefore, these principles are not as difficult to understand as they might seem at first glance. Their study brings with it not just additional knowledge, but a better understanding of the surrounding reality. The basic laws of physics that can be attributed to the study of optics are the following:
- Guynes principle. It is a method that can effectively determine the exact position of the wave front at any given fraction of a second. Its essence is as follows: all points that are in the path of the wave front in a certain fraction of a second, in essence, themselves become sources of spherical waves (secondary), while the location of the wave front in the same fraction of a second is identical to the surface , which goes around all spherical waves (secondary). This principle is used to explain existing laws related to the refraction of light and its reflection.
- The Huygens-Fresnel principle reflects an effective method for resolving issues related to wave propagation. It helps explain elementary problems associated with the diffraction of light.
- waves It is equally used for reflection in a mirror. Its essence is that both the incident beam and the one that was reflected, as well as the perpendicular constructed from the point of incidence of the beam, are located in a single plane. It is also important to remember that the angle at which the beam falls is always absolutely equal to the angle of refraction.
- The principle of light refraction. This is a change in the trajectory of an electromagnetic wave (light) at the moment of movement from one homogeneous medium to another, which differs significantly from the first in a number of refractive indices. The speed of light propagation in them is different.
- Law of rectilinear propagation of light. At its core, it is a law related to the field of geometric optics, and is as follows: in any homogeneous medium (regardless of its nature), light propagates strictly rectilinearly, over the shortest distance. This law explains the formation of shadows in a simple and accessible way.
Atomic and nuclear physics
The basic laws of quantum physics, as well as the fundamentals of atomic and nuclear physics, are studied in high school and higher education institutions.
Thus, Bohr's postulates represent a series of basic hypotheses that became the basis of the theory. Its essence is that any atomic system can remain stable only in stationary states. Any emission or absorption of energy by an atom necessarily occurs using the principle, the essence of which is as follows: radiation associated with transportation becomes monochromatic.
These postulates relate to the standard school curriculum studying the basic laws of physics (grade 11). Their knowledge is mandatory for a graduate.
Basic laws of physics that a person should know
Some physical principles, although they belong to one of the branches of this science, are nevertheless of a general nature and should be known to everyone. Let us list the basic laws of physics that a person should know:
- Archimedes' law (applies to the areas of hydro- and aerostatics). It implies that any body that has been immersed in a gaseous substance or liquid is subject to a kind of buoyant force, which is necessarily directed vertically upward. This force is always numerically equal to the weight of the liquid or gas displaced by the body.
- Another formulation of this law is as follows: a body immersed in a gas or liquid certainly loses as much weight as the mass of the liquid or gas in which it was immersed. This law became the basic postulate of the theory of floating bodies.
- The law of universal gravitation (discovered by Newton). Its essence is that absolutely all bodies are inevitably attracted to each other with a force, which is greater, the greater the product of the masses of these bodies and, accordingly, the less, the smaller the square of the distance between them.
These are the 3 basic laws of physics that everyone who wants to understand the functioning mechanism of the surrounding world and the peculiarities of the processes occurring in it should know. It is quite simple to understand the principle of their operation.
The value of such knowledge
The basic laws of physics must be in a person’s knowledge base, regardless of his age and type of activity. They reflect the mechanism of existence of all of today's reality, and, in essence, are the only constant in a continuously changing world.
Basic laws and concepts of physics open up new opportunities for studying the world around us. Their knowledge helps to understand the mechanism of existence of the Universe and the movement of all cosmic bodies. It turns us not into mere observers of daily events and processes, but allows us to be aware of them. When a person clearly understands the basic laws of physics, that is, all the processes occurring around him, he gets the opportunity to control them in the most effective way, making discoveries and thereby making his life more comfortable.
Results
Some are forced to study in depth the basic laws of physics for the Unified State Exam, others due to their occupation, and some out of scientific curiosity. Regardless of the goals of studying this science, the benefits of the knowledge gained can hardly be overestimated. There is nothing more satisfying than understanding the basic mechanisms and patterns of existence of the world around us.
Don't remain indifferent - develop!
“Questions on Physics” - What is the name of the device that converts sound vibrations into electrical vibrations? Question No. 12. Question No. 10. R. Mayer, who discovered the law of conservation of energy, was a doctor. Question No. 1. Major works in the field of solid state physics and general physics. Question No. 3. Question No. 7. Question No. 4. Question No. 2. The law of electrolysis is named after the English physicist Michael Faraday.
“Studying Physics” - So why do you need physics? Structure of matter. Physics is one of the many natural sciences. What does PHYSICS study? Optics. Thermodynamics and molecular physics. Electrodynamics. Mechanics! Physical phenomena: You also encounter electromagnetic phenomena at every step. Introductory lesson in physics, grade 7.
"Science of Physics" - Astronomy. Physical phenomena are changes in nature. The connections of physics are so diverse that sometimes people do not see them. Philosophy. Physical phenomena. Physics is one of the sciences about nature. Field. Mechanical phenomena. Physics as a science. General physical concepts. Sound phenomena. Water molecule. Mechanical phenomena are the movements of airplanes, cars, pendulums.
"Light Physics" - Earth's Orbit. Stages of development of ideas about the nature of light. “How many speeds does light have?” Development of views on the nature of light. What is light? Orbit of the moon Io. The duality of the properties of light is called corpuscular-wave dualism. Michelson's method: Light travel time t=2?/s, therefore gives c = 3.14 10 8 m/s.
