Examples of the action of bodies on each other. Interaction of bodies: measure and types of interaction. Weak forces and radioactivity

Interaction of bodies

You can give any number of examples of body interaction. When you, while in a boat, begin to pull another rope, your boat will certainly move forward. By acting on the second boat, you force it to act on your boat.

If you kick a soccer ball, you will immediately feel the kick back on your foot. When two billiard balls collide, they change their speed, i.e. Both balls get acceleration. All this is a manifestation of the general law of interaction between bodies.

The actions of bodies on each other are in the nature of interaction not only during direct contact of bodies. Place, for example, two strong magnets with different poles facing each other on a smooth table, and you will immediately find that they will begin to move towards each other. The Earth attracts the Moon (universal gravity) and forces it to move along a curved path; in turn, the Moon also attracts the Earth (also the force of universal gravity). Although, naturally, in the frame of reference associated with the Earth, the acceleration of the earth caused by this force cannot be detected directly, it manifests itself in the form of tides.

Let us find out through experiment how the forces of interaction between two bodies are related. Rough measurements of forces can be made using the following experiments:

1 experience. Let's take two dynamometers, hook their hooks to each other, and holding the rings, we will stretch them, monitoring the readings of both dynamometers.

We will see that for any stretch, the readings of both dynamometers will be the same; This means that the force with which the first dynamometer acts on the second is equal to the force with which the second dynamometer acts on the first.

2 experience. Let's take a strong enough magnet and an iron bar and place them on the rollers to reduce friction on the table. We attach identical soft springs to the magnet and the bar, with their other ends hooked on the table. The magnet and the bar will attract each other and stretch the springs.

Experience shows that by the time the movement stops, the springs are stretched equally. This means that forces that are equal in magnitude and opposite in direction act on both bodies from the side of the springs.

Since the magnet is at rest, the force is equal in magnitude and opposite in direction to the force with which the block acts on it.

In the same way, the forces acting on the block from the magnet and the spring are equal in magnitude and opposite in direction.

Experience shows that the forces of interaction between two bodies are equal in magnitude and opposite in direction even in cases where the bodies are moving.

3 experience. Two people A and B stand on two carts that can roll on rails. They hold the ends of the rope in their hands. It is easy to find that no matter who pulls the rope, A or B, or both, the carts always begin to move at the same time and, moreover, in opposite directions. By measuring the accelerations of the carts, one can verify that the accelerations are inversely proportional to the masses of each of the carts (including the person). It follows that the forces acting on the carts are equal in magnitude.

Newton's first law. Inertial reference systems

As the first law of dynamics, Newton accepted the law established by Galileo: a material point maintains a state of rest or uniform linear motion until the influence of other bodies takes it out of this state.

Newton's first law shows that rest or uniform linear motion does not require any external influences to maintain it. This reveals a special dynamic property of bodies, called their inertia.

Accordingly, Newton's first law is called the law of inertia, and the movement of a body in the absence of influences from other bodies is called motion by inertia.

Mechanical motion is relative: its character for the same body can be different in different reference systems moving relative to each other. For example, an astronaut on board an artificial Earth satellite is motionless in the reference frame associated with the satellite. At the same time, in relation to the Earth, it moves together with the satellite in an elliptical orbit, i.e. not evenly or straight.

It is natural, therefore, that Newton’s first law should not be satisfied in every frame of reference. For example, a ball lying on the smooth floor of a ship's cabin, which moves in a straight line and uniformly, can begin to move along the floor without any influence on it from any bodies. To do this, it is enough that the speed of the ship begins to change.

The reference system in relation to which a material point, free from external influences, is at rest or moves uniformly and rectilinearly is called an inertial reference system. The content of the first law, Newton's first law, is essentially reduced to two statements: firstly, that all bodies have the property of inertia and, secondly, that there are inertial frames of reference.

Any two inertial reference systems can move relative to each other only translationally and, moreover, uniformly and rectilinearly. It has been experimentally established that the heliocentric reference system is practically inertial, the origin of which is located at the center of mass of the Solar system (approximately at the center of the Sun), and the axes are drawn in the direction of three distant stars, chosen, for example, so that the coordinate axes are mutually perpendicular.

The laboratory reference system, whose coordinate axes are rigidly connected to the Earth, is not inertial mainly due to the daily rotation of the Earth. However, the Earth rotates so slowly that the maximum normal acceleration of points on its surface during daily rotation does not exceed 0.034 m/. Therefore, in most practical problems, the laboratory frame of reference can be approximately considered inertial.

