To understand whether it is worth continuing to write short sketches that literally explain different physical phenomena and processes. The result dispelled my doubts. I will continue. But in order to approach rather complex phenomena, you will have to make separate consecutive series of posts. So, in order to get to the story about the structure and evolution of the Sun and other types of stars, one will have to start with a description of the types of interaction between elementary particles. Let's start with this. Without formulas.
In total, four types of interaction are known in physics. All well known gravitational and electromagnetic. And almost unknown to the general public strong and weak. Let's describe them sequentially.
Gravitational interaction . Man has known him since ancient times. For it is constantly in the field of gravity of the Earth. And from school physics we know that the force of gravitational interaction between bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. Under the influence of gravitational force, the Moon revolves around the Earth, the Earth and other planets around the Sun, and the latter, together with other stars, around the center of our Galaxy.
The rather slow decrease in the strength of the gravitational interaction with distance (inversely proportional to the square of the distance) leads physicists to speak of this interaction as long-range. In addition, the forces of gravitational interaction acting between bodies are only forces of attraction.
Electromagnetic interaction . In the simplest case of electrostatic interaction, as we know from school physics, the force of attraction or repulsion between electrically charged particles is proportional to the product of their electrical charges and inversely proportional to the square of the distance between them. Which is very similar to the law of gravitational interaction. The only difference is that electric charges those with the same sign repel, and those with different signs attract. Therefore, the electromagnetic interaction, like the gravitational one, is called by physicists long-range.
At the same time, the electromagnetic interaction is more complicated than the gravitational one. From school physics, we know that an electric field is created by electric charges, magnetic charges do not exist in nature, and a magnetic field is created electric currents.
In fact, the electric field can also be created by changing in time magnetic field, and the magnetic field - time-varying electric field. The latter circumstance makes it possible to exist electromagnetic field no electrical charges or currents at all. And this possibility is realized in the form electromagnetic waves. For example, radio waves and light quanta.
Because of the similar distance dependence of the electric and gravitational forces, it is natural to try to compare their intensities. So, for two protons, the forces of gravitational attraction turn out to be 10 to the 36th power (a billion billion billion billion times) weaker than the forces of electrostatic repulsion. Therefore, in the physics of the microcosm, the gravitational interaction can be quite reasonably neglected.
Strong interaction . This is - short range strength. In the sense that they operate at distances of only the order of one femtometer (one trillionth of a millimeter), and at long distances their influence is practically not felt. Moreover, at distances of the order of one femtometer, the strong interaction is about a hundred times more intense than the electromagnetic one.
That is why equally electrically charged protons in the atomic nucleus do not repel each other by electrostatic forces, but are held together by a strong interaction. Because the size of the proton and neutron is about one femtometer.
Weak interaction . It is really very weak. First, it operates at distances a thousand times smaller than one femtometer. And at long distances it is practically not felt. Therefore, like the strong one, it belongs to the class short-range. Secondly, its intensity is about a hundred billion times less than the intensity of the electromagnetic interaction. The weak force is responsible for some of the decays elementary particles. including free neutrons.
There is only one type of particles that interact with matter only through the weak interaction. This is a neutrino. Almost a hundred billion solar neutrinos pass through every square centimeter of our skin every second. And we don't notice them at all. In the sense that during our lifetime it is unlikely that a few pieces of neutrino will interact with the matter of our body.
We will not talk about theories describing all these types of interactions. For a qualitative picture of the world is important for us, and not the sophistication of theoreticians.

Force- a measure of the mechanical interaction of bodies. Force is the cause of a change in the speed of a body or the occurrence of deformations in it (a change in shape or volume). Force is a vector quantity characterized by its modulus (magnitude), direction and point of application of the force. The line of action of the force is a straight line passing through the point of application of the force and continuing the direction of the force vector. The SI unit of force is Newton [N]. All forces in nature are based on four types of fundamental interactions:

• electromagnetic forces acting between electrically charged bodies,
• gravitational forces acting between massive objects,
• strong nuclear force, acting on scales of the order of the size of an atomic nucleus and less (responsible for the connection between quarks in hadrons and for the attraction between nucleons in nuclei).
• weak nuclear interaction, which manifests itself at distances much smaller than the size of the atomic nucleus.

