According to this law, a process whose only result is the transfer of energy in the form of heat from a colder body to a hotter one is impossible without changes in the system itself and environment.
The second law of thermodynamics expresses the tendency of a system consisting of a large number of randomly moving particles to spontaneous transition from less probable states to more probable ones. Prohibits the creation of a perpetual motion machine of the second kind.
Equal volumes of ideal gases at the same temperature and pressure contain the same number of molecules.
The law was discovered in 1811 by the Italian physicist A. Avogadro (1776–1856).
The law of interaction of two currents flowing in conductors located at a small distance from each other states: parallel conductors with currents in one direction attract, and with currents in the opposite direction they repel.
The law was discovered in 1820 by A. M. Ampere.
The law of hydro and aerostatics: a body immersed in a liquid or gas is subject to a buoyant force directed vertically upwards, equal to the weight of the liquid or gas displaced by the body, and applied at the center of gravity of the immersed part of the body. FA = gV, where g is the density of the liquid or gas, V is the volume of the submerged part of the body.
Otherwise, the law can be formulated as follows: a body immersed in a liquid or gas loses as much in its weight as the liquid (or gas) displaced by it weighs. Then P = mg - FA.
The law was discovered by the ancient Greek scientist Archimedes in 212 BC. e. It is the basis of the theory of floating bodies.
One of the laws of an ideal gas: at a constant temperature, the product of the gas pressure and its volume is a constant value. Formula: pV = const. Describes an isothermal process. The law of universal gravitation, or Newton's law of gravity: all bodies are attracted to each other with a force that is directly proportional to the product of the masses of these bodies and inversely proportional to the square of the distance between them. According to this law, the elastic deformations of a solid body are directly proportional to the external influences causing them. Describes the thermal effect of electric current: the amount of heat released in the conductor when a direct current passes through it is directly proportional to the square of the current strength, the resistance of the conductor and the passage time. Discovered by Joule and Lenz independently in the 19th century. The basic law of electrostatics, which expresses the dependence of the interaction force of two fixed point charges on the distance between them: two fixed point charges interact with a force that is directly proportional to the product of the magnitudes of these charges and inversely proportional to the square of the distance between them and the permittivity of the medium in which the charges are located. The value is numerically equal to the force acting between two fixed point charges of 1 C each located in vacuum at a distance of 1 m from each other.
Coulomb's law is one of the experimental substantiations of electrodynamics. Opened in 1785
One of the basic laws of electric current: the strength of a direct electric current in a circuit section is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance. Valid for metallic conductors and electrolytes, the temperature of which is maintained constant. In the case of a complete circuit, it is formulated as follows: the strength of the direct electric current in the circuit is directly proportional to the emf of the current source and inversely proportional to the impedance of the electric circuit.

Opened in 1826 by G. S. Ohm.

Description

In order for a relationship to be called a physical law, it must satisfy the following requirements:

• empirical confirmation. A physical law is considered true if it is confirmed by repeated experiments.
• Versatility. The law must be fair to a large number objects. Ideally - for all objects in the universe.
• Sustainability. Physical laws do not change with time, although they can be recognized as approximations to more precise laws.

Physical laws are usually expressed as a short verbal statement or a compact mathematical formula:

Examples

Main article: List of physical laws

Some of the most famous physical laws are:

Laws-principles

Some physical laws are universal in nature and are definitions in their essence. Such laws are often called principles. These include, for example, Newton's second law (definition of force), the law of conservation of energy (definition of energy), the principle of least action (definition of action), etc.

Laws-consequences of symmetries

Part of the physical laws are simple consequences of certain symmetries that exist in the system. So, the conservation laws according to Noether's theorem are consequences of the symmetry of space and time. And the Pauli principle, for example, is a consequence of the identity of electrons (the antisymmetry of their wave function with respect to the permutation of particles).

Approximation of laws

All physical laws are a consequence of empirical observations and are true with the same accuracy with which experimental observations are true. This restriction does not allow us to claim that any of the laws is absolute. It is known that some of the laws are obviously not absolutely accurate, but are approximations to more accurate ones. So, Newton's laws are valid only for sufficiently massive bodies moving at speeds much less than the speed of light. More precise are the laws of quantum mechanics and special relativity. However, they, in turn, are approximations of more accurate equations of quantum field theory.

see also

Notes

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See what "Law (physics)" is in other dictionaries:

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Helen Czerski

Physicist, oceanographer, presenter of popular science programs on the BBC.