Inertial frames of reference play a special role not only in mechanics, but also in all other branches of physics. This is due to the fact that, according to Einstein's principle of relativity, the mathematical expression of any physical law must have the same form in all inertial frames of reference.

Force is a vector quantity that is a measure of the mechanical action on the body in question from other bodies. Mechanical interaction can occur both between directly contacting bodies (for example, during friction, when bodies press on each other), and between remote bodies. A special form of matter that connects particles of matter into unified systems and transmits the action of one particle to another at a finite speed is called a physical field, or simply a field.

The interaction between distant bodies is carried out through the gravitational and electromagnetic fields they create (for example, the attraction of planets to the Sun, the interaction of charged bodies, conductors with current, etc.). The mechanical action on a given body from other bodies manifests itself in two ways. It is capable of causing, firstly, a change in the state of mechanical motion of the body in question, and secondly, its deformation. Both of these manifestations of force can serve as a basis for measuring forces. For example, measuring forces using a spring dynamometer based on Hooke's law for longitudinal tension. Using the concept of force in mechanics, we usually talk about the movement and deformation of a body under the influence of forces applied to it.

In this case, of course, each force always corresponds to some body acting on the object under consideration with this force.

The force F is completely defined if its magnitude, direction in space and point of application are given. The straight line along which the force is directed is called the line of action of the force.

A field acting on a material point with a force F is called a stationary field if it does not change over time t, i.e. if at any point in the field the force F does not depend explicitly on time:

For the field to be stationary, it is necessary that the bodies creating it are at rest relative to the inertial frame of reference used when considering the field.

Simultaneous action of several forces on a material point M is equivalent to the action of one force, called the resultant, or resultant, force and equal to their geometric sum.

It represents the closing polygon of forces

Weight. Pulse

In classical mechanics, the mass of a material point is a positive scalar quantity, which is a measure of the inertia of this point. Under the influence of a force, a material point does not change its speed instantly, but gradually, i.e. acquires a finite acceleration, which is smaller, the greater the mass of the material point. To compare the masses of two material points, it is enough to measure the modules and accelerations acquired by these points under the action of the same force:

Typically, body weight is found by weighing on a lever scale.

In classical mechanics it is believed that:

a) The mass of a material point does not depend on the state of motion of the point, being its constant characteristic.

b) Mass is an additive quantity, i.e. the mass of a system (for example, a body) is equal to the sum of the masses of all material points that are part of this system.

c) The mass of a closed system remains unchanged during any processes occurring in this system (law of conservation of mass).

The density ρ of a body at a given point M is the ratio of the mass dm of a small element of the body, including point M, to the value dV of the volume of this element:

The dimensions of the element under consideration must be so small that by changing the density within its limits, intermolecular distances can be many times greater.

A body is called homogeneous if the density is the same at all its points. The mass of a homogeneous body is equal to the product of its density and volume:

Mass of a heterogeneous body:

where ρ is a function of coordinates, and integration is carried out over the entire volume of the body. The average density (ρ) of an inhomogeneous body is the ratio of its mass to volume: (ρ)=m/V.

The center of mass of a system of material points is called point C, the radius vector of which is equal to:

where and are the mass and radius vector of the i-th material point, n is the total number of material points in the system, and m= is the mass of the entire system.

Center of mass speed:

Vector quantity equal to the product of the mass of a material point and its speed is called momentum, or momentum, of this material point. The momentum of a system of material points is the vector p, equal to the geometric sum of the momenta of all material points of the system:

The momentum of the system is equal to the product of the mass of the entire system and the speed of its center of mass:

Newton's second law

The basic law of the dynamics of a material point is Newton’s second law, which talks about how the mechanical motion of a material point changes under the influence of forces applied to it. Newton's second law states: the rate of change of momentum ρ of a material point is equal to the force F acting on it, i.e.

where m and v are the mass and speed of the material point.

If several forces simultaneously act on a material point, then the force F in Newton’s second law must be understood as the geometric sum of all acting forces - both active and reaction forces, i.e. resultant force.

The vector quantity F dt is called the elementary impulse of force F for a short time dt of its action. The impulse of force F for a finite period of time from to is equal to a certain integral:

where F, in general, depends on time t.