“Unified State Examination in Physics 2010” - Changes in KIM 2010 compared to KIM 2009. Exam work plan. Distribution of exam paper tasks by difficulty level. Distribution of tasks by difficulty level. A system for evaluating the results of individual tasks and work as a whole. Changes have been made: the presentation form for assignment B1 has been updated, and the criteria for assessing assignments with a detailed answer have been updated.
“What physics studies” - Mechanical phenomena of nature. Atomic phenomena of nature. Clouds. Introducing students to a new school subject. Teacher's lecture "From the history of physics." Morning dew. Magnetic phenomena of nature. Solar eclipse. Natural phenomena. Optical phenomena of nature. What does physics study? Aristotle introduced the concept of “physics” (from the Greek word “fusis” - nature).
Determine the characteristics of motion used in theoretical mechanics that you know from your physics course:
1. straight motion
2. curvilinear movement
3. high-speed traffic
4. relative motion
5. jet propulsion
6. rail traffic
Option 8.
Task No. 1. Expand the following concepts: 1. Types of body deformations. Stiffness coefficient 2. Determination of mechanical work. 3. Sound waves. Conditions necessary for the emergence and existence of sound.
Task No. 2. Expand the following concept: Inertial frame of reference.
Task No. 3.
Determine on what special property of any body, in accordance with the laws of classical mechanics of I. Newton, the acceleration that this body receives when it interacts with another body depends.
1. From its speed
2. From his inertia
3. From its temperature
4. From its elasticity
Option 9.
Task No. 1. Expand the following concepts: 1. The concept of impulse. Law of conservation of momentum. 2. Power. Definition and physical formula. 3. Basic concepts of the theory of mechanical waves: Wavelength.
Task No. 2. Expand the following concept: Newton's first law is the law of inertial systems.
Task No. 3.
Total mechanical energy, i.e. the sum of the potential and kinetic energy of a body remains constant under certain physical conditions. At what?
1. An elastic force acts on the body
2. The force of gravity acts on the body
3. The body is not affected by friction force (it is absent)
4. The body is not affected by gravity
5. The sliding force acts on the body
6. The force of stubbornness acts on the body.
Option 10.
Task No. 1. Expand the following concepts: 1. Jet motion. Tsiolkovsky formula for determining the maximum speed of a rocket. 2. Kinetic energy. Physical formula of kinetic energy. 3. Basic concepts of the theory of mechanical waves. Wave beam.
Task No. 2. Expand the following concept: The principle of superposition of forces in the theory of I. Newton.
Task No. 3.
This physical quantity (or unit) measures electrical potential, potential difference, electrical voltage and electromotive force.
In this case, the potential difference between two points is equal to 1 volt, if in order to move a charge of the same magnitude from one point to another, work of the same magnitude (in absolute value) must be done on it.
In what units is the energy released when performing such work measured?
1. 1 Joule
5. 1 Newton
6. 1 Einstein
Written Assignment No. 4 (based on the results of December)
Option 1.
Task No. 1. Expand the following concepts: 1. The discoveries of Coulomb and Galvani.
2. Electromagnetic induction. 3. Second law of thermodynamics.
Task No. 2. Expand the following concept: Distinctive features of solids, liquids and gases.
Mechanical movement. In grade VIII, the mechanical form of the movement of matter was studied in detail, i.e., the movement in space of some bodies relative to others over time. The fact that all bodies are composed of atoms or molecules was not taken into account. Bodies were considered solid, devoid of internal structure.
The study of the properties of bodies is not the task of mechanics. Its goal is to determine the positions of bodies in space and their velocities at any time, depending on the forces of interaction between them at given initial positions and velocities of the bodies.
Thermal movement. Atoms and molecules of matter, as you know from the VII class physics course, undergo random (chaotic) motion, called thermal motion. In the section “Thermal phenomena. Molecular Physics" in class IX we will study the basic laws of the thermal form of motion of matter.
The movement of molecules is random due to the fact that their number in the bodies that surround us is immensely large and the molecules interact with each other. The concept of thermal motion does not apply to systems of several molecules. The chaotic movement of a huge number of molecules is qualitatively different from the ordered mechanical movement of individual bodies. That is why it represents a special form of movement of matter, which has specific properties.
Thermal motion determines the internal properties of bodies, and its study allows us to understand many physical processes occurring in bodies.
Macroscopic bodies. In physics, bodies consisting of a very large number of atoms or molecules are called macroscopic. The dimensions of macroscopic bodies are many times greater than the dimensions of atoms. Gas in a cylinder, water in a glass, a grain of sand, a stone, a steel rod, a globe - all these are examples of macroscopic bodies (Fig. 1).
We will consider processes in macroscopic bodies.
Thermal phenomena. The thermal movement of molecules depends on temperature. This was discussed in physics courses of grades VI and VII. Therefore, by studying the thermal motion of molecules, we will thereby study phenomena that depend on the temperature of bodies. When heated, transitions of matter occur from one
states into another: solids turn into liquids and liquids into gases. When cooling, on the contrary, gases turn into liquids, and liquids into solids.
These and many other phenomena caused by the chaotic movement of atoms and molecules are called thermal phenomena.
