General characteristics of the concept "power". Physics - remember everything
1. Newton's laws of dynamics
laws or axioms of motion (as formulated by Newton himself in the book “Mathematical Principles of Natural Philosophy” of 1687): “I. Every body continues to be maintained in its state of rest or uniform and rectilinear motion until and unless it is forced by applied forces to change this state. II. The change in momentum is proportional to the applied driving force and occurs in the direction of the straight line along which this force acts. III. An action always has an equal and opposite reaction, otherwise the interactions of two bodies on each other are equal and directed in opposite directions.”
2. What is force?
Force is characterized by magnitude and direction. Force characterizes the action of other bodies on a given body. The result of a force acting on a body depends not only on its magnitude and direction, but also on the point of application of the force. Resultant is one force, the result of which will be the same as the result of the action of all real forces. If the forces are co-directed, the resultant is equal to their sum and directed in the same direction. If the forces are directed in opposite directions, then the resultant is equal to their difference and is directed towards the greater force.
Gravity and body weight
Gravity is the force with which a body is attracted to the Earth due to universal gravitation. All bodies in the Universe are attracted to each other, and the greater their mass and the closer they are located, the stronger the attraction.
To calculate the force of gravity, the body mass should be multiplied by a coefficient denoted by the letter g, approximately equal to 9.8 N/kg. Thus, the force of gravity is calculated by the formula
Body weight is the force with which the body presses on a support or stretches a suspension due to attraction to the Earth. If a body has neither support nor suspension, then the body has no weight - it is in a state of weightlessness.
Elastic force
Elastic force is a force that arises inside a body as a result of deformation and prevents a change in shape. Depending on how the shape of the body changes, several types of deformation are distinguished, in particular, tension and compression, bending, shear and shear, and torsion.
The more the shape of a body is changed, the greater the elastic force generated in it.
A dynamometer is a device for measuring force: the measured force is compared with the elastic force arising in the spring of the dynamometer.
Friction force
The force of static friction is the force that prevents a body from moving from its place.
The reason friction occurs is that any surface has irregularities that engage each other. If the surfaces are polished, then the cause of friction is the forces of molecular interaction. When a body moves on a horizontal surface, the friction force is directed against the movement and is directly proportional to the force of gravity:
The sliding friction force is the resistance force when one body slides over the surface of another. The rolling friction force is the resistance force when one body rolls over the surface of another; it is significantly less than the sliding friction force.
If friction is useful, it is increased; if it is harmful, reduce it.
3. CONSERVATION LAWS
CONSERVATION LAWS, physical laws according to which some property of a closed system remains unchanged despite any changes in the system. The most important are laws of conservation of matter and energy. The law of conservation of matter states that matter is neither created nor destroyed; During chemical transformations, the total mass remains unchanged. The total amount of energy in the system also remains unchanged; energy is only converted from one form to another. Both of these laws are only approximately correct. Mass and energy can be converted into one another according to the equation E = ts 2. Only the total amount of mass and its equivalent energy remains unchanged. Another conservation law concerns electric charge: it also cannot be created and cannot be destroyed. When applied to nuclear processes, the conservation law is expressed in the fact that the total charge, spin and other QUANTUM NUMBERS of interacting particles must remain the same for the particles resulting from the interaction. In strong interactions, all quantum numbers are conserved. In weak interactions, some of the requirements of this law are violated, especially with regard to PARITY.
The law of conservation of energy can be explained using the example of a ball weighing 1 kg falling from a height of 100 m. The initial total energy of the ball is its potential energy. When it falls, the potential energy gradually decreases and the kinetic energy increases, but the total amount of energy remains unchanged. Thus, conservation of energy takes place. A - kinetic energy increases from 0 to maximum: B - potential energy decreases from maximum to zero; C is the total amount of energy, which is equal to the sum of kinetic and poten The law of conservation of matter states that during chemical reactions matter is neither created nor destroyed. This phenomenon can be demonstrated using a classical experiment in which a candle burning under a glass bell is weighed (A). At the end of the experiment, the weight of the cap and its contents remained the same as it was at the beginning, although the candle, the substance of which consists mainly of carbon and hydrogen, “disappeared”, since volatile reaction products (water and carbon dioxide) were released from it. Only after scientists recognized the principle of conservation of matter at the end of the 18th century did a quantitative approach to chemistry become possible.