According to Newton's second law, the change in the momentum of a material point is equal to the momentum of the force acting on it:

dp = F dt and ,

Where – the value of the momentum of the material point at the end () and at the beginning () of the time period under consideration.

Since in Newtonian mechanics the mass m of a material point does not depend on the state of motion of the point, then

Therefore, the mathematical expression of Newton's second law can also be represented in the form

where is the acceleration of a material point, r is its radius vector. Accordingly, the formulation of Newton's second law states: the acceleration of a material point coincides in direction with the force acting on it and is equal to the ratio of this force to the mass of the material point.

The tangential and normal acceleration of the material are determined by the corresponding components of the force F

where is the magnitude of the velocity vector of the material point, and R is the radius of curvature of its trajectory. The force imparting normal acceleration to a material point is directed towards the center of curvature of the point’s trajectory and is therefore called centripetal force.

If several forces simultaneously act on a material point , then its acceleration

Where . Consequently, each of the forces simultaneously acting on a material point imparts to it the same acceleration as if there were no other forces (the principle of independence of the action of forces).

The differential equation of motion of a material point is called the equation

In projections onto the axes of a rectangular Cartesian coordinate system, this equation has the form

where x, y and z are the coordinates of the moving point.

Newton's third law. Movement of the center of mass

The mechanical action of bodies on each other is manifested in the form of their interaction. This is evidenced by Newton's third law: two material points act on each other with forces that are numerically equal and directed in opposite directions along the straight line connecting these points.

If is the force acting on the i-th material point from the k-th side, and is the force acting on the k-th material point from the i-th side, then, according to Newton’s third law,

Forces are applied to different material points and can be mutually balanced only in those cases when these points belong to the same absolutely rigid body.

Newton's third law is an essential addition to the first and second laws. It allows you to move from the dynamics of a single material point to the dynamics of an arbitrary mechanical system (system of material points). From Newton's third law it follows that in any mechanical system the geometric sum of all internal forces is equal to zero:

where n is the number of material points included in the system, and .

Vector equal to the geometric sum of all external forces acting on the system is called the main vector of external forces:

where is the resultant of external forces applied to the i-th material point.

From Newton’s second and third laws it follows that the first derivative with respect to time t of the momentum p of a mechanical system is equal to the main vector of all external forces applied to the system,

.

This equation expresses the law of change in the momentum of the system.

Since , where m is the mass of the system, and is the speed of its center of mass, then the law of motion of the center of mass of a mechanical system has the form

, or ,

where is the acceleration of the center of mass. Thus, the center of mass of a mechanical system moves as a material point, the mass of which is equal to the mass of the entire system and which is acted upon by a force equal to the main vector of external forces applied to the system.

If the system under consideration is a rigid body that moves translationally, then the velocities of all points of the body and its center of mass are the same and equal to the velocity v of the body. Accordingly, the acceleration of the body and the basic equation for the dynamics of translational motion of a rigid body have the form

Argues that in inertial systems the acceleration of a body is proportional to the applied force, a physical quantity that is a quantitative measure of interaction. The magnitude of the force characterizing the interaction of bodies can be determined, for example, by the deformation of an elastic body additionally introduced into the system so that the interaction with it completely compensates for the original one. Proportionality factor...

The magnitude and direction of all forces acting in a mechanical system, and the mass of the material bodies of which it consists, and its behavior in time can be calculated with complete accuracy. It is Newton’s second law that gives all of classical mechanics its special charm - it begins to seem as if the entire physical world is structured like the most precise chronometer, and nothing in it escapes the eye...

Lesson objectives:

• Show experimentally how the velocities of bodies change when they interact. Introduce the concept of body mass as a physical quantity, a unit of measurement of mass in the SI system.
• Develop the ability to find the laws of physics in the world around us, explain phenomena and processes from everyday life from the point of view of physics. Develop attention and logic.
• Cultivate accuracy in notes, accuracy in the presentation of physical material, in the formulation of terms.

DURING THE CLASSES

I. Repetition of the theme “Inertia”(15 minutes)

• Give examples when the speed of a body changes under the influence of other bodies;
• How would a body move if no other bodies acted on it?
• What is called inertia?
• What kind of motion is called motion by inertia? Give examples.
• An excerpt from J. Hasek’s novel “The Adventures of the Good Soldier Švejk”: “When the gasoline ran out, the car was forced to stop... And after that they still talk about inertia, gentlemen!... Isn’t it funny?” Does the story told by Colonel Zillergut contradict the idea of ​​inertia? Why did the car stop? What body affected him?
• Where does a tripping person fall? Why? Which part of the human body maintains its speed and which part changes it?
• Where does a person slip fall? Why? Which part of the human body maintains its speed and which part changes it?
• Situational game: Students are bus passengers. Picture the situation:

The bus moved abruptly;
- the bus travels evenly and straightly;
- there is an unexpected obstacle ahead, the bus brakes sharply;
- turns right at high speed; left;
- drives evenly and straight;
- sudden stop.

