Weight. Full lessons - Knowledge Hypermarket. Phone interaction. Strength. Newton's second law What changes when bodies interact

08.12.2020

Phone interaction. 2. Types of interaction. 3. Strength. 4. Forces in mechanics.

Simple observations and experiments, for example with carts (Fig. 3), lead to the following qualitative conclusions: a) a body on which other bodies do not act keeps its speed unchanged;

b) the acceleration of the body occurs under the action of other bodies, but also depends on the body itself; c) the actions of bodies on each other always have the character of interaction. These conclusions are confirmed when observing phenomena in nature, technology, outer space only in inertial frames of reference.

Interactions differ from each other both quantitatively and qualitatively. For example, it is clear that the more the spring is deformed, the greater the interaction of its coils. Or, the closer two charges of the same name are, the stronger they will be attracted. In the simplest cases of interaction, the quantitative characteristic is force. Force - the reason for the acceleration of bodies with respect to the inertial reference frame or their deformation. Strength is

vector physical quantity, which is a measure of the acceleration acquired by bodies in the course of interaction. Force is characterized by: a) module; b) application point; c) direction.

The unit of force is newton. 1 newton is the force that imparts an acceleration of 1 m / s to a body of mass 1 kg in the direction of this force, if no other bodies act on it. The resultant of several forces is a force whose action is equivalent to the action of the forces that it replaces. The resultant is the vector sum of all forces applied to the body.

R=F1+F2+...+Fn,.

Interactions are also qualitatively different in their properties. For example, electrical and magnetic interactions are associated with the presence of charges on particles or with the movement of charged particles. The easiest way to calculate forces in electrodynamics: the Ampère force - F = IlBsina, Lorentz force - F= qv Bsin a., Coulomb force - F=q 1 q 2 / r 2 ; and gravitational forces: the law of universal gravitation- F=gm 1 m 2 / r 2 . Mechanical forces like

elastic force and friction force, arise as a result of electromagnetic interaction. For their calculation it is necessary to use formulas: .Fynp = - kx(Hooke's law), Ftr = MN - friction force.

Newton's laws were formulated on the basis of experimental data. Newton's second law. The acceleration with which a body moves is directly proportional to the resultant of all forces acting on the body, inversely proportional to its mass and is directed in the same way as the resultant force: a = F/ m.

To solve problems, the law is often written in the form: F= that.

The third law is a generalization and sounds like this: Bodies act on each other with forces equal in magnitude and opposite in direction.

The first law: there are such frames of reference, relative to which a progressively moving body keeps its speed constant if no other bodies act on it (or the action of other bodies is compensated).

Question 4

Inertial frames of reference

Inertial reference systems. Newton's first law

Question 3

Newton's first law- (the law of inertia) there are such frames of reference with respect to which the translationally moving body, while maintaining the speed, is unchanged or rests or moves in a straight line and uniformly, if external bodies do not act on it or their action equal to zero, that is, is compensated.

A reference system in which the law of inertia is valid: a material point, when no forces act on it (or mutually balanced forces act), is at rest or uniform rectilinear motion. Any frame of reference moving with respect to the IS. about. progressively, evenly and rectilinearly, there is also I. s. about. Therefore, theoretically, there can be any number of equal I. s. o., possessing the important property that the laws of physics are the same in all such systems (the so-called principle of relativity).

Phone interaction. The reason for changing the speed of a body is always its interaction with other bodies.

After turning off the engine, the car gradually slows down and stops. The main reason for changing the speed of a car is the interaction of its wheels with the road surface.

A ball lying motionless on the ground never moves by itself. The speed of the ball changes only as a result of the action of other bodies on it, for example, the feet of a football player.

Constancy of the ratio of acceleration modules. When two bodies interact, the speeds of both the first and second bodies always change, i.e., both bodies acquire accelerations. The acceleration modules of two interacting bodies may be different, but their ratio is constant for any interaction:

Interactions differ from each other both quantitatively and qualitatively. For example, it is clear that the more the spring is deformed, the greater the interaction of its coils. Or the closer two charges of the same name are, the stronger they will be attracted. In the simplest cases of interaction, the quantitative characteristic is strength.