Mechanical work occurs when a body moves under the influence of a force applied to it.
Mechanical work is directly proportional to the distance traveled and proportional to the force:
Power
The speed of performing work in technology is characterized by power.
Power is equal to the ratio of work to the time during which it was performed:
Energy This is a physical quantity that shows how much work a body can do. Energy is measured in joules.
When work is done, the energy of bodies is measured. Work done is equal to the change in energy.
Potential energy determined by the relative position of interacting bodies or parts of the same body.
E p = F h = gmh.
Where g = 9.8 N/kg, m is body weight (kg), h is height (m).
Kinetic energy possesses a body as a result of its movement. The greater the body's mass and speed, the greater its kinetic energy.
5. basic law of dynamics of rotational motion
Moment of power
1. Moment of force relative to the axis of rotation, (1.1) where is the projection of the force onto a plane perpendicular to the axis of rotation, is the arm of the force (the shortest distance from the axis of rotation to the line of action of the force).
2. Moment of force relative to a fixed point O (origin). (1.2) It is determined by the vector product of the radius vector drawn from point O to the point of application of the force by this force; - a pseudo-vector, its direction coincides with the direction of translational motion of the right screw when it rotates away (“gimlet rule”). Modulus of the moment of force, (1.3) where is the angle between the vectors and is the arm of the force, the shortest distance between the line of action of the force and the point of application of the force.
Momentum
1. Momentum of momentum of a body rotating about the axis, (1.4) where is the moment of inertia of the body, is the angular velocity. The angular momentum of a system is the vector sum of the angular momentum of all bodies in the system: 
.
(1.5)
2. Momentum of a material point with momentum relative to a fixed point O (origin). (1.6) It is determined by the vector product of the radius vector drawn from point O to the material point by the momentum vector; - pseudo-vector, its direction coincides with the direction of translational motion of the right propeller when it rotates away (“gimlet rule”). Modulus of the angular momentum vector, (1.7) where is the angle between the vectors and is the arm of the vector relative to point O.
Moment of inertia about the axis of rotation
1. Moment of inertia of a material point, (1.8) where is the mass of the point, is its distance from the axis of rotation.
2. Moment of inertia of a discrete rigid body, (1.9) where is the element of mass of the rigid body; is the distance of this element from the axis of rotation; is the number of elements of the body.
3. Moment of inertia in the case of continuous mass distribution (solid solid body). (1.10) If the body is homogeneous, i.e. its density is the same throughout the entire volume, then the expression (1.11) is used, where and is the volume of the body.
It is necessary to know the point of application and direction of each force. It is important to be able to determine which 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 operating in nature. It is impossible to invent forces that do not exist when solving problems!
There are many forces in nature. Here we consider the forces that are considered in the school physics course when studying dynamics. Other forces are also mentioned, which will be discussed in other sections.
Gravity
Every body on the planet is affected by 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 directed vertically downwards.
Friction force
Let's get acquainted with the force of friction. This force occurs when bodies move and two surfaces come into contact. The force occurs because surfaces, when viewed under a microscope, are not as smooth as they appear. The friction force is determined by the formula:
The force is applied at the point of contact of two surfaces. Directed in the direction opposite to movement.
Ground reaction force
Let's 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 ground reaction. The name of the force "speaks" support reacts. This force occurs whenever there is an impact on the support. The nature of its occurrence at the molecular level. The object seemed to deform the usual position and connections of the molecules (inside the table), they, in turn, strive 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 ground reaction occurs.
There is no special formula for finding this force. It is denoted by the letter , but this force is simply a separate type of elasticity 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, force can be represented from the center
Elastic force
This force arises as a result of deformation (change in the initial state of the substance). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress a 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, force can be represented from the center
When connecting springs in series, for example, the stiffness is calculated using 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 a constant value that depends only on the material and its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.
Read more about properties of solids.