Explain your behavior from a physics point of view.

• Work in pairs. Questions are asked to the children according to the options, they answer them to each other in pairs, then voice their answers in front of the class, correct mistakes, eliminate shortcomings, and complement the answers of their comrades:

Option I:
a) Explain shaking dust from a rug from the point of view of physics.
b) Why is there a speed limit sign before a sharp turn?
Option II:
a) Explain the method of attaching a hammer to the handle.
b) The hare, running away from the wolf, twists and turns. What physics phenomenon does the hare use to preserve its life? Explain.

• What is the braking distance of a car? Why is it dangerous to cross the road in front of nearby traffic in icy conditions?
• Physics in literature: The famous English writer Herbert Wells has a fantastic story about how a certain clerk worked miracles. As soon as he expressed any wish, it was immediately fulfilled. One day, fearing to come home at dawn, he decided to extend the night. He did not dare to stop the Moon, since it was too far away, so he decided to stop the Earth. “...He stood in a commanding pose, extended his hands over the world and solemnly said:

Earth, stop! Stop spinning!
Before he had time to finish these words, the friends were already flying into space at a speed of several dozen miles per minute (464 m/s). Stones, fragments of buildings, metal objects of various kinds rushed around them; Some unfortunate cow was also flying, crashing when it hit the ground. The wind blew with terrible force. The clerk could not even raise his head to look around. Everything around was one picture of destruction..."

Explain what happened from a physics point of view.

II. New topic

You already know that if a body (green ball) is acted upon by another body (red ball), then it changes its speed. They say that the first body worked for the second.
Now let's watch the red ball as it rolls from the chute. It turns out that he also changed his speed. They say that the second body valid on the first.

Definition: The action of bodies on each other is called interaction.

!!! When interacting, both bodies change their speed.

Examples:

• The man jumped from the boat, which means he acquired speed. But the boat also changed its speed - it sailed back.
• When firing from a cannon, both the cannon and the projectile acquire speed: the projectile flies forward, the cannon rolls back.

Let's find out what determines the change in speed of bodies during their interaction ?

Demonstration: a device for studying the law of conservation of momentum.

Experience 1: The balls on the cylinders are the same and their speeds during interaction are also the same (we compare by the distances that the balls have flown).
? Do you think the speeds of the balls will change if one plastic ball is replaced with a steel one? How?
Let's test our hypothesis experimentally.

Experience 2: The balls are different and their speeds during interaction are also different, and the speed of the metal ball less speed of the plastic ball.
They say one body heavier another, more inert(i.e., it strives to maintain its speed longer), one body is more massive than the other, i.e., it has a larger mass.

Definition: Weight is a physical quantity that characterizes the inertia of a body. The greater the mass of a body, the more inert it is.
Every body has mass - a drop of water, a person, the Sun, a speck of dust, etc.
Weight designation – m.
SI units of mass: = 1 kg.
Other units of mass measurement: 1 t = 1000 kg; 1 g = 0.001 kg; 1 mg = 0.000001 kg (see the flyleaf of the textbook).
The mass standard is made of a platinum-iridium alloy, cylindrical in shape, approximately 39 mm high, and stored in the city of Sèvres in France. Copies have been made from the standard: copy No. 12 is kept in Russia, copy No. 20 is kept in the USA.

III. Consolidation

Determine their comparative mass based on the speed of interacting bodies.

Experience 1: Loads of unknown mass are placed on two carts, fastened together by a spring. After cutting the thread, the carts move in different directions at different speeds.

Experience 2: Two balls of different sizes are connected with a thread. After cutting the thread, the balls fly in different directions at different speeds.

Experience 3: In the experiment with the gutter, replace the steel ball with a billiard ball of the same volume. Compare the speeds of the balls after interaction, compare their masses.