When it comes to physics, we present some formulas, something strange and incomprehensible, unnecessary to an ordinary person. We may have heard something about quantum mechanics and cosmology. But between these two poles is precisely everything that makes up our daily life: planets and sandwiches, clouds and volcanoes, bubbles and musical instruments. And they are all governed by a relatively small number of physical laws.

We can constantly observe these laws in action. Take, for example, two eggs - raw and boiled - and spin them, and then stop. The boiled egg will remain motionless, the raw one will begin to rotate again. This is because you only stopped the shell, and the liquid inside continues to rotate.

This is a clear demonstration of the law of conservation of angular momentum. Simplified, it can be formulated as follows: starting to rotate around a constant axis, the system will continue to rotate until something stops it. This is one of the fundamental laws of the universe.

It comes in handy not only when you need to distinguish a boiled egg from a raw one. It can also be used to explain how the Hubble Space Telescope, being without any support in space, aims the lens at a certain part of the sky. It just has spinning gyroscopes inside, which essentially behave the same as a raw egg. The telescope itself rotates around them and thus changes its position. It turns out that the law, which we can test in our kitchen, also explains the device of one of the most outstanding technologies of mankind.

Knowing the basic laws governing our daily life, we stop feeling helpless.

To understand how the world around us works, we must first understand its basics -. We have to understand that physics is not just weird scientists in laboratories or complicated formulas. It is right in front of us, available to everyone.

Where to start, you might think. Surely you noticed something strange or incomprehensible, but instead of thinking about it, you told yourself that you are an adult and you do not have time for this. Chersky advises not to dismiss such things, but to start with them.

If you don't want to wait for something interesting to happen, put raisins in your soda and see what happens. Watch spilled coffee dry up. Tap the spoon on the edge of the cup and listen for the sound. Finally, try dropping the sandwich so that it doesn't fall butter-side down.

Second law of thermodynamics

According to this law, the process, the only result of which is the transfer of energy in the form of heat from a colder body to a hotter one, is impossible without changes in the system itself and the environment. The second law of thermodynamics expresses the tendency of a system consisting of a large number of randomly moving particles to spontaneous transition from less probable states to more probable states. Prohibits the creation of a perpetual motion machine of the second kind.

Avogardo's Law
Equal volumes of ideal gases at the same temperature and pressure contain the same number of molecules. The law was discovered in 1811 by the Italian physicist A. Avogadro (1776–1856).

Ampère's law
The law of interaction of two currents flowing in conductors located at a small distance from each other states: parallel conductors with currents in one direction attract, and with currents in the opposite direction they repel. The law was discovered in 1820 by A. M. Ampère.

Law of Archimedes

The law of hydro- and aerostatics: on a body immersed in a liquid or gas, a buoyant force acts vertically upwards, equal to the weight of the liquid or gas displaced by the body, and applied at the center of gravity of the immersed part of the body. FA = gV, where g is the density of the liquid or gas, V is the volume of the submerged part of the body. Otherwise, the law can be formulated as follows: a body immersed in a liquid or gas loses as much in its weight as the liquid (or gas) displaced by it weighs. Then P = mg - FA. The law was discovered by the ancient Greek scientist Archimedes in 212 BC. e. It is the basis of the theory of floating bodies.

Law of gravity

The law of universal gravitation, or Newton's law of gravity: all bodies are attracted to each other with a force that is directly proportional to the product of the masses of these bodies and inversely proportional to the square of the distance between them.

Boyle's Law - Mariotte

One of the laws of an ideal gas: at a constant temperature, the product of the gas pressure and its volume is a constant value. Formula: pV = const. Describes an isothermal process.

Hooke's law
According to this law, the elastic deformations of a solid body are directly proportional to the external influences causing them.

Dalton's Law
One of the main gas laws: the pressure of a mixture of chemically non-interacting ideal gases is equal to the sum of the partial pressures of these gases. Opened in 1801 by J. Dalton.

Joule–Lenz law

Describes the thermal effect of electric current: the amount of heat released in the conductor when a direct current passes through it is directly proportional to the square of the current strength, the resistance of the conductor and the passage time. Discovered by Joule and Lenz independently in the 19th century.