Body weight
Body weight is the force with which an object acts on a support. You say, this is the force of gravity! The confusion occurs in the following: indeed, often the weight of a body is equal to the force of gravity, but these forces are completely different. Gravity is a force that arises as a result of interaction with the Earth. Weight is the result of interaction with support. The force of gravity is applied at the center of gravity of the object, while weight is the force that is applied to the support (not to the object)!
There is no formula for determining weight. This force is designated by the letter.
The support reaction force or elastic force arises in response to the impact of an object on the suspension or support, therefore the weight of the body is always numerically the same as the elastic force, but has the opposite direction.
The support reaction force and 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 the support, not on the body. The force of gravity acts on the body.
Body weight may not be equal to gravity. It may be more or less, or it may be that the weight is zero. This condition is called weightlessness. Weightlessness is a state when an object does not interact with a support, for example, the 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
Please note that weight is force, measured in Newtons. How to correctly answer the question: “How much do you weigh”? We answer 50 kg, not naming our weight, but our mass! In this example, our weight is equal to gravity, that is, approximately 500N!
Overload- ratio of weight to gravity
Archimedes' force
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 upward (pushes). Determined by the formula:
In the air we neglect the power 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 less, it sinks.
Electrical forces
There are forces of electrical origin. Occurs in the presence of an electrical charge. These forces, such as the Coulomb force, Ampere force, Lorentz force, are discussed in detail in the section Electricity.
Schematic designation of forces acting on a body
Often a body is modeled as a material point. Therefore, in diagrams, various points of application are transferred to one point - to the center, and the body is depicted schematically as a circle or rectangle.
In order to correctly designate 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 and correctly indicate the direction. Attention! The amount of forces will coincide with the number of bodies with which the interaction occurs.
The main thing to remember
1) Forces and their nature;
2) Direction of forces;
3) Be able to identify the acting forces
There are external (dry) and internal (viscous) friction. External friction occurs between contacting solid surfaces, 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 occurs 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 of movement, the drag force is proportional to the speed of the body
At high speeds it is proportional to the square of the speed
Let's 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 magnitude of the acceleration due to gravity 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 gravity 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 gravity on the latitude of the area is the fact of the Earth’s rotation around its axis.
As we move away from the Earth's surface, the force of gravity and the acceleration of gravity change in inverse proportion to the square of the distance to the center of the Earth.
Force is a physical quantity that is a measure of the interaction between bodies. That is, force is a measure of the influence of one body on another and vice versa. In physics, there are a huge number of different types of forces, for example: friction force, elastic force, gravity force and so on. However, all forces are united by the fact that they are characterized by certain components.
What is strength characterized by?
In physics, any force is described by three components:
- Direction. Since force is a vector physical quantity, it has a direction that shows where the force acts.
- Absolute value (modulus) of force. Any vector is characterized by a magnitude. The force modulus is the length of the force vector.
- Point of application of force. Since force is a vector, it can only be plotted from a certain point in the plane (space). This point is called the point of application of force.
Thus, to describe any force acting on a body, it is necessary to specify only these three components: direction, modulus, point of application.
The action of a force on a body leads to a change in its speed or deformation. The greater the force, the more the speed of the body changes or the greater its deformation.
Force is a vector physical quantity that shows how one body interacts with another body or field. It shows the direction and intensity of this interaction. Force is a measure of the interaction of bodies or fields.
Force is measured in Newtons.
A force of 1 N is the force that changes the speed of a body weighing 1 kg in 1 s by 1 m/s.
1.Strength- vector physical quantity, which is a measure of the intensity of impact on a given body other bodies, as well as fields Attached to massive force in the body is the reason for its change speed or occurrence in it deformations and stresses.
Force as a vector quantity is characterized module, direction And "point" of the application strength. By the last parameter, the concept of force as a vector in physics differs from the concept of a vector in vector algebra, where vectors equal in magnitude and direction, regardless of the point of their application, are considered the same vector. In physics, these vectors are called free vectors. In mechanics, the idea of coupled vectors is extremely common, the beginning of which is fixed at a certain point in space or can be located on a line that continues the direction of the vector (sliding vectors).