Methods for determining body weight:

IV. Lesson summary: What characterizes body weight? How can you determine comparative body weight?

V. Homework:§7 (textbook by S.V. Gromov, N.A. Rodina), think about the question: how can you determine the exact mass of a body if the mass of the body interacting with it is known?

Change in body speed, i.e. the appearance of acceleration is always caused by the influence of any bodies on a given body.

Force is a vector physical quantity that is a measure of the acceleration acquired by bodies during interaction.

The force is characterized by its modulus, point of application and direction.

Force is denoted and measured in Newtons (N). .

If several forces act on a body at the same time, then the resulting force is found by the rule of vector addition.

Newton's laws:

I.(Law of inertia). There are such reference systems (inertial), relative to which translationally moving bodies retain their speed constant if they are not acted upon by other bodies or the action of other bodies is compensated.

II. The product of body mass and acceleration is equal to the sum of all forces acting on the body.

III. The forces with which the bodies act on each other are equal in magnitude and directed in one straight line in opposite directions.

Ticket number 3 1. Body impulse. Law of conservation of momentum. Manifestation of the law of conservation of momentum in nature and its use in technology.

Body impulse is a quantity equal to the product of a body's mass and its speed.

The impulse is indicated by a letter and has the same direction as the speed.

Pulse unit:

The momentum of the body is calculated by the formula: , where

The change in the momentum of the body is equal to the impulse of the force acting on it:

For a closed system of bodies it is true law of conservation of momentum:

in a closed system, the vector sum of the momenta of bodies before interaction is equal to the vector sum of momenta of bodies after interaction.

Ticket number 4

The law of universal gravitation. Gravity. Body weight. Weightlessness.

The forces of mutual attraction acting between any bodies in nature are called forces of universal gravity(or gravitational forces).

Law of Gravity(discovered by Newton):

All bodies are attracted to each other with a force directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between them:

Gravity- this is the force with which the Earth attracts a body located on its surface or near this surface.

Ticket number 5

Transformation of energy during mechanical vibrations, Free and forced vibrations. Resonance.

Oscillations any repetitive movement is called.

Examples: a tree branch in the wind, a pendulum in a clock, a piston in a cylinder of an internal combustion engine, a guitar string, waves on the surface of the sea, etc.

Free are called oscillations that occur after the system is removed from an equilibrium position in the subsequent absence of external influences. These oscillations are damped.

For example, vibrations of a load on a thread.

Forced vibrations that occur under the influence of an external constant periodic force are called. They are unfading.

Examples: a piston in a car engine cylinder, a needle in a sewing machine, a swing if it is constantly swinging.

Ticket number 6

Experimental substantiation of the main provisions of the molecular kinetic theory of the structure of matter. Mass and size of molecules.

Molecular kinetic theory(MCT) is a study of the structure and properties of matter, using ideas about the existence of atoms and molecules as the smallest particles of matter.

MCT is based on three main provisions:

1. All substances consist of tiny particles: atoms and molecules.

2. These particles move randomly.

3. Particles interact with each other.

Ticket number 7

Ideal gas. Basic equation of the molecular kinetic theory of an ideal gas. Temperature and its measurement. Absolute temperature.

Ideal gas is a gas whose interaction between molecules is negligible, because the molecules are far from each other.

Temperature is a macroscopic parameter characterizing the state of thermal equilibrium of a system of bodies: all bodies of the system that are in thermal equilibrium with each other have the same temperature.

Absolute zero- this is the limiting temperature at which the pressure of an ideal gas goes to zero at a fixed volume or the volume of an ideal gas tends to zero at a constant pressure.

Ticket number 8

1. Equation of state of an ideal gas (Mendeleev-Clapeyron equation). Isoprocesses.

State of a given mass of gas is completely determined if its pressure, volume and temperature are known. These quantities are called parameters state of the gas.

Mendeleev-Clapeyron equation

Isoprocesses– these are processes in which one of the macroscopic parameters remains constant, while the other two change.

According to classical physics, in the world we know, bodies and particles constantly interact with each other. Even if we observe objects at rest, this does not mean that nothing is happening. It is thanks to the holding forces between molecules, atoms and elementary particles that you can see an object in the form of matter of the physical world that is accessible and understandable to us.

Interaction of bodies in nature and life

As we know from our own experience, when you fall on something, hit something, collide with something, it turns out to be unpleasant and painful. You push a car or an unwary passer-by crashes into you. In one way or another you interact with the world around you. In physics, this phenomenon was defined as “interaction of bodies.” Let us consider in detail what types modern classical science divides them into.