The significance of thermal phenomena. Thermal phenomena play a huge role in the lives of people, animals and plants. A change in air temperature by 20-30°C with the change of season changes everything around us. With the onset of spring, nature awakens, forests become covered with leaves, meadows turn green. In winter, the rich summer colors are replaced by a monotonous white background, the life of plants and many insects freezes. When our body temperature changes by just one degree, we already feel unwell.
Thermal phenomena have interested people since ancient times. People achieved relative independence from environmental conditions after they learned to make and maintain fire. This was one of the greatest discoveries made by man.
Temperature changes affect all properties of bodies. Thus, when heated or cooled, the size of solids and the volume of liquids change. Their mechanical properties, such as elasticity, also change significantly. A piece of rubber tubing will not be damaged if you hit it with a hammer. But when cooled to temperatures below -100°C, rubber becomes as fragile as glass. A slight impact breaks the rubber tube into small pieces. Only after heating the rubber will regain its elastic properties.
All of the above and many other thermal phenomena are subject to certain laws. These laws are as accurate and reliable as the laws of mechanics, but differ from them in content and form. The discovery of the laws that govern thermal phenomena makes it possible to apply these phenomena in practice and in technology with maximum benefit. Modern heat engines, installations for liquefying gases, refrigeration devices and other devices are designed based on knowledge of these laws.
Molecular kinetic theory. The theory that explains thermal phenomena in macroscopic bodies and the internal properties of these bodies based on the idea that all bodies consist of individual chaotically moving particles is called molecular kinetic theory. The theory sets the task of connecting the patterns of behavior of individual molecules with quantities characterizing the properties of macroscopic bodies.
Even ancient philosophers guessed that heat is a type of internal movement of particles that make up bodies. A great contribution to the development of molecular kinetic theory was made by the great Russian scientist M.V. Lomonosov. Lomonosov considered heat as the rotational movement of particles of matter. With the help of his theory, he gave a completely correct, in general terms, explanation of the phenomena of melting, evaporation and thermal conductivity. He concluded that there is a “greatest or last degree of cold,” when the movement of particles of matter stops
However, the difficulties of constructing a molecular kinetic theory led to its final victory only at the beginning of the 20th century. The fact is that the number of molecules in macroscopic bodies is enormous and it is impossible to trace the movement of each molecule. It is necessary to learn, based on the laws of motion of individual molecules, to find the average result to which their combined motion leads. It is this average result of the movement of all molecules that determines thermal phenomena in macroscopic bodies.
Thermodynamics. The substance has many properties that can be studied without delving into its structure. Thermal phenomena can be described using quantities recorded by instruments such as a pressure gauge and thermometer, which do not respond to the influence of individual molecules.
In the middle of the 19th century. After the discovery of the law of conservation of energy, the first scientific theory of thermal processes was constructed - thermodynamics. Thermodynamics is a theory of thermal phenomena that does not take into account the molecular structure of bodies. It arose while studying the optimal conditions for using heat to perform work long before the molecular kinetic theory received general recognition.
Thermodynamics and statistical mechanics. Currently, both thermodynamics and molecular kinetic theory, also called statistical mechanics, are used in science and technology. These theories complement each other.
The entire content of thermodynamics lies in several statements called the laws of thermodynamics. These laws have been established empirically. They are valid for all substances, regardless of their internal structure. Statistical mechanics is a deeper, but also more complex theory of thermal phenomena. With its help, all laws of thermodynamics can be theoretically substantiated.
First, we will dwell on the basic principles of molecular kinetic theory, known to us partly from the physics course of grades VI and VII. Then we will get acquainted with the quantitative molecular kinetic theory of the simplest system - a gas of relatively low density.
Physics exam papers for the 2006-2007 academic year. year
9th grade
Ticket No. 1. Mechanical movementtion. Path. Speed, Acceleration
Mechanical movement-- change in the position of a body in space relative to other bodies over time.
Path-- the length of the trajectory along which a body moves for some time. It is symbolized by the letter s and measured in meters (m). Calculated using the formula
Speed is a vector quantity equal to the ratio of the path to the time during which this path is covered. Determines both the speed of movement and its direction at a given time. It is designated by a letter and measured in meters per second (). Calculated using the formula
Acceleration with uniformly accelerated motion-- this is a vector quantity equal to the ratio of the change in speed to the period of time during which this change occurred. Determines the rate of change in speed in magnitude and direction. Denoted by the letter a or and is measured in meters per second squared (). Calculated using the formula
Ticket number 2. The phenomenon of inertia. Newton's first law. Strength and layerthe flow of strength. Newton's second law
The phenomenon of maintaining the speed of a body in the absence of the action of other bodies is called inertia.
Newton's first law: There are such reference systems relative to which bodies retain their speed unchanged if they are not acted upon by other bodies.
Frames of reference where the law of inertia is satisfied are called inert.
Frames of reference where the law of inertia does not hold - non-inert.
Force-- vector quantity. And it is a measure of the interaction of bodies. Denoted by the letter F or and is measured in newtons (N)
A force that produces the same effect on a body as several simultaneously acting forces is called resultant of these forces.
The resultant of forces directed along one straight line in one direction is directed in the same direction, and its modulus is equal to the sum of the moduli of the component forces.
The resultant of forces directed along one straight line in opposite directions is directed towards the force that is larger in magnitude, and its module is equal to the difference in the modules of the component forces.