The concept is also used line of force, denoting the straight line passing through the point of application of the force along which the force is directed.
Newton's second law states that in inertial reference systems, the acceleration of a material point in direction coincides with the resultant of all forces applied to the body, and in magnitude is directly proportional to the magnitude of the force and inversely proportional to the mass of the material point. Or, equivalently, the rate of change of momentum of a material point is equal to the applied force.
When a force is applied to a body of finite dimensions, mechanical stresses arise in it, accompanied by deformations.
From the point of view of the Standard Model of particle physics, fundamental interactions (gravitational, weak, electromagnetic, strong) are carried out through the exchange of so-called gauge bosons. Experiments in high energy physics conducted in the 70−80s. XX century confirmed the assumption that the weak and electromagnetic interactions are manifestations of the more fundamental electroweak interaction.
The dimension of force is LMT −2, the unit of measurement in the International System of Units (SI) is newton (N, N), in the GHS system it is dyne.
2.Newton's first law.
Newton's first law states that there are frames of reference in which bodies maintain a state of rest or uniform rectilinear motion in the absence of actions on them from other bodies or in the case of mutual compensation of these influences. Such reference systems are called inertial. Newton proposed that every massive object has a certain reserve of inertia, which characterizes the “natural state” of motion of that object. This idea rejects the view of Aristotle, who considered rest to be the “natural state” of an object. Newton's first law contradicts Aristotelian physics, one of the provisions of which is the statement that a body can move at a constant speed only under the influence of force. The fact that in Newtonian mechanics in inertial frames of reference rest is physically indistinguishable from uniform rectilinear motion is the rationale for Galileo's principle of relativity. Among a set of bodies, it is fundamentally impossible to determine which of them are “in motion” and which are “at rest.” We can talk about motion only relative to some reference system. The laws of mechanics are satisfied equally in all inertial frames of reference, in other words, they are all mechanically equivalent. The latter follows from the so-called Galilean transformations.
3.Newton's second law.
Newton's second law in its modern formulation sounds like this: in an inertial frame of reference, the rate of change of momentum of a material point is equal to the vector sum of all forces acting on this point.
where is the momentum of the material point, is the total force acting on the material point. Newton's second law states that the action of unbalanced forces leads to a change in the momentum of a material point.
By definition of momentum:
where is mass, is speed.
In classical mechanics, at speeds much lower than the speed of light, the mass of a material point is considered unchanged, which allows it to be taken out of the differential sign under these conditions:
Given the definition of the acceleration of a point, Newton's second law takes the form:
It is considered to be "the second most famous formula in physics", although Newton himself never explicitly wrote his second law in this form. For the first time this form of the law can be found in the works of K. Maclaurin and L. Euler.
Since in any inertial reference frame the acceleration of the body is the same and does not change when transitioning from one frame to another, then the force is invariant with respect to such a transition.
In all natural phenomena force, regardless of your origin, appears only in a mechanical sense, that is, as the reason for the violation of the uniform and rectilinear motion of the body in the inertial coordinate system. The opposite statement, i.e. establishing the fact of such movement, does not indicate the absence of forces acting on the body, but only that the actions of these forces are mutually balanced. Otherwise: their vector sum is a vector with modulus equal to zero. This is the basis for measuring the magnitude of a force when it is compensated by a force whose magnitude is known.
Newton's second law allows us to measure the magnitude of a force. For example, knowledge of the mass of a planet and its centripetal acceleration when moving in orbit allows us to calculate the magnitude of the gravitational attraction force acting on this planet from the Sun.
4.Newton's third law.
For any two bodies (let's call them body 1 and body 2), Newton's third law states that the force of action of body 1 on body 2 is accompanied by the appearance of a force equal in magnitude, but opposite in direction, acting on body 1 from body 2. Mathematically, the law is written So:
This law means that forces always occur in action-reaction pairs. If body 1 and body 2 are in the same system, then the total force in the system due to the interaction of these bodies is zero:
This means that there are no unbalanced internal forces in a closed system. This leads to the fact that the center of mass of a closed system (that is, one that is not acted upon by external forces) cannot move with acceleration. Individual parts of the system can accelerate, but only in such a way that the system as a whole remains in a state of rest or uniform linear motion. However, if external forces act on the system, its center of mass will begin to move with acceleration proportional to the external resultant force and inversely proportional to the mass of the system.