The intensity of the strong and weak interactions is measured in units of energy (electron volts), and not in units of force, and therefore the application of the term "force" to them is arbitrary. The action of force can take place both in direct contact (friction, pressure on each other in direct contact), and through the fields created by the bodies (gravitational field, electromagnetic field). An interesting and informative site http://mistermigell.ru for you.
From the point of view of the action of forces on the system, consider:

• internal forces - forces of interaction between points (bodies) of a given system;
• external forces - forces acting on points (bodies) of a given system from points (bodies) that do not belong to this system. External forces are called loads.

Forces can be divided into:

• reactive forces − coupling reactions. If the movement of a body in space is limited by other bodies (bonds, supports), the forces with which these bodies act on a given body are called connection (support) reactions.
• active forces - forces that characterize the action of other bodies on a given one and change its kinematic state. Active forces, depending on the type of contact, are divided into
• volumetric - forces acting on each particle of the body, for example, the weight of the body;
• surface - forces acting on a part of the body and characterizing the direct contact of the bodies. Surface forces are:
• concentrated - acting on sites that are small compared to the body, for example, the pressure of a wheel on the road;
• distributed - acting on sites that are not small compared to the body, for example, the pressure of a tractor caterpillar on the road.

The most famous forces:
elastic forces- the forces arising from the deformation of the body and opposing this deformation, is of an electromagnetic nature, being a manifestation of intermolecular interaction. The elastic force vector is directed opposite to the displacement, perpendicular to the surface. For example, if you compress an elastic band, after removing the load, it will restore its shape under the action of an elastic force.
Friction forces− force arising from relative motion of solid bodies and counteracting this movement, are of an electromagnetic nature, being a macroscopic manifestation of intermolecular interaction. The friction force vector is directed opposite to the velocity vector. For example, the force of friction occurs when a sled slides on snow, between the soles of the feet and the ground.
Environmental resistance forces- the forces arising from the motion of a solid body in a liquid or gaseous medium are of an electromagnetic nature, being a manifestation of intermolecular interaction. The resistance force vector is directed opposite to the velocity vector. For example, when an aircraft is moving in the air.
Surface tension forces− the forces arising on the surface of the phase separation are electromagnetic in nature, being a manifestation of intermolecular interaction. The tension force is directed tangentially to the interface. For example, a coin can lie on the surface of a liquid, insects run on water.
Force gravity - the force with which any bodies of the Universe attract each other, it is directly proportional to the product of the masses of these bodies and inversely proportional to the square of the distance between them. For example, the Earth is attracted to the Sun, and, at the same time, the Earth is attracted to the Moon and the Sun.
Gravity is the force acting on the body from the side of the Earth, which imparts to it the acceleration of free fall. Gravity is the sum of the forces of gravitational attraction and the centrifugal force of the Earth's rotation. For example, under the influence of gravity of a body, the Earth falls.
inertia force− fictitious force (not a measure of mechanical interaction) introduced when considering relative motion in non-inertial frames of reference (moving with acceleration) in order to fulfill Newton's second law in them. In the frame of reference associated with a uniformly accelerated body, the force of inertia is directed opposite to the acceleration. From the total force of inertia, for convenience, the centrifugal force directed from the axis of rotation of the body, and the Coriolis force, which arises when the body moves relative to the rotating frame of reference, can be distinguished for convenience.
There are other forces as well.

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It is necessary to know the point of application and the direction of each force. It is important to be able to determine exactly what forces act on the body and in what direction. Force is denoted as , measured in Newtons. In order to distinguish between forces, they are designated as follows

Below are the main forces acting in nature. It is impossible to invent non-existent forces when solving problems!

There are many forces in nature. Here are considered the forces that are considered in school course physics in the study of dynamics. Other forces are also mentioned, which will be discussed in other sections.

Gravity

Every body on the planet is affected by the Earth's gravity. The force with which the Earth attracts each body is determined by the formula

The point of application is at the center of gravity of the body. Gravity always pointing vertically down.

Friction force

Let's get acquainted with the force of friction. This force arises when bodies move and two surfaces come into contact. The force arises as a result of the fact that the surfaces, when viewed under a microscope, are not smooth as they seem. The friction force is determined by the formula:

A force is applied at the point of contact between two surfaces. Directed in the direction opposite to the movement.