The greater the resultant of the forces applied to the body, the greater the acceleration the body will receive.
When the force is halved, the acceleration also decreases by half, i.e.
Means, the acceleration with which a body of constant mass moves is directly proportional to the force applied to this body, as a result of which acceleration occurs.
When the body weight doubles, the acceleration decreases by half, i.e.
Means, the acceleration with which a body moves with a constant force is inversely proportional to the mass of that body.
The quantitative relationship between body mass, acceleration, and the resultant forces applied to the body is called Newton's second law.
Newton's second law: the acceleration of a body is directly proportional to the resultant forces applied to the body and inversely proportional to its mass.
Mathematically, Newton's second law is expressed by the formula:
Ticket number 3. Newton's third law. Pulse. Law of conservation of momentum. Explanation of reactive movements on OSnew law of conservation of momentum
Newton's third law: the forces with which two bodies act on each other are equal in magnitude and opposite in direction.
Mathematically, Newton's third law is expressed as follows:
Body impulse-- a vector quantity equal to the product of a body's mass and its speed. It is designated by a letter and measured in kilograms per second (). Calculated using the formula
law of conservation of momentum: sum of impulses of bodies before interaction is equal to the amount after interaction. Let's consider jet propulsion based on the movement of a balloon with a stream of air coming out of it. According to the law of conservation of momentum, the total momentum of a system consisting of two bodies must remain the same as it was before the outflow of air, i.e. equal to zero. Therefore, the ball begins to move in the direction opposite to the air stream at the same speed that its momentum is equal to the modulus of the air stream's momentum.
Ticket number 4. Gravity. Free fall. Acceleration of gravity. The law is universalwow it's a dragtenia
Gravity- the force with which the Earth attracts a body towards itself. Denoted by or
Free fall- movement of bodies under the influence of gravity.
In a given place on the Earth, all bodies, regardless of their masses and other physical characteristics, freely fall with the same acceleration. This acceleration is called acceleration of free fall and is denoted by the letter or. It
The law of universal gravitation: any two bodies attract each other with a force directly proportional to the mass of each of them and inversely proportional to the square of the distance between them.
G = 6.67?10 -11 N?m 2 /kg 2
G - Gravitational constant
Ticket number 5. Elastic force. Explanation of the device and operating principle of the dynamometer. Friction force. Friction in nature and technology
The force that arises in a body as a result of its deformation and tends to return the body to its original position is called elastic force. Indicated. Found by the formula
Dynamometer-- a device for measuring force.
The main part of the dynamometer is a steel spring, which is given different shapes depending on the purpose of the device. The simplest dynamometer is based on comparing any force with the elastic force of a spring.
When one body comes into contact with another, an interaction occurs that prevents their relative motion, which is called friction. And the force characterizing this interaction is called friction force. There is static friction, sliding friction and rolling friction.
Without static friction, neither people nor animals could walk on the ground, because... When we walk, we push off the ground with our feet. Without friction, objects would slip out of your hands. The force of friction stops a car when braking, but without static friction it would not be able to start moving. In many cases, friction is harmful and must be dealt with. To reduce friction, the contacting surfaces are made smooth, and a lubricant is introduced between them. To reduce friction of rotating shafts of machines and machine tools, they are supported by bearings.
Ticket No. 6. Pressure. Atmosphere pressure. Pascal's law. Archimedes' Law
The quantity equal to the ratio of the force acting perpendicular to the surface to the area of this surface is called pressure. It is denoted by the letter or and measured in pascals (Pa). Calculated using the formula
Atmosphere pressure-- this is the pressure of the entire thickness of air on the earth's surface and the bodies located on it.
Atmospheric pressure equal to the pressure of a column of mercury 760 mm high at temperature is called normal atmospheric pressure.
Normal atmospheric pressure is 101300 Pa = 1013 hPa.
Every 12m the pressure decreases by 1mm. Hg Art. (or by 1.33 hPa)
Pascal's law: the pressure exerted on a liquid or gas is transmitted to any point equally in all directions.
Archimedes' law: a body immersed in a liquid (or gas, or plasma) is subject to a buoyant force (called the Archimedes force)
where c is the density of the liquid (gas), is the acceleration of gravity, and V is the volume of the submerged body (or the part of the volume of the body located below the surface). The buoyant force (also called the Archimedean force) is equal in magnitude (and opposite in direction) to the force of gravity acting on the volume of liquid (gas) displaced by the body, and is applied to the center of gravity of this volume.
It should be noted that the body must be completely surrounded by liquid (or intersected by the surface of the liquid). So, for example, Archimedes' law cannot be applied to a cube that lies at the bottom of a tank, hermetically touching the bottom.
Ticket No. 7. Work of force. Kinetic and potential energy. Mechanical conservation law energy
Mechanical work is done only when a force acts on a body and it moves.
Mechanical work directly proportional to the force applied and directly proportional to the distance traveled. Symbolized by the letter or and measured in joules (J). Calculated using the formula
Energy -- a physical quantity that shows how much work a body can do. Energy is measured in joules (J).
Potential energy is called energy, which is determined by the relative position of interacting bodies or parts of the same body. Indicated by the letter or. Calculated using the formula
The energy possessed by a body due to its motion is called kinetic energy. Indicated by the letter or. Calculated using the formula
Law of conservation of mechanical energy:
In the absence of forces such as friction, mechanical energy does not arise from nothing and cannot disappear anywhere.