5.Gravity.
Gravity ( gravity) - universal interaction between any types of matter. Within the framework of classical mechanics, it is described by the law of universal gravitation, formulated by Isaac Newton in his work “Mathematical Principles of Natural Philosophy”. Newton obtained the magnitude of the acceleration with which the Moon moves around the Earth, assuming in his calculation that the force of gravity decreases in inverse proportion to the square of the distance from the gravitating body. In addition, he also established that the acceleration caused by the attraction of one body by another is proportional to the product of the masses of these bodies. Based on these two conclusions, the law of gravitation was formulated: any material particles are attracted towards each other with a force directly proportional to the product of masses ( and ) and inversely proportional to the square of the distance between them:
Here is the gravitational constant, the value of which was first obtained by Henry Cavendish in his experiments. Using this law, you can obtain formulas for calculating the gravitational force of bodies of arbitrary shape. Newton's theory of gravity well describes the motion of the planets of the solar system and many other celestial bodies. However, it is based on the concept of long-range action, which contradicts the theory of relativity. Therefore, the classical theory of gravity is not applicable to describe the motion of bodies moving at speeds close to the speed of light, the gravitational fields of extremely massive objects (for example, black holes), as well as the variable gravitational fields created by moving bodies at large distances from them.
A more general theory of gravity is Albert Einstein's general theory of relativity. In it, gravity is not characterized by an invariant force independent of the reference frame. Instead, the free movement of bodies in a gravitational field, perceived by the observer as movement along curved trajectories in three-dimensional space-time with variable speed, is considered as inertial movement along a geodesic line in a curved four-dimensional space-time, in which time flows differently at different points . Moreover, this line is in a sense “the most direct” - it is such that the space-time interval (proper time) between two space-time positions of a given body is maximum. The curvature of space depends on the mass of bodies, as well as on all types of energy present in the system.
6.Electrostatic field (field of stationary charges).
The development of physics after Newton added to the three main quantities (length, mass, time) an electric charge with dimension C. However, based on the requirements of practice, they began to use not a unit of charge, but a unit of electric current as the main unit of measurement. Thus, in the SI system, the basic unit is the ampere, and the unit of charge, the coulomb, is a derivative of it.
Since the charge, as such, does not exist independently of the body carrying it, the electrical interaction of bodies manifests itself in the form of the same force considered in mechanics, which serves as the cause of acceleration. In relation to the electrostatic interaction of two point charges of magnitude and located in a vacuum, Coulomb's law is used. In the form corresponding to the SI system, it looks like:
where is the force with which charge 1 acts on charge 2, is the vector directed from charge 1 to charge 2 and is equal in magnitude to the distance between the charges, and is the electrical constant equal to ≈ 8.854187817 10 −12 F/m. When charges are placed in a homogeneous and isotropic medium, the interaction force decreases by a factor of ε, where ε is the dielectric constant of the medium.
The force is directed along the line connecting the point charges. Graphically, the electrostatic field is usually depicted as a picture of lines of force, which are imaginary trajectories along which a charged particle without mass would move. These lines start on one charge and end on another.
7.Electromagnetic field (direct current field).
The existence of a magnetic field was recognized back in the Middle Ages by the Chinese, who used the “loving stone” - a magnet, as a prototype of a magnetic compass. Graphically, a magnetic field is usually depicted in the form of closed lines of force, the density of which (as in the case of an electrostatic field) determines its intensity. Historically, a visual way to visualize a magnetic field was with iron filings sprinkled, for example, on a piece of paper placed on a magnet.
Oersted established that the current flowing through a conductor causes a deflection of the magnetic needle.
Faraday came to the conclusion that a magnetic field is created around a current-carrying conductor.
Ampere put forward a hypothesis, recognized in physics, as a model of the process of the emergence of a magnetic field, which consists in the existence in materials of microscopic closed currents, which together provide the effect of natural or induced magnetism.