Coulomb's law

The basic law of electrostatics, which expresses the dependence of the interaction force of two fixed point charges on the distance between them: two fixed point charges interact with a force that is directly proportional to the product of the magnitudes of these charges and inversely proportional to the square of the distance between them and the permittivity of the medium in which the charges are located. The value is numerically equal to the force acting between two fixed point charges of 1 C each located in vacuum at a distance of 1 m from each other. Coulomb's law is one of the experimental substantiations of electrodynamics. Opened in 1785.

Lenz's Law
According to this law, the induction current always has such a direction that its own magnetic flux compensates for changes in the external magnetic flux that caused this current. Lenz's law is a consequence of the law of conservation of energy. Established in 1833 by E. H. Lenz.

Ohm's law

One of the basic laws of electric current: the strength of a direct electric current in a circuit section is directly proportional to the voltage at the ends of this section and inversely proportional to its resistance. Valid for metallic conductors and electrolytes, the temperature of which is maintained constant. In the case of a complete circuit, it is formulated as follows: the strength of the direct electric current in the circuit is directly proportional to the emf of the current source and inversely proportional to the impedance of the electric circuit. Opened in 1826 by G. S. Ohm.

Wave reflection law

The incident beam, the reflected beam and the perpendicular raised to the point of incidence of the beam lie in the same plane, and the angle of incidence is equal to the angle of refraction. The law is valid for mirror reflection.

Pascal's Law
The basic law of hydrostatics: the pressure produced by external forces on the surface of a liquid or gas is transmitted equally in all directions.

Law of refraction of light

The incident beam, the refracted beam and the perpendicular raised to the point of incidence of the beam lie in the same plane, and for these two media the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant value, called the relative refractive index of the second medium relative to the first.

The law of rectilinear propagation of light

The law of geometric optics, which states that light travels in a straight line in a homogeneous medium. Explains, for example, the formation of shade and penumbra.

Law of conservation of charge
One of the fundamental laws of nature: the algebraic sum of electric charges of any electrically isolated system remains unchanged. In an electrically isolated system, the law of conservation of charge allows the appearance of new charged particles, but the total electric charge of the particles that have appeared must always be equal to zero.

Law of conservation of momentum
One of the basic laws of mechanics: the momentum of any closed system for all processes occurring in the system remains constant (conserved) and can only be redistributed between parts of the system as a result of their interaction.

Charles' law
One of the basic gas laws: the pressure of a given mass of ideal gas at constant volume is directly proportional to temperature.

Law of electromagnetic induction

Describes the phenomenon of the appearance of an electric field when a magnetic field changes (the phenomenon of electromagnetic induction): the electromotive force of induction is directly proportional to the rate of change of the magnetic flux. The coefficient of proportionality is determined by the system of units, the sign is determined by the Lenz rule. The law was discovered by M. Faraday.

The law of conservation and transformation of energy
The general law of nature: the energy of any closed system for all processes occurring in the system remains constant (conserved). Energy can only be converted from one form to another and redistributed between parts of the system. For an open system, an increase (decrease) in its energy is equal to a decrease (increase) in the energy of the bodies and physical fields interacting with it.

Newton's laws
Classical mechanics is based on Newton's 3 laws. Newton's first law (law of inertia): a material point is in a state of rectilinear and uniform motion or rest if no other bodies act on it or the action of these bodies is compensated. Newton's second law (basic law of dynamics): the acceleration received by a body is directly proportional to the resultant of all forces acting on the body, and inversely proportional to the mass of the body. Newton's third law: the actions of two bodies are always equal in magnitude and directed in opposite directions.

Faraday's laws
Faraday's first law: the mass of the substance released on the electrode during the passage of an electric current is directly proportional to the amount of electricity (charge) that has passed through the electrolyte (m = kq = kIt). Faraday's second law: the ratio of the masses of various substances undergoing chemical transformations on the electrodes when the same electric charges pass through the electrolyte is equal to the ratio of chemical equivalents. The laws were established in 1833–1834 by M. Faraday.

First law of thermodynamics
The first law of thermodynamics is the law of conservation of energy for a thermodynamic system: the amount of heat Q communicated to the system is spent on changing the internal energy of the system U and performing work A against external forces by the system. The formula Q \u003d U + A underlies the operation of heat engines.