Ticket number 8. Mechanical vibrations. Mechanical waves. Sound. Fluctuations in nature and technology
A movement that is repeated after a certain period of time is called oscillatory.
Oscillations that occur only due to the initial supply of energy are called free vibrations.
A system of bodies that are capable of free vibrations is called oscillatory systems.
General properties of all oscillatory systems:
1. The presence of a stable equilibrium position.
2. The presence of a force that returns the system to an equilibrium position.
Characteristics of oscillatory motion:
1. Amplitude is the largest (in absolute value) deviation of the body from the equilibrium position.
2. Period - the period of time during which the body makes one complete oscillation.
3. Frequency - the number of oscillations per unit time.
4. Phase (phase difference)
Disturbances propagating in space, moving away from the place of their origin, are called waves.
A necessary condition for the occurrence of a wave is the appearance at the moment of the disturbance of forces preventing it, for example elastic forces.
Types of waves:
1. Longitudinal - a wave in which oscillations occur along the direction of propagation of the wave
2. Transverse - a wave in which vibrations occur perpendicular to the direction of their propagation.
Wave Characteristics:
1. Wavelength is the distance between points closest to each other, oscillating in the same phases.
2. Wave speed is a quantity numerically equal to the distance that any point on 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.
A sound receiver is a body capable of perceiving sound vibrations.
The speed of sound is the distance a sound wave travels in 1 second.
The speed of sound depends on:
2. Temperatures.
Sound characteristics:
1. Frequency
2. Pitch
3. Amplitude
4. Volume. Depends on the amplitude of the vibrations: the greater the amplitude of the vibrations, the louder the sound.
Ticket No. 9. Models of the structure of gases, liquids and solids. Thermal movement 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 container. 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 greater than the size of the molecules, they are weakly attracted to each other. Therefore, gases do not have their own shape and constant volume.
Liquid molecules do not disperse over long distances, and liquid under normal conditions retains its volume. The molecules of a liquid are located close to each other. The distances between each two molecules are smaller than the size of the molecules, so the attraction between them becomes significant.
In solids, the attraction between molecules (atoms) is even greater than in liquids. Therefore, under normal conditions, solids retain their shape and volume. In solids, molecules (atoms) are arranged in a certain order. These are ice, salt, metals, etc. Such bodies are called crystals. Molecules or atoms of solids vibrate around a certain point and cannot move far from it. Therefore, a solid body retains not only its volume, but also its shape.
Because t is associated with the speed of movement of molecules, then the chaotic movement of the molecules that make up bodies is called thermal movement. Thermal motion differs from mechanical motion in that it involves many molecules and each one moves randomly.
Brownian motion- this is the random movement of small particles suspended in a liquid or gas, occurring under the influence of impacts from environmental molecules. It was discovered and first studied in 1827 by the English botanist R. Brown as the movement of flower pollen in water, visible under high magnification. Brownian motion does not stop.
The phenomenon in which mutual penetration of molecules of one substance between the molecules of another occurs is called diffusion.
There is mutual attraction between the molecules of a substance. At the same time, there is repulsion between the molecules of the substance.
At distances comparable to the size of the molecules themselves, attraction becomes more noticeable, and with further approach, repulsion becomes more noticeable.
Ticket № 10 . Thermal equilibrium. Temperature. Temperature measurement. Relationship between temperature and speedyu chaotic particle movement
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 partition does not at all interfere with the thermal interaction of the systems. When thermal contact occurs, the two systems reach a state of thermal equilibrium.
Temperature is a physical quantity that approximately characterizes the average kinetic energy of particles of a macroscopic system per one degree of freedom that is in a state of thermodynamic equilibrium.
Temperature is a physical quantity that characterizes the degree of heating of a body.
Temperature is measured using thermometers. The basic units of temperature are Celsius, Fahrenheit and Kelvin.
Thermometer is a device used to measure the temperature of a given body by comparison with reference values, conditionally selected as reference points and allowing the measurement scale to be established. Moreover, 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 increases, the average speed of particle movement increases.
As the temperature decreases, the average speed of particle movement decreases.
Ticket No. 11. Internal energy. Work and heat transfer as ways to change internal energy bodies. The law has been preservedenergy in thermal processes
The energy of movement and interaction of particles that make up a body is called internal energy of the body.
The internal energy of a body does not depend either on the mechanical motion of the body or on the position of this body relative to other bodies.
The internal energy of a body can be changed in two ways: by performing mechanical work or by heat transfer.
heat transfer.
As the temperature rises, the internal energy of the body increases. As the temperature decreases, the internal energy of the body decreases. The internal energy of a body increases when work is done on it.
Mechanical and internal energy can move from one body to another.
This conclusion is valid for all thermal processes. During heat transfer, for example, a more heated body gives off energy, and a less heated body receives energy.
When energy passes from one body to another or when one type of energy is converted into another, energy is conserved .
If heat exchange occurs between 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 movement and interaction of particles is called thermal conductivity.