Ampere established that in a reference frame located in a vacuum, in relation to which the charge is in motion, that is, it behaves like an electric current, a magnetic field arises, the intensity of which is determined by the magnetic induction vector lying in a plane located perpendicular to the direction charge movement.
The unit of measurement of magnetic induction is tesla: 1 T = 1 T kg s −2 A −2
The problem was solved quantitatively by Ampere, who measured the force of interaction of two parallel conductors with currents flowing through them. One of the conductors created a magnetic field around itself, the second reacted to this field by approaching or moving away with a measurable force, knowing which and the magnitude of the current it was possible to determine the module of the magnetic induction vector.
The force interaction between electric charges that are not in motion relative to each other is described by Coulomb's law. However, charges in motion relative to each other create magnetic fields, through which currents created by the movement of charges generally come into a state of force interaction.
The fundamental difference between the force that arises during the relative motion of charges and the case of their stationary placement is the difference in the geometry of these forces. For the case of electrostatics, the forces of interaction between two charges are directed along the line connecting them. Therefore, the geometry of the problem is two-dimensional and consideration is carried out in a plane passing through this line.
In the case of currents, the force characterizing the magnetic field created by the current is located in a plane perpendicular to the current. Therefore, the picture of the phenomenon becomes three-dimensional. The magnetic field created by an infinitely small element of the first current, interacting with the same element of the second current, generally creates a force acting on it. Moreover, for both currents this picture is completely symmetrical in the sense that the numbering of currents is arbitrary.
The law of interaction of currents is used to standardize direct electric current.
8.Strong interaction.
The strong force is the fundamental short-range interaction between hadrons and quarks. In the atomic nucleus, the strong force holds together positively charged (experiencing electrostatic repulsion) protons through the exchange of pi mesons between nucleons (protons and neutrons). Pi mesons have a very short lifespan; their lifetime is only enough to provide nuclear forces within the radius of the nucleus, which is why nuclear forces are called short-range. An increase in the number of neutrons “dilutes” the nucleus, reducing electrostatic forces and increasing nuclear ones, but with a large number of neutrons, they themselves, being fermions, begin to experience repulsion due to the Pauli principle. Also, when nucleons come too close, an exchange of W bosons begins, causing repulsion, thanks to which atomic nuclei do not “collapse.”
Within the hadrons themselves, the strong interaction holds together the quarks - the constituent parts of hadrons. Strong field quanta are gluons. Each quark has one of three “color” charges, each gluon consists of a “color”-“anticolor” pair. Gluons bind quarks in the so-called. “confinement”, due to which free quarks have not been observed in the experiment at the moment. As quarks move away from each other, the energy of gluon bonds increases, and does not decrease as in nuclear interaction. By spending a lot of energy (by colliding hadrons in an accelerator), you can break the quark-gluon bond, but at the same time a jet of new hadrons is released. However, free quarks can exist in space: if some quark managed to avoid confinement during the Big Bang, then the probability of annihilation with the corresponding antiquark or turning into a colorless hadron for such a quark is vanishingly small.
9.Weak interaction.
The weak interaction is a fundamental short-range interaction. Range 10 −18 m. Symmetrical with respect to the combination of spatial inversion and charge conjugation. All fundamental elements are involved in weak interaction.fermions (leptons And quarks). This is the only interaction that involvesneutrino(not to mention gravity, negligible in laboratory conditions), which explains the colossal penetrating ability of these particles. The weak interaction allows leptons, quarks and theirantiparticles exchange energy, mass, electric charge And quantum numbers- that is, turn into each other. One of the manifestations isbeta decay.
Mechanical interaction is one of the types of interaction of matter that can cause a change in the mechanical movement of material bodies.
Force characterizes the quantitative side of mechanical interaction. Thus, when they say that forces act on a body, this means that other bodies (or physical fields) act on it. Not always, however, force actually leads to a change in the movement of the body; such a change can be blocked by the action of other forces. With this in mind, let's write:
Force (Newtonian) – a measure of mechanical influence on a certain material body from another material body (or physical field); it characterizes the intensity and direction of this impact. This, of course, is not a definition, but only an explanation of the concept of force. Since the concept of force is fundamental, its exact meaning is revealed in the axioms of mechanics.