Bohr's postulates

Bohr's first postulate: an atomic system is stable only in stationary states, which correspond to a discrete sequence of atomic energy values. Each change in this energy is associated with a complete transition of the atom from one stationary state to another. Bohr's second postulate: the absorption and emission of energy by an atom occurs according to the law according to which the radiation associated with the transition is monochromatic and has a frequency: h = Ei – Ek, where h is Planck's constant, and Ei and Ek are the energies of the atom in stationary states.

left hand rule
Determines the direction of the force that acts on a conductor with current in a magnetic field (or a moving charged particle). The rule says: if the left hand is positioned so that the outstretched fingers show the direction of the current (particle velocity), and the lines of force magnetic field(lines of magnetic induction) entered the palm, then the thumb set aside will indicate the direction of the force acting on the conductor (positive particle; in the case of a negative particle, the direction of the force is opposite).

Right hand rule
Determines the direction of the induction current in a conductor moving in a magnetic field: if the palm of the right hand is positioned so that it includes the lines of magnetic induction, and the bent thumb is directed along the movement of the conductor, then four outstretched fingers will show the direction of the induction current.

Huygens principle
Allows you to determine the position of the wave front at any time. According to the Huygens principle, all points through which the wave front passes at time t are sources of secondary spherical waves, and the desired position of the wave front at time t coincides with the surface that envelops all secondary waves. Huygens' principle explains the laws of reflection and refraction of light.

Huygens–Fresnel principle
According to this principle, at any point outside an arbitrary closed surface enclosing a point source of light, the light wave excited by this source can be represented as the result of interference of secondary waves emitted by all points of the specified closed surface. The principle allows solving the simplest problems of light diffraction.

The principle of relativity
In any inertial frame of reference, all physical (mechanical, electromagnetic, etc.) phenomena proceed in the same way under the same conditions. It is a generalization of Galileo's principle of relativity.

Galileo's principle of relativity

The mechanical principle of relativity, or the principle of classical mechanics: in any inertial frame of reference, all mechanical phenomena proceed in the same way under the same conditions.

Sound
Sound is called elastic waves that propagate in liquids, gases and solids and are perceived by the ear of humans and animals. A person has the ability to hear sounds with frequencies in the range of 16-20 kHz. Sound with frequencies up to 16 Hz is called infrasound; with frequencies of 2 104-109 Hz - ultrasound, and with frequencies of 109-1013 Hz - hypersound. The science that studies sounds is called acoustics.

Light
Light in the narrow sense of the term is called electromagnetic waves in the range of frequencies perceived by the human eye: 7.5 '1014–4.3 '1014 Hz. The wavelength varies from 760 nm (red light) to 380 nm (violet light).

Scientists from planet Earth use a ton of tools in an attempt to describe how nature works and in general. That they come to laws and theories. What is the difference? A scientific law can often be reduced to a mathematical statement, like E = mc²; this statement is based on empirical data and its truth, as a rule, is limited to a certain set of conditions. In the case of E = mc² - the speed of light in vacuum.

A scientific theory often seeks to synthesize a set of facts or observations of specific phenomena. And in general (but not always) there is a clear and verifiable statement about how nature functions. It is not at all necessary to reduce scientific theory to an equation, but it does represent something fundamental about the workings of nature.

Both laws and theories depend on the basic elements of the scientific method, such as making hypotheses, doing experiments, finding (or not finding) empirical evidence, and drawing conclusions. After all, scientists must be able to replicate results if the experiment is to become the basis for a generally accepted law or theory.

In this article, we'll look at ten scientific laws and theories that you can brush up on even if you don't use a scanning electron microscope that often, for example. Let's start with an explosion and end with uncertainty.

If it is worth knowing at least one scientific theory, then let it explain how the universe reached its current state (or did not reach it). Based on studies by Edwin Hubble, Georges Lemaitre, and Albert Einstein, the Big Bang theory postulates that the universe began 14 billion years ago with a massive expansion. At some point, the universe was enclosed in one point and encompassed all the matter of the current universe. This movement continues to this day, and the universe itself is constantly expanding.