At convection energy is transferred by the gas or liquid jets 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:
1. Winds. All winds in the atmosphere are convection currents of enormous scale.
Convection explains, for example, wind breezes that arise on the shores of the seas. On summer days, land is heated by the sun faster than water, therefore the air above land heats up more than above water, its density decreases and the pressure becomes less than the pressure of colder air above the sea. As a result, as in communicating vessels, cold air from the sea below moves to the shore - the wind blows. This is the daytime breeze. At night, water cools more slowly than land, and the air above land becomes colder than above water. A night breeze is formed - the movement of cold air from land to sea.
2. Traction. We know that without a supply of fresh air, combustion of fuel is impossible. If no air enters the firebox, the oven, or the pipe of the samovar, the combustion of the fuel will stop. Usually they use natural air flow - draft. To create draft above the firebox, for example, in boiler installations of factories, plants, power plants, a pipe is installed. When fuel burns, the air in it heats up. This means that the air pressure 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 upward - a draft is formed.
The higher the pipe built above the firebox, the greater the difference in pressure between the outside air and the air in the pipe. Therefore, the thrust increases with increasing pipe height.
3. Residential heating and cooling. Residents of countries located in 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. Here they use devices that cool the air in rooms. Both heating and cooling of indoor air are based on convection.
It is advisable to place cooling devices at the top, closer to the ceiling, so that natural convection occurs. After all, cold air has a greater density than warm air, and therefore will sink.
Heating devices are located below. Many modern large houses have water heating. The circulation of water in it and the heating of the air in the room occur due to convection.
If the installation for heating the building is located in the building itself, then a boiler is installed in the basement in which water is heated. A vertical pipe extending from the boiler carries hot water into a tank, which is usually placed in the attic of the house. From the tank, a system of distribution pipes is carried out, through which water passes into radiators installed on all floors, it gives off its heat to them and returns to the boiler, where it is heated again. This is how the natural circulation of water occurs - convection.
Larger buildings use more complex installations. Hot water is supplied to several buildings at once from a boiler installed in a special room. Water is driven into. buildings using pumps, i.e. create artificial convection.
4. Heat transfer and flora. The temperature of the lower layer of air and the surface layer of soil is of great importance for the development of plants.
Temperature changes occur in the layer of air adjacent to the Earth and the upper layer of soil. During the day, the soil absorbs energy and heats up; at night, on the contrary, it cools. Its heating and cooling is influenced by the presence of vegetation. Thus, dark, plowed soil is heated more strongly by radiation, but cools faster than soil covered with vegetation.
The heat exchange between soil and air is also affected by the weather. On clear, cloudless nights, the soil cools greatly - radiation from the soil easily goes into space. On such nights in early spring, frosts on the soil are possible. If the weather is cloudy, then the clouds cover the Earth and play the role of original screens that protect the soil from energy loss through radiation.
One of the means of increasing the temperature of an area of soil and ground air is greenhouses, which make it possible to more fully use the radiation of the Sun. The soil area is covered with glass frames or transparent films. Glass transmits visible solar radiation well, which, when it hits dark soil, heats it, but it transmits invisible radiation emitted by the heated surface of the Earth less well. In addition, glass (or film) prevents the upward movement of warm air, i.e., convection. Thus, greenhouse glass acts as an energy “trap”. The temperature inside greenhouses is approximately 10 °C higher than on unprotected soil.
5. Thermos. Heat transfer from a hotter body to a colder one leads to equalization of their temperatures. Therefore, if you bring, for example, a hot kettle into the room, it will cool down. Part of its internal energy will transfer to surrounding bodies. To prevent the body from cooling down or heating up, you need to reduce heat transfer. At the same time, they strive to ensure that energy is not transferred by any of the three types of heat transfer: convection, thermal conductivity and radiation.
It consists of a glass vessel with double walls. The inner surface of the walls is covered with a shiny metal layer, and air is pumped out from the space between the walls of the vessel. The airless space between the walls does not conduct heat; the shiny layer, due to reflection, prevents the transfer of energy by radiation. To protect the glass from damage, the thermos is placed in a cardboard or metal case. The vessel is sealed with a stopper, and a cap is screwed on top of the case.
Ticket number 13. Quantity of heat. Specific heat capacityawn. Melting. Crystallization
The energy that a body gains or loses during heat transfer is called amount of heat. Symbolized by the letter Q and measured in joules (J). Calculated using the formula
The amount of heat required to heat a body (or released by it when cooling) depends on the type of substance from which it consists, on the mass of this body and on the change in its temperature.
To calculate the amount of heat required to heat a body or released by it during cooling, the specific heat capacity of the substance must be multiplied by the mass of the body and by the difference between its higher and lower temperatures.
A physical quantity that shows how much heat is required to change the temperature of a substance weighing 1 kg by 1°C is called specific heat capacity. Identified by a letter and measured in. Calculated using the formula
The specific heat capacity of some substances,
The transition of a substance from solid to liquid is called melting.
The temperature at which a substance melts is called the melting point of the substance.
The transition of a substance from a liquid to a solid state is called solidification or crystallization.
The temperature at which a substance hardens (crystallizes) is called the solidification or crystallization temperature.
Substances solidify at the same temperature at which they melt.
Melting point of some substances, °C
A physical quantity showing how much heat must be imparted to a crystalline body weighing 1 kg in order to completely transform it into a liquid state at the melting point is called specific heat of fusion. Identified by a letter and measured in. Calculated using the formula
Specific heat of fusion of certain substances (at melting point)
Ticket No. 14 . Evaporation. Condensation. Boiling. Air humidity
The phenomenon of turning a liquid into vapor is called vaporization.