Body mass. The property of a body that determines its acceleration when interacting with other bodies is called inertia.

A quantitative measure of the inertia of the body is the mass of the body. The more mass a body has, the less acceleration it receives during interaction.

Therefore, it is accepted in physics that the ratio of the masses of the interacting bodies is equal to the inverse ratio of the acceleration modules:

The unit of mass in the International System is the mass of a special standard made of an alloy of platinum and iridium. The mass of this standard is called kilogram(kg).

The mass of any body can be found by carrying out the interaction of this body with the standard mass.

By definition of the concept of mass, the ratio of the masses of interacting bodies is equal to the inverse ratio of the modules of their accelerations (5.2). By measuring the acceleration modules of the body and the standard, we can find the ratio of the body mass to the mass of the standard:

The ratio of the mass of the body to the mass of the standard is equal to the ratio of the acceleration module of the standard to the acceleration module of the body during their interaction.

The mass of the body can be expressed in terms of the mass of the reference:

The mass of a body is a physical quantity that characterizes its inertia.

Force is the reason for the acceleration of bodies with respect to the inertial reference frame or their deformation. Force is a vector physical quantity, which is a measure of the acceleration acquired by bodies during interaction. Force is characterized by: a) module; b) application point; c) direction.

Newton's second law - the force acting on a body is equal to the product of the body's mass and the acceleration reported by this force.

Definition 1

Interaction in physics is the impact 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:

gravity;
weak interactions;
strong interactions;
electromagnetic interactions.

Any changes in nature occur as a result of the interaction between bodies. To change the position of a wagon on the rails, the railroad sends a locomotive to it, which displaces the wagon from its place and puts it into motion. A sailboat can stand near the shore for a long time until a fair wind blows, which will affect its sails. The wheels of a toy car can rotate at any speed, but the toy will not change its position unless a plank 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 one on another or directly through physical fields. If the diesel locomotive acts on the 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 in different ways. So, 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 by a boat acting on a sailboat through a cable. In order not to name each time all interacting bodies, or bodies that act on a given it, all these actions unite the concept of force.

What is strength?

Force, perceiving it as a physical concept, can be greater or lesser, and also taking into account the changes caused by it 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 the diesel locomotive on the wagon will be much more intense than the action of several loaders. Under the action 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 slightly shift the car or not move at all.

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

Like all other physical quantities, force has certain units. Today, science uses a unit called the newton ($H$). It got its name in honor of the scientist Isaac Newton, who made a significant contribution 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, and so on.

Force measurement

To measure force, special devices are used, which are called dynamometers. It should be noted that specifying the numerical value of the 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, then it will simply tip over.

It is clear that the direction of the fall of the bar depends on the direction in which we will push it. So strength is also direction. The change in the speed of the body on which this force acts depends on the direction of the force.

Using the graphical method, it is possible to carry out various mathematical operations with forces. So, 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 equal to the sum of the lengths of both vectors.

The 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 the forces applied at one point of the body act directly in opposite ones. 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 in 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 no other bodies act on them. This phenomenon consists in the fact that it takes a certain time to change the speed of the body. Inertia cannot be measured, it can only be observed or reproduced.

Let us note that under terrestrial conditions it is impossible to create circumstances under which forces do not act on the body, because there is always terrestrial attraction, the force of resistance is motive, and the like. The phenomenon of inertia was discovered by the famous scientist Galileo Galilei. It is worth noting that various scales are used for direct measurement of mass. Among them, the most common and simplest are lever ones. On these scales, the interaction with the Earth of the body and reference weights placed on the scales is compared. In practice, other scales are also used, which are adapted to different working conditions and have different designs. In this case, the accuracy of mass measurement is of great importance.

What is the reason for the movement of bodies? The answer to this question is given by the branch of mechanics called dynamics.
How can you change the speed of a body, make it move faster or slower? Only when interacting with other bodies. When interacting, bodies can change not only the speed, but also the direction of movement and deform, while changing the shape and volume. In dynamics, for a quantitative measure of the interaction of bodies on each other, a quantity called force is introduced. And the change in speed during the action of the force is characterized by acceleration. Force is the cause of acceleration.