The Big Bang theory gained widespread support in scientific circles after Arno Penzias and Robert Wilson discovered the cosmic microwave background in 1965. Using radio telescopes, two astronomers have detected cosmic noise, or static, that does not dissipate over time. In collaboration with Princeton researcher Robert Dicke, the pair of scientists confirmed Dicke's hypothesis that the original Big Bang left behind low-level radiation that can be found throughout the universe.

Hubble's Cosmic Expansion Law

Let's hold Edwin Hubble for a second. While the Great Depression was raging in the 1920s, Hubble was performing groundbreaking astronomical research. Not only did he prove that there were other galaxies besides the Milky Way, but he also found that these galaxies were rushing away from our own, a movement he called receding.

In order to quantify the speed of this galactic motion, Hubble proposed the law of cosmic expansion, aka Hubble's law. The equation looks like this: speed = H0 x distance. Velocity is the speed of the recession of galaxies; H0 is the Hubble constant, or a parameter that indicates the expansion rate of the universe; distance is the distance of one galaxy to the one with which the comparison is made.

The Hubble constant was calculated at different meanings for quite a long time, however, it is currently frozen at a point of 70 km/s per megaparsec. For us it is not so important. The important thing is that the law is a convenient way to measure the speed of a galaxy relative to our own. And more importantly, the law established that the Universe consists of many galaxies, the movement of which can be traced to the Big Bang.

Kepler's laws of planetary motion

For centuries, scientists have battled each other and religious leaders over the orbits of the planets, especially whether they revolve around the sun. In the 16th century, Copernicus put forward his controversial concept of the heliocentric solar system where the planets revolve around the sun instead of the earth. However, it was not until Johannes Kepler, who drew on the work of Tycho Brahe and other astronomers, that a clear scientific basis for planetary motion emerged.

Kepler's three laws of planetary motion, developed in the early 17th century, describe the movement of planets around the sun. The first law, sometimes called the law of orbits, states that the planets revolve around the Sun in an elliptical orbit. The second law, the law of areas, says that the line connecting the planet to the sun forms equal areas at regular intervals. In other words, if you measure the area created by a drawn line from the Earth from the Sun and track the movement of the Earth for 30 days, the area will be the same regardless of the position of the Earth relative to the origin.

The third law, the law of periods, allows you to establish a clear relationship between the orbital period of the planet and the distance to the Sun. Thanks to this law, we know that a planet that is relatively close to the Sun, like Venus, has a much shorter orbital period than distant planets like Neptune.

Universal law of gravity

This may be par for the course today, but more than 300 years ago, Sir Isaac Newton proposed a revolutionary idea: any two objects, regardless of their mass, exert a gravitational attraction on each other. This law is represented by an equation that many schoolchildren encounter in the senior grades of physics and mathematics.

F = G × [(m1m2)/r²]

F is the gravitational force between two objects, measured in newtons. M1 and M2 are the masses of the two objects, while r is the distance between them. G is the gravitational constant, currently calculated as 6.67384(80) 10 −11 or N m² kg −2 .

The advantage of the universal law of gravity is that it allows you to calculate the gravitational attraction between any two objects. This ability is extremely useful when scientists, for example, launch a satellite into orbit or determine the course of the moon.

Newton's laws

While we're on the subject of one of the greatest scientists ever to live on Earth, let's talk about Newton's other famous laws. His three laws of motion form an essential part of modern physics. And like many other laws of physics, they are elegant in their simplicity.

The first of the three laws states that an object in motion remains in motion unless it is acted upon by an external force. For a ball rolling on the floor, the external force could be friction between the ball and the floor, or a boy hitting the ball in the other direction.

The second law establishes a relationship between the mass of an object (m) and its acceleration (a) in the form of the equation F = m x a. F is a force measured in newtons. It is also a vector, meaning it has a directional component. Due to the acceleration, the ball that rolls on the floor has a special vector in the direction of its movement, and this is taken into account when calculating the force.

The third law is quite meaningful and should be familiar to you: for every action there is an equal and opposite reaction. That is, for every force applied to an object on the surface, the object is repelled with the same force.

Laws of thermodynamics

The British physicist and writer C.P. Snow once said that an unscientist who did not know the second law of thermodynamics was like a scientist who had never read Shakespeare. Snow's now famous statement emphasized the importance of thermodynamics and the need even for people far from science to know it.