There are two ways for a liquid to change into a gaseous state evaporation And boiling.
Vaporization occurring from the surface of a liquid is called evaporation.
The rate of evaporation depends on the type of liquid. Evaporation must occur at any temperature. Evaporation occurs faster the higher the temperature of the liquid. The rate of evaporation of a liquid depends on its surface area. When there is wind, liquid evaporates faster.
The phenomenon of vapor turning into liquid is called condensation.
Boiling is an intense transition of liquid into vapor due to the formation and growth of vapor bubbles, which at a certain temperature for each liquid float to its surface and burst.
The temperature at which a liquid boils is called the boiling point. During boiling, the temperature of the liquid does not change.
The boiling point of some substances, °C
A physical quantity showing how much heat is needed to convert a liquid weighing 1 kg into steam without changing temperature is called specific heat of vaporization. Identified by a letter and measured in. Calculated using the formula
Specific heat of vaporization of certain substances (at boiling point)
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Ammonia (liquid) |
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Ticket No. 15. Electrification of bodies. Two types of electric charges. Interaction of charges. The law is preservedelectric charge
A body which, after being rubbed, attracts other bodies to itself, is said to be electrified or what to him electrical charge is imparted.
Bodies made of different substances can become electrified. Electrification of bodies occurs upon contact and subsequent separation of bodies.
Two bodies are involved in electrification. In this case, both bodies are electrified.
There are two types of electric charges.
The charge obtained on glass rubbed against silk was called positive, those. attributed to the "+" sign. And the charge obtained on amber rubbed on wool was called negative, those. attributed the sign "-".
Bodies having electric charges of the same sign repulse, and bodies having electric charges of the opposite sign, mutually are attracted.
Law of conservation of electric charge: the algebraic sum of electric charges in a closed system remains constant.
Ticket number 16. Constant electric current. Electrical circuit. Electrical resistance. Law Ohm for an electrical circuit section
Electric shock called the ordered movement of charged particles. Electric current has a certain direction. The direction of current is taken to be the direction of movement of positively charged particles.
An electrical circuit is a collection of various devices and the conductors connecting them (or elements of an electrically conductive medium) through which electric current can flow.
Electrical resistance is the reciprocal of electrical conductivity. Measured in Ohms.
1 ohm is the resistance of a conductor in which, at a voltage at the ends of 1 volt, the current strength is 1 ampere.
Ohm's law for a section of a circuit: The current strength in a section of the circuit is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance.
Ticket № 17 . Work and power of electric current. Law Joule- Lenza. Use of thermal action of current in technology
The work of an electric current on a section of a circuit is equal to the product of the voltage at the ends of this section by the current strength and the time during which the work was performed.
Work is measured in joules (J) or watts per second (W?s).
The power of the electric current is equal to the product of voltage and current.
Power is measured in watts (W).
Joule-Lenz law: the amount of heat generated by a current-carrying conductor is equal to the product of the square of the current, the resistance of the conductor and time.
Using the thermal effect of current in technology:
The main part of a modern incandescent lamp is a spiral of thin tungsten wire. Tungsten is a refractory metal, its melting point is 3,387 °C. In an incandescent lamp, the tungsten filament is heated to 3,000°C, at which temperature it reaches white heat and glows with bright light. The spiral is placed in a glass flask, from which air is pumped out with a pump so that the spiral does not burn out. But in a vacuum, tungsten quickly evaporates, the spiral becomes thinner and also burns out relatively quickly. To prevent the rapid evaporation of tungsten, modern lamps are filled with nitrogen, sometimes with inert gases - krypton or argon. Gas molecules prevent tungsten particles from leaving the filament, i.e., they prevent the destruction of the heated filament.
The thermal effect of current is used in various electric heating devices and installations. At home, electric stoves, irons, kettles, and boilers are widely used. In industry, the thermal effect of current is used for smelting special grades of steel and many other metals, for electric welding. In agriculture, electric current is used to heat greenhouses, feed steamers, incubators, dry grain, and prepare silage.
The main part of any heating electrical device is a heating element. The heating element is a conductor with high resistivity, which is also capable of withstanding heating to high temperatures without destruction. Most often, an alloy of nickel, iron, chromium and manganese, known as nichrome, is used to make the heating element.
In the heating element, a conductor in the form of a wire or tape is wound on a plate made of heat-resistant material: mica, ceramic. For example, the heating element in an electric iron is a nichrome strip, which heats the lower part of the iron.
Ticket № 18 . Electric field. Action of an electric field on electric charges. Capacitor. Energy eelectric field of a capacitor
An electric field is a special form of matter that exists regardless of our ideas about it.
The main property of the electric field is its effect on electric charges with some force.
The electric field of stationary charges is called electrostatic. It doesn't change over time. An electrostatic field is created only by electric charges. It exists in the space surrounding these charges and is inextricably linked with them.
Capacitor consists of two conductors separated by a dielectric layer, the thickness of which is small compared to the size of the conductors.
The conductors in this case are called capacitor plates .
The energy of a capacitor is proportional to its electrical capacity and the square of the voltage between the plates. All this energy is concentrated in the electric field. The field energy density is proportional to the square of the field strength.