Support reaction force

Imagine a very heavy object lying on a table. The table bends under the weight of the object. But according to Newton's third law, the table acts on the object with exactly the same force as the object on the table. The force is directed opposite to the force with which the object presses on the table. That is up. This force is called the support reaction. The name of the force "speaks" react support. This force arises whenever there is an impact on the support. The nature of its occurrence molecular level. The object, as it were, deformed the usual position and connections of the molecules (inside the table), they, in turn, tend to return to their original state, "resist".

Absolutely any body, even a very light one (for example, a pencil lying on a table), deforms the support at the micro level. Therefore, a support reaction occurs.

There is no special formula for finding this force. They designate it with the letter, but this force is just a separate type of elastic force, so it can also be denoted as

The force is applied at the point of contact of the object with the support. Directed perpendicular to the support.

Since the body is represented as a material point, the force can be depicted from the center

Elastic force

This force arises as a result of deformation (changes in the initial state of matter). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress the spring, we decrease it. When we twist or shift. In all these examples, a force arises that prevents deformation - the elastic force.

Hooke's Law

The elastic force is directed opposite to the deformation.

Since the body is represented as a material point, the force can be depicted from the center

When connected in series, for example, springs, the stiffness is calculated by the formula

When connected in parallel, the stiffness

Sample stiffness. Young's modulus.

Young's modulus characterizes the elastic properties of a substance. This is constant, depending only on the material, its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.

More about properties solids.

Body weight

Body weight is the force with which an object acts on a support. You say it's gravity! The confusion occurs in the following: indeed often body weight equal to strength gravity, but these are completely different forces. Gravity is the force that results from interaction with the Earth. Weight is the result of interaction with the support. The force of gravity is applied at the center of gravity of the object, while the weight is the force that is applied to the support (not to the object)!

There is no formula for determining weight. This force is denoted by the letter .

The support reaction force or elastic force arises in response to the impact of an object on a suspension or support, therefore the body weight is always numerically the same as the elastic force, but has the opposite direction.

The reaction force of the support and the weight are forces of the same nature, according to Newton's 3rd law they are equal and oppositely directed. Weight is a force that acts on a support, not on a body. The force of gravity acts on the body.

Body weight may not be equal to gravity. It can be either more or less, or it can be such that the weight is zero. This state is called weightlessness. Weightlessness is a state when an object does not interact with a support, for example, a state of flight: there is gravity, but the weight is zero!

It is possible to determine the direction of acceleration if you determine where the resultant force is directed

Note that weight is a force, measured in Newtons. How to correctly answer the question: "How much do you weigh"? We answer 50 kg, naming not weight, but our mass! In this example, our weight is equal to gravity, which is approximately 500N!

Overload- the ratio of weight to gravity

Strength of Archimedes

Force arises as a result of the interaction of a body with a liquid (gas), when it is immersed in a liquid (or gas). This force pushes the body out of the water (gas). Therefore, it is directed vertically upwards (pushes). Determined by the formula:

In the air, we neglect the force of Archimedes.

If the Archimedes force is equal to the force of gravity, the body floats. If the Archimedes force is greater, then it rises to the surface of the liquid, if it is less, it sinks.

electrical forces

There are forces of electrical origin. Occur in the presence of an electric charge. These forces, such as the Coulomb force, Ampère force, Lorentz force, are discussed in detail in the Electricity section.

Schematic designation of the forces acting on the body

Often the body is modeled by a material point. Therefore, in the diagrams, various points of application are transferred to one point - to the center, and the body is schematically depicted as a circle or rectangle.

In order to correctly designate the forces, it is necessary to list all the bodies with which the body under study interacts. Determine what happens as a result of interaction with each: friction, deformation, attraction, or maybe repulsion. Determine the type of force, correctly indicate the direction. Attention! The number of forces will coincide with the number of bodies with which the interaction takes place.

The main thing to remember

Friction forces

Distinguish between external (dry) and internal (viscous) friction. External friction occurs between solid surfaces in contact, internal friction occurs between layers of liquid or gas during their relative motion. There are three types of external friction: static friction, sliding friction and rolling friction.