The concept of strength

Force is a vector physical quantity that characterizes the action of one body on another, manifested in the deformation of the body or a change in its movement relative to other bodies.

Force is denoted by the letter F. The unit of measure in the SI system is Newton (N), which is equal to the force under the influence of which a body weighing one kilogram receives an acceleration of one meter per second squared. The force F is completely determined if its modulus, direction in space, and point of application are given.
To measure forces, a special device called a dynamometer is used.

How many forces are there in nature?

Forces can be divided into two types:

They act with direct interaction, contact (elastic forces, friction forces);
They act at a distance, long-range (attraction, gravity, magnetic, electric).

In direct interaction, for example, a shot from a toy gun, the bodies experience a change in shape and volume compared to the original state, that is, deformation of compression, stretching, bending. The pistol spring is compressed before firing, the bullet is deformed when it hits the spring. In this case, the forces act at the moment of deformation and disappear along with it. Such forces are called elastic. Friction forces arise from the direct interaction of bodies, when they roll, slide relative to each other.

An example of forces acting at a distance is a stone thrown up, due to gravity, it will fall to the Earth, ebbs and flows that occur on ocean coasts. As the distance increases, these forces decrease.
Depending on the physical nature of the interaction, forces can be divided into four groups:

weak;
strong;
gravity;
electromagnetic.

We encounter all types of these forces in nature.
Gravitational or gravity forces are the most universal, anything that has mass is capable of experiencing these interactions. They are omnipresent and all-pervading, but very weak, so we do not notice them, especially at great distances. Gravitational forces are long-range, binding all bodies in the Universe.

Electromagnetic interactions occur between charged bodies or particles, through the action of an electromagnetic field. Electromagnetic forces allow us to see objects, since light is one of the forms of electromagnetic interactions.

Weak and strong interactions became known through the study of the structure of the atom and the atomic nucleus. Strong interactions occur between particles in nuclei. Weak ones characterize the mutual transformations of elementary particles into each other, act in thermonuclear fusion reactions and radioactive decays of nuclei.

What if several forces act on the body?

When several forces act on a body, this action is simultaneously replaced by one force equal to their geometric sum. The force obtained in this case is called the resultant force. It imparts the same acceleration to the body as the forces simultaneously acting on the body. This is the so-called principle of superposition of forces.

According to classical physics, in the world we know, there is a constant interaction of bodies, particles with each other. Even if we observe objects that are 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 an accessible and understandable matter of the physical world.

The interaction of bodies in nature and life

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

Types of body interaction

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

It must be large enough for us to notice. Otherwise, the observation and registration of this type of interaction is quite difficult. Space is the place where it is quite possible to observe the forces of gravity on the example of cosmic bodies with a huge mass.

Relationship between gravity and body mass

Directly the interaction energy of 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 that have mass. Therefore, an object thrown up is attracted back to the surface of the Earth. The planet is quite massive, so the force of action is palpable. Gravity causes bodies to interact. 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 assumptions, in addition to actual observation and the apparent relationship between mass and attraction, the force that causes gravity has not been identified. Although today there are a number of experiments 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 the gravitational force is a product of the curvature of the fabric of space-time by the bodies located in it.

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

An example of a visual demonstration of this dependence can be black holes, which have an unthinkable 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, 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 (bodies) 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 an ordinary electric current, the magnetic field of the planet. Mankind makes extensive use of this power to transmit data. These are mobile communications, television, GPRS and much more.

In mechanics, this manifests itself in the form of elasticity, friction. A visual 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. The particles with a negative charge that have arisen 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. Turns its "positive" end in the direction of negative particles and vice versa.

Small in size but great in power

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

These forces act in the region of the atomic nucleus and provide a connection between protons, electrons, baryons and other elementary particles. Against the background of their size, in comparison with large objects, the interaction of charged bodies is much stronger than with the electromagnetic type of forces.

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 various 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 type of interaction. However, it is more powerful than the gravitational interaction. The distances in this process between the particles are very small, about 2·10 −18 meters.

The fact of the discovery of force and its definition in a number of 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 rise to space, galaxies, planets, stars and various processes in the form in which we observe it. At this stage, the definition of 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.