Ticket number 19. Oersted's experience. Magnetic field of current. Interaction of magnets. The action of magneticto a current-carrying conductor
Oersted's experience:
Let's place a conductor connected to the current source circuit above the magnetic needle parallel to its axis. When the circuit is closed, the magnetic needle deviates from its original position. When the circuit is opened, the magnetic needle returns to its original position. This means that the current-carrying conductor and the magnetic needle interact with each other.
The experiment performed suggests the existence of a conductor with electric current around magnetic field. It acts on the magnetic needle, deflecting it.
A magnetic field exists around any current-carrying conductor, that is, around moving electric charges. Electric current and magnetic field are inseparable from each other.
The lines along which the axes of small magnetic needles are located in a magnetic field are called magnetic field lines. The direction indicated by the north pole of the magnetic needle at each point in the field is taken to be the direction of the magnetic field line.
Magnetic current magnetic field lines are closed curves surrounding a conductor.
Bodies that retain magnetization for a long time are called permanent magnets or simply magnets.
Those places in the magnet where the strongest magnetic effects are found are called magnet poles. Every magnet, like the magnetic needle we know, necessarily has two poles: northern (N) And southern (S).
By bringing a magnet close to the poles of a magnetic needle, you will notice that the north pole of the needle is repelled by the north pole of the magnet and attracted to the south pole. The south pole of the needle is repelled by the south pole of the magnet and attracted by the north pole.
Based on the described experiments, the following conclusion can be drawn: Opposite magnetic poles attract, like magnetic poles repel. This rule also applies to electromagnets.
The interaction of magnets is explained by the fact that there is a magnetic field around any magnet. The magnetic field of one magnet acts on another magnet, and, conversely, the magnetic field of the second magnet acts on the first.
A magnetic field acts with some force on any current-carrying conductor located in this field.
Ticket No. 20. The phenomenon of electromagnetic induction. Induction current. Faraday's experiments. Variable current
The phenomenon of electromagnetic induction consists in the occurrence of an electric current in a closed circuit when the magnetic flux changes through the surface limited by this circuit.
The electric current arising from the phenomenon of electromagnetic induction is called induction.
Faraday's experiments:
An electric current that periodically changes with time in magnitude and direction is called variables.
Ticket number 21. Law of rectilinear propagation of light. Law of light reflection. Flat mirror. The phenomenon ofbreaking light
Law of rectilinear propagation of light: Light propagates in a straight line in a transparent medium.
Laws of light reflection: 1. The incident and reflected rays lie in the same plane with a perpendicular drawn to the interface between the two media at the point of incidence of the ray. 2. The angle of incidence is equal to the angle of reflection.
A mirror whose surface is a plane is called a plane mirror.
The image of an object in a flat mirror has the following features: this image is virtual, direct, equal in size to the object, and it is located at the same distance behind the mirror as the object is located in front of the mirror.
Light refraction-- the phenomenon of changing the direction of propagation of light when it passes through the interface between two speeds.
Ticket No. 22. Lens. Focal length of the lens. Constructing an image in a converging lens. Eye like an optical system
Lenses can be convex or concave.
Let us first consider the properties of a convex lens.
Let's fix the lens in the optical disk and direct a beam of rays parallel to its optical axis at it (Fig. 150). We will see that the rays are refracted twice - when passing from air into the lens and when leaving it into the air. As a result of this, they will change their direction and intersect at one point lying on the optical axis of the lens; this point is called lens focus F. The distance from the optical center of the lens to this point is called focal length of the lens; it is also denoted by the letter F.
A convex lens is called a converging lens.
A concave lens is called diverging lens. But a concave (divergent) lens has a focus, only it imaginary. If the diverging beam of rays emerging from such a lens is continued in the direction opposite to their direction, then the extensions of the rays will intersect at point F , lying on the optical axis on the same side from which the light falls on the lens. This point is called imaginary focus of a diverging lens
If an object is located between the lens and its focus, then its image is enlarged, virtual, direct, and it is located on the same side of the lens as the object, and further than the object.
If an object is between the focus and the double focus of a lens, then the lens gives an enlarged, inverted, real image of it; it is located on the other side of the lens in relation to the subject, behind double the focal length.
If an object is behind the double focus of the lens, then the lens gives a reduced, inverted, real image of the object lying on the other side of the lens between its focus and the double focus
The human eye is almost spherical and is protected by a dense membrane called sclera. Anterior part of the sclera -- cornea transparent Located behind the cornea Iris, which may have different colors for different people. Between the cornea and the iris is watery liquid.
There is a hole in the iris - pupil, the diameter of which, depending on the lighting, can vary from approximately 2 to 8 mm. It changes because the iris is able to move apart.
Behind the pupil there is a transparent body, similar in shape to a converging lens - this lens, he is surrounded muscles, attaching it to the sclera.
Located behind the lens vitreous body. It is transparent and fills the rest of the eye. The back of the sclera -- the fundus of the eye -- is covered mesh shell. The retina consists of the finest fibers that cover the fundus of the eye like villi. They are branched endings optic nerve, sensitive to light.
Light falling into the eye is refracted on the front surface of the eye, in the cornea, lens and vitreous body, due to which a real, reduced, inverted image of the objects in question is formed on the retina.
Light falling on the endings of the optic nerve, which make up the retina, irritates these endings. Irritations are transmitted along nerve fibers to the brain, and a person receives a visual impression and sees objects. The vision process is corrected.........