Rolling friction is determined by the formula

The resistance force arises when a body moves in a liquid or gas. The magnitude of the resistance force depends on the size and shape of the body, the speed of its movement and the properties of the liquid or gas. At low speeds, the resistance force is proportional to the speed of the body

At high speeds it is proportional to the square of the speed

The relationship between gravity, the law of gravity and the acceleration of free fall

Consider the mutual attraction of an object and the Earth. Between them, according to the law of gravity, a force arises Now let's compare the law of gravity and the force of gravity

The value of free fall acceleration depends on the mass of the Earth and its radius! Thus, it is possible to calculate with what acceleration objects on the Moon or on any other planet will fall, using the mass and radius of that planet.

The distance from the center of the Earth to the poles is less than to the equator. Therefore, the acceleration of free fall at the equator is slightly less than at the poles. At the same time, it should be noted that the main reason for the dependence of the acceleration of free fall on the latitude of the area is the fact that the Earth rotates around its axis.

When moving away from the surface of the Earth, the force of gravity and the acceleration of free fall change inversely with the square of the distance to the center of the Earth.

>>Physics: Forces in nature. Gravitational forces

Let us first find out whether there are many kinds of forces in nature.
At first glance, it seems that we have taken on an overwhelming and insoluble task: bodies on Earth and outside it. infinite set. They interact differently. So, for example, a stone falls to the Earth; an electric locomotive pulls a train; the football player's foot hits the ball; an ebonite stick worn on fur attracts light pieces of paper, a magnet attracts iron filings; a conductor with current turns the compass needle; the Moon and the Earth interact, and together they interact with the Sun; stars and star systems interact, etc. Similar examples there is no end. It seems that in nature there are an infinite number of interactions (forces)? It turns out not!
Four types of forces. In the boundless expanses of the Universe, on our planet, in any substance, in living organisms, in atoms, in atomic nuclei and in the world of elementary particles, we meet with the manifestation of only four types of forces: gravitational, electromagnetic, strong (nuclear) and weak.
Gravitational forces, or the forces of universal gravitation, act between all bodies - all bodies are attracted to each other. But this attraction is usually essential only when at least one of the interacting bodies is as large as the Earth or the Moon. Otherwise, these forces are so small that they can be neglected.
Electromagnetic forces act between particles that have electric charges. The scope of their activities is especially extensive and varied. In atoms, molecules, solid, liquid and gaseous bodies, living organisms, electromagnetic forces are the main ones. Their role in atoms is great.
Scope nuclear forces very limited. They are only visible inside. atomic nuclei(i.e., at distances of the order of 10 -13 cm). Already at distances between particles of the order of 10 -11 cm (a thousand times smaller than the size of an atom - 10 -8 cm), they do not appear at all.
Weak interactions manifest themselves at even shorter distances, on the order of 10 -15 cm. They cause mutual transformations of elementary particles, determine the radioactive decay of nuclei, and thermonuclear fusion reactions.
Nuclear forces are the most powerful in nature. If the intensity of nuclear forces is taken as unity, then the intensity of electromagnetic forces will be 10 -2 , gravitational - 10 -40 , weak interactions - 10 -16 .
Strong (nuclear) and weak interactions manifest themselves at such small distances when the laws of Newtonian mechanics, and together with them the concept mechanical force lose their meaning.
In mechanics, we will consider only gravitational and electromagnetic interactions.
Forces in mechanics. In mechanics, they usually deal with three types of forces - gravitational forces, elastic forces and friction forces.
The forces of elasticity and friction are of an electromagnetic nature. We will not explain here the origin of these forces, with the help of experiments it will be possible to find out the conditions under which these forces arise, and to express them quantitatively.
There are four types of interaction in nature. In mechanics, gravitational forces and two types of electromagnetic forces are studied - elastic forces and friction forces.

G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics Grade 10

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There are four types of forces in nature: gravitational, electromagnetic, nuclear and weak.

gravitational forces, or gravitational force, operate between all bodies. But these forces are noticeable if at least one of the bodies has dimensions commensurate with the dimensions of the planets. The forces of attraction between ordinary bodies are so small that they can be neglected. Therefore, gravitational forces can be considered the forces of interaction between the planets, as well as between the planets and the Sun or other bodies that have a very large mass. These can be stars, satellites of planets, etc.