For now, we will note this. The “Newtonian” clause was made because in dynamics we will encounter other quantities, also called forces, which, however, are not measures of mechanical interaction. In this same semester we will talk specifically about Newtonian forces, and for brevity we will simply call them forces.
Further, the word “measure” in mechanics and physics is understood as a physical quantity that serves to quantitatively describe a property or relationship. In this case, we are talking about describing precisely the mechanical interaction (and, as you know, there are also other interactions - thermal, chemical and others).
In particle physics, there are four fundamental interactions: strong, electromagnetic, weak and gravitational. These four interactions underlie all observable phenomena - both in mechanics and in other branches of natural science.
However, in the macrocosm, fundamental interactions manifest themselves, as a rule, indirectly, and we have to deal with a much wider list of interactions (no longer necessarily fundamental). If we talk about mechanical interactions, then we can talk about forces of various origins.
Examples of forces: gravity, elasticity, Archimedean forces, environmental resistance forces, etc. In most problems of mechanics, however, the physical nature of certain forces is usually not of interest.
While explaining the concept of force, we also talked about the intensity and direction of influence. This means that force is a vector quantity. Namely, this is a vector applied to a certain point of a material body. Therefore, we can talk about such characteristics of force.
Strength is characterized by:
1) size (modulus);
3) application point.
Unfortunately, during the exam you often encounter complete disregard for this rule. In the best case scenario, the examiner in this situation will do the following: he will sigh and ask the student to quickly put down vector designations in the text of the answer to the question posed. If a student fails to put down the notations correctly, this is the first step towards getting a “D”. Therefore, please do not ignore the line in your notes if it is written on the board.
Parentheses with a comma in the middle denote the scalar product of vectors (the comma separates the factors). Please note: in many books, the dot product is denoted differently - by a dot between the vectors, and the dot can usually be omitted.
But we will stick to just such notations (they are also quite common). Among other things, they avoid confusion (after all, the scalar product of vectors must be distinguished from the usual product of two scalars).
So far we have only talked about the force vector. But the concept of force is not reduced to the concept of its vector. The point of application of the force is also important: after all, if a force vector of the same magnitude and direction is applied at another point of the body, then its movement may change.
The following terminology is accepted in geometry. A free vector (or simply a vector) is a vector characterized only by its magnitude and direction. A connected vector is a vector characterized by its point of application. Sometimes such designations are used.
By u---.A we denote the associated vector obtained if the free vector u--- is applied at point A. Please note: here the point is not written in the middle of the line (as when multiplying numbers), but on its bottom line. Thus, we can draw the following conclusion. So force is a bound vector (full notation: F----.A).
Where we need to emphasize the presence of a force at a certain point of application, we will use this full designation. Where the point of application of the force is predetermined, we will use shorthand notation, denoting the force simply as F---- (i.e., the same as the force vector). The following must be said about the point of application of force: If a force acts on a material point, then this point itself serves as the point of application.
If a force acts on a material body, then the point of application is the point of the body (it can change over time). In the general case, the point of application of force cannot lie outside the body. If the body is absolutely solid, then this limitation can be removed; but we will talk about this later.
The question arises: how can one set the point of application of force in practice? Any point can be specified, for example, by its radius vector drawn from a certain pole. A pole is an arbitrarily selected point (the position of which is usually assumed to be known).
Since it says “usually”, you can completely ignore the text in brackets. It often happens like this: they took a certain point and declared it a pole (and from now on it will be considered as such). But to set the position of the point of application of the force, we just need to know the position of the pole. It is possible - but not necessary - to take the origin of the coordinate system as a pole.
Both designations are used, but the first is preferable: the vector is denoted by one letter, and the letter “r” reminds us that we are talking about a radius vector, or six scalars (Fx, Fy, Fz, xA, yA, zA). This is convenient, and this is done often. But you can also set the force in a different way, which we will consider in the next paragraph.