Types of interaction between bodies

In nature, there are four types of interaction between bodies. The first, well-known, is the gravitational interaction of bodies. The mass of bodies determines how strong gravity is.

It must be large enough for us to notice it. Otherwise, observing and recording this type of interaction is quite difficult. Space is the place where gravitational forces can be observed in the example of cosmic bodies with enormous mass.

Relationship between gravity and body mass

Directly, the energy of interaction between bodies is directly proportional to the mass and inversely proportional to the square of the distance between them. This is according to the definition of modern science.

The attraction of you and all objects on our planet is due to the fact that there is a force of interaction between two bodies with mass. Therefore, an object thrown upward is attracted back to the surface of the Earth. The planet is quite massive, so the force of action is noticeable. Gravity causes the interaction of bodies. The mass of bodies makes it possible to manifest and register it.

The nature of gravity is not clear

The nature of this phenomenon today causes a lot of controversy and speculation; apart from actual observation and the visible relationship between mass and attraction, the force causing gravity has not been identified. Although today a number of experiments are being carried out related to the detection of gravitational waves in outer space. A more accurate assumption was once made by Albert Einstein.

He formulated the hypothesis that gravitational force is a product of the curvature of the fabric of space-time by bodies located in it.

Subsequently, when space is displaced by matter, it tends to restore its volume. Einstein proposed that there is an inverse relationship between force and the density of matter.

An example of a clear demonstration of this dependence is black holes, which have an incredible density of matter and gravity that can attract not only cosmic bodies, but also light.

It is thanks to the influence of the nature of gravity that the force of interaction between bodies ensures the existence of planets, stars and other space objects. In addition, the rotation of some objects around others is present for the same reason.

Electromagnetic forces and progress

The electromagnetic interaction of bodies is somewhat reminiscent of gravitational interaction, but much stronger. The interaction of positively and negatively charged particles is the reason for its existence. Actually, this causes the emergence of an electromagnetic field.

It is generated by the body(s) or absorbed or causes the interaction of charged bodies. This process plays a very important role in the biological activity of a living cell and the redistribution of substances in it.

In addition, a clear example of the electromagnetic manifestation of forces is ordinary electric current, the magnetic field of the planet. Humanity uses this power quite extensively to transmit data. These are mobile communications, television, GPRS and much more.

In mechanics, this manifests itself in the form of elasticity and friction. A clear experiment demonstrating the presence of this force is known to everyone from a school physics course. This is rubbing an ebonite shelf with a silk cloth. Particles with a negative charge that appear on the surface provide attraction for light objects. An everyday example is a comb and hair. After several movements of the plastic through the hair, an attraction arises between them.

It is worth mentioning the compass and the Earth's magnetic field. The arrow is magnetized and has ends with positively and negatively charged particles, as a result, it reacts to the magnetic field of the planet. It turns its “positive” end in the direction of negative particles and vice versa.

Small in size but huge in strength

As for the strong interaction, its specificity is somewhat reminiscent of the electromagnetic type of forces. The reason for this is the presence of positive and negatively charged elements. Like electromagnetic force, the presence of opposite charges leads to the interaction of bodies. The mass of the bodies and the distance between them are very small. This is an area of ​​the subatomic world where such objects are called particles.

These forces act in the region of the atomic nucleus and provide communication between protons, electrons, baryons and other elementary particles. Given their size, compared to large objects, the interaction of charged bodies is much stronger than with the electromagnetic type of force.

Weak forces and radioactivity

The weak type of interaction is directly related to the decay of unstable particles and is accompanied by the release of different types of radiation in the form of alpha, beta and gamma particles. As a rule, substances and materials with similar characteristics are called radioactive.

This type of force is called weak due to the fact that it is weaker than the electromagnetic and strong types of interaction. However, it is more powerful than gravitational interaction. The distances in this process between particles are very small, on the order of 2·10−18 meters.

The fact of discovering force and defining it among the fundamental ones happened quite recently.

With the discovery in 1896 by Henri Becquerel of the phenomenon of radioactivity of substances, in particular uranium salts, the study of this type of interaction of forces began.

Four forces created the universe

The entire Universe exists thanks to four fundamental forces discovered by modern science. They gave birth to space, galaxies, planets, stars and various processes in the form in which we observe it. At this stage, the definition of the fundamental forces in nature is considered complete, but perhaps over time we will learn about the presence of new forces, and knowledge of the nature of the universe will become one step closer to us.