Electromagnetic forces act between bodies that have an electric charge.

nuclear forces(strong) are the most powerful in nature. They act inside the nuclei of atoms at distances of 10 -13 cm.

Weak Forces, like nuclear ones, act at small distances of the order of 10 -15 cm. As a result of their action, processes occur inside the nucleus.

Mechanics considers gravitational forces, elastic forces and frictional forces.

Gravitational forces

Gravity is described the law of universal gravitation. This law was outlined by Newton in the middle XVII in. in Mathematical Principles of Natural Philosophy.

Gravitycalled the gravitational force with which any material particles are attracted to each other.

The force with which material particles are attracted to each other is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. .

G - gravitational constant, numerically equal to the modulus of the gravitational force, with which a body having a unit mass acts on a body having the same unit mass and located on unit distance From him.

G \u003d 6.67384 (80) 10 −11 m 3 s −2 kg −1, or N m² kg −2.

On the surface of the Earth, the gravitational force (gravitational force) manifests itself in the form gravity.

We see that any object thrown in a horizontal direction still falls down. Any object thrown up also falls down. This is due to the force of gravity acting on any material body located near the surface of the Earth. Gravity acts on bodies and on the surfaces of other astronomical bodies. This force is always directed vertically downwards.

Under the influence of gravity, the body moves to the surface of the planet with an acceleration called free fall acceleration.

The free fall acceleration on the Earth's surface is denoted by the letter g .

F t = mg ,

hence,

g = F t / m

g \u003d 9.81 m / s 2 at the poles of the Earth, and at the equator g \u003d 9.78 m / s 2.

When solving simple physical problems, the quantity g it is considered to be equal to 9.8 m / s 2.

The classical theory of gravitation is applicable only for bodies with a speed much lower than the speed of light.

elastic forces

Forces of elasticity called the forces that arise in the body as a result of deformation, causing change its shape or volume. These forces always strive to return the body to its original position.

During deformation, the particles of the body are displaced. The elastic force is directed in the direction opposite to the direction of particle displacement. If the deformation stops, the elastic force disappears.

The English physicist Robert Hooke, a contemporary of Newton, discovered a law establishing a relationship between the force of elasticity and the deformation of a body.

When the body is deformed, an elastic force arises, which is directly proportional to the elongation of the body, and has a direction opposite to the movement of particles during deformation.

F = k ∆ l ,

where to is the rigidity of the body, or coefficient of elasticity;

∆ l - the amount of deformation, showing the amount of elongation of the body under the influence of elastic forces.

Hooke's law is valid for elastic deformations when the elongation of the body is small, and the body restores its original dimensions after the forces that caused this deformation disappear.

If the deformation is large and the body does not return to its original shape, Hooke's law does not apply. At very large deformations, the destruction of the body occurs.

Friction forces

Friction occurs when one body moves over the surface of another. It has an electromagnetic nature. This is a consequence of the interaction between atoms and molecules of adjoining bodies. The direction of the friction force is opposite to the direction of motion.

Distinguish dry and liquid friction. Friction is called dry if there is no liquid or gaseous layer between the bodies.

A distinctive feature of dry friction is static friction, which occurs when bodies are at relative rest.

Value static friction forces always equal to the magnitude of the external force and directed in the opposite direction. The static friction force prevents the body from moving.

In turn, dry friction is divided into friction slip and friction rolling.

If the magnitude of the external force exceeds the magnitude of the friction force, then in this case slippage will appear, and one of the contacting bodies will begin to move forward relative to the other body. And the force of friction will be called sliding friction force. Its direction will be opposite to the direction of sliding.

The sliding friction force depends on the force with which the bodies press on each other, on the state of the rubbing surfaces, on the speed of movement, but does not depend on the contact area.

The sliding friction force of one body on the surface of another is calculated by the formula:

F tr. = k N ,

where k- coefficient of sliding friction;

N - force normal reaction acting on the body from the side of the surface.

Rolling friction force occurs between a body that rolls over a surface and the surface itself. Such forces appear, for example, when the tires of a car come into contact with the road surface.

The value of the rolling friction force is calculated by the formula

where F t – rolling friction force;

f is the coefficient of rolling friction;

R is the radius of the rolling body;

N - pressing force.