Thermodynamics is the science of how energy works in a system, whether it be an engine or the Earth's core. It can be reduced to a few basic laws, which Snow outlined as follows:

• You cannot win.
• You will not avoid losses.
• You cannot exit the game.

Let's look into this a bit. What Snow meant by saying you can't win is that since matter and energy are conserved, you can't gain one without losing the other (that is, E=mc²). It also means that you need to supply heat to run the engine, but in the absence of a perfectly closed system, some heat will inevitably escape into the open world, leading to the second law.

The second law - losses are inevitable - means that due to increasing entropy, you cannot return to the previous energy state. Energy concentrated in one place will always tend to places of lower concentration.

Finally, the third law - you can't get out of the game - refers to the lowest theoretically possible temperature - minus 273.15 degrees Celsius. When the system reaches absolute zero, the movement of molecules stops, which means that entropy will reach its lowest value and there will not even be kinetic energy. But in the real world it is impossible to reach absolute zero - only very close to it.

Strength of Archimedes

After ancient greek Archimedes discovered his principle of buoyancy, he allegedly shouted "Eureka!" (Found!) and ran naked through Syracuse. So says the legend. The discovery was so important. Legend also says that Archimedes discovered the principle when he noticed that the water in the bathtub rises when a body is immersed in it.

According to Archimedes' principle of buoyancy, the force acting on a submerged or partially submerged object is equal to the mass of fluid that the object displaces. This principle is of paramount importance in density calculations, as well as in the design of submarines and other ocean-going vessels.

Evolution and natural selection

Now that we have established some of the basic concepts of how the universe began and how physical laws affect our daily lives, let's turn our attention to the human form and find out how we got to this point. According to most scientists, all life on Earth has a common ancestor. But in order to form such a huge difference between all living organisms, some of them had to turn into a separate species.

In a general sense, this differentiation has occurred in the process of evolution. Populations of organisms and their traits have gone through mechanisms such as mutations. Those with more survival traits, like brown frogs that camouflage themselves in swamps, were naturally selected for survival. This is where the term natural selection comes from.

You can multiply these two theories by many, many times, and actually Darwin did this in the 19th century. Evolution and natural selection explain the enormous diversity of life on Earth.

General theory of relativity

Albert Einstein's general theory of relativity was, and remains, a major discovery that forever changed our view of the universe. Einstein's main breakthrough was the statement that space and time are not absolute, and gravity is not just a force applied to an object or mass. Rather, gravity has to do with the fact that mass warps space and time itself (spacetime).

To make sense of this, imagine that you are driving across the Earth in a straight line in an easterly direction from, say, the northern hemisphere. After a while, if someone wants to accurately determine your location, you will be much south and east of your original position. This is because the earth is curved. To drive straight east, you need to take into account the shape of the Earth and drive at an angle slightly north. Compare a round ball and a sheet of paper.

Space is pretty much the same. For example, it will be obvious to the passengers of a rocket flying around the Earth that they are flying in a straight line in space. But in reality, the space-time around them is curving under the force of Earth's gravity, causing them to both move forward and stay in Earth's orbit.

Einstein's theory had a huge impact on the future of astrophysics and cosmology. She explained a small and unexpected anomaly in Mercury's orbit, showed how starlight bends, and laid the theoretical foundations for black holes.

Heisenberg uncertainty principle

Einstein's expansion of relativity taught us more about how the universe works and helped lay the groundwork for quantum physics, leading to a completely unexpected embarrassment of theoretical science. In 1927, the realization that all the laws of the universe are flexible in a certain context led to the startling discovery of the German scientist Werner Heisenberg.

By postulating his uncertainty principle, Heisenberg realized that it is impossible to know at the same time as high level exactly two properties of the particle. You can know the position of an electron with a high degree of accuracy, but not its momentum, and vice versa.

Later, Niels Bohr made a discovery that helped explain the Heisenberg principle. Bohr found that the electron has the qualities of both a particle and a wave. The concept became known as wave-particle duality and formed the basis of quantum physics. Therefore, when we measure the position of an electron, we define it as a particle at a certain point in space with an indefinite wavelength. When we measure the momentum, we consider the electron as a wave, which means we can know the amplitude of its length, but not the position.