Definition 1

Interaction in physics is the influence of particles or bodies on each other, leading to a change in the state of their motion.

Changing the state of bodies in space

Despite the variety of influences of bodies on each other, in nature there are only four types of fundamental influences:

• gravitational;
• weak interactions;
• strong interactions;
• electromagnetic interactions.

Any changes in nature occur as a result of interaction between bodies. To change the position of the car on the rails, railway workers send a locomotive towards it, which displaces the car from its place and puts it in motion. A sailboat can stand off the coast for a long time until a fair wind blows, which affects its sails. The wheels of a toy car can rotate at any speed, but the toy will not change its position unless a board or ruler is placed under it. The shape or size of the spring can be changed only by hanging a sinker from it or by pulling one of its ends with your hand.

All bodies in nature act on one another or directly through physical fields. If a diesel locomotive acts on a car and changes its speed, then the speed of the diesel locomotive also changes as a result of the reverse action of the car. The Sun acts on the Earth and bodies, keeping it in orbit. But the Earth also attracts the Sun, and in turn changes its trajectory. So, in all cases we can only talk about the mutual action of bodies - interaction.

When interacting, the speeds of bodies or their parts change. On the other hand, interacting with different bodies, it will change its speed differently. Thus, a sailboat can gain speed due to the action of the wind on it. But the same result can be achieved by turning on the engine located on the sailboat. It can also be moved from its place by a boat acting on a sailboat through a cable. In order not to name every time all interacting bodies, or bodies that act on a given one, all these actions are united by one concept of force.

What is strength?

Force, perceiving it as a physical concept, can be greater or less, and also taking into account the changes it causes in the state of the body or its parts.

Definition 2

Force is a physical quantity that is characterized as the action of one body on another.

The action of a diesel locomotive on a car will be much more intense than the action of several loaders. Under the influence of the diesel locomotive, the car will move faster and begin to move at a higher speed than when the car is pushed by loaders, who will slightly move the car or not move it at all.

In order to make mathematical calculations, force is denoted by the Latin letter $F$.

Like all other physical quantities, force has certain units. Nowadays science uses a unit called the newton ($H$). It received this name in honor of the scientist Isaac Newton, who made significant contributions to the development of physical and mathematical science.

I. Newton is an outstanding English scientist, the founder of classical physics. His scientific works concern mechanics, optics, astronomy and mathematics. He formulated the laws of classical mechanics, discovered the dispersion of light, developed differential and integral calculus, etc.

Force measurement

To measure force, special devices called dynamometers are used. It is worth noting that indicating the numerical value of a force is not always sufficient to determine the data of its action. You need to know the point of its application and the direction of action.

If a tall block that stands on a table is pushed at the bottom, it will slide on the surface of the table. If you apply force to it in its upper part, it will simply tip over.

It is clear that the direction in which the block falls depends on the direction in which we push it. So force is also direction. The direction of the force determines the change in the speed of the body on which this force acts.

Using the graphical method, you can carry out various mathematical operations with forces. Thus, if at one point on the body the applied forces $2H$ and $CH$ act in the same direction, then their action can be replaced by one force that works in the same direction, and its value is equal to the sum of the values ​​of each of the forces. The vector of this force has a length that is equal to the sum of the lengths of both vectors.

A resultant force is a force whose action acts equally on several forces applied to a body at a certain point.

Another case is possible when forces applied at one point of the body act directly at opposite points. In this case, they can be replaced by one force moving in the direction of the larger force, and its value is equal to the difference between the values ​​of each force. The length of the vector of this force is equal to the difference in the length of the vectors of the applied forces.

Inertia is the phenomenon of bodies maintaining a constant speed when they are not acted upon by other bodies. This phenomenon consists in the fact that it takes a certain time to change the speed of a body. Inertia cannot be measured, it can only be observed or reproduced.

Let us note that in earthly conditions it is impossible to create circumstances in which no forces act on the body, because there is always gravity, motor resistance forces, and the like. The phenomenon of inertia was discovered by the famous scientist Galileo Galilei. It is worth noting that various scales are used to directly measure mass. Among them, the most common and simplest are lever ones. On these scales, the interaction with the Earth of the body and the standard weights placed on the scales is compared. In practice, other scales are used that are adapted to different operating conditions and have different designs. In this case, the accuracy of mass measurement is of great importance.