Obi-Wan Kenobi said that strength holds the galaxy together. The same can be said about gravity. The fact is that gravity allows us to walk on the Earth, the Earth to revolve around the Sun, and the Sun to revolve around the supermassive black hole at the center of our galaxy. How to understand gravity? About this - in our article.

Let's say right away that you will not find here an unambiguously correct answer to the question "What is gravity." Because it just doesn't exist! Gravity is one of the most mysterious phenomena that scientists puzzle over and still cannot fully explain its nature.

There are many hypotheses and opinions. There are more than a dozen theories of gravity, alternative and classical. We will consider the most interesting, relevant and modern.

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Gravity is a physical fundamental interaction

There are 4 fundamental interactions in physics. Thanks to them, the world is exactly the way it is. Gravity is one of these forces.

Fundamental Interactions:

• gravity;
• electromagnetism;
• strong interaction;
• weak interaction.

Gravity is the weakest of the four fundamental forces.

At the moment, the current theory describing gravity is GR (general relativity). It was proposed by Albert Einstein in 1915-1916.

However, we know that it is too early to talk about the ultimate truth. After all, several centuries before the advent of general relativity in physics, Newtonian theory, which was significantly expanded, dominated to describe gravity.

At the moment, it is impossible to explain and describe all issues related to gravity within the framework of general relativity.

Before Newton, it was widely believed that gravity on earth and celestial gravity were different things. It was believed that the planets move according to their own, different from earthly, ideal laws.

Newton discovered the law of universal gravitation in 1667. Of course, this law existed even during the dinosaurs and much earlier.

Ancient philosophers thought about the existence of gravity. Galileo experimentally calculated the acceleration of free fall on Earth, discovering that it is the same for bodies of any mass. Kepler studied the laws of motion of celestial bodies.

Newton was able to formulate and generalize the results of observations. Here's what he got:

Two bodies are attracted to each other with a force called gravitational force or gravitational force.

The formula for the force of attraction between bodies is:

G is the gravitational constant, m is the mass of the bodies, r is the distance between the centers of mass of the bodies.

What is the physical meaning of the gravitational constant? It is equal to the force with which bodies with masses of 1 kilogram each act on each other, being at a distance of 1 meter from each other.

According to Newton's theory, every object creates a gravitational field. The accuracy of Newton's law has been tested at distances of less than one centimeter. Of course, for small masses these forces are insignificant and can be neglected.

Newton's formula is applicable both for calculating the force of attraction of planets to the sun, and for small objects. We simply do not notice the force with which, say, the balls on the billiard table are attracted. Nevertheless, this force exists and can be calculated.

The force of attraction acts between any bodies in the universe. Its effect extends to any distance.

Newton's law of universal gravitation does not explain the nature of the force of attraction, but establishes quantitative patterns. Newton's theory does not contradict general relativity. It is quite sufficient for solving practical problems on the scale of the Earth and for calculating the motion of celestial bodies.

Gravity in General Relativity

Despite the fact that Newton's theory is quite applicable in practice, it has a number of shortcomings. The law of universal gravitation is a mathematical description, but does not give an idea of ​​the fundamental physical nature of things.

According to Newton, the force of attraction acts at any distance. And it works instantly. Considering that the fastest speed in the world is the speed of light, there is a discrepancy. How can gravity act instantaneously at any distance, when light needs not an instant, but several seconds or even years to overcome them?

Within the framework of general relativity, gravity is considered not as a force that acts on bodies, but as a curvature of space and time under the influence of mass. Thus, gravity is not a force interaction.

What is the effect of gravity? Let's try to describe it using an analogy.

Imagine space as an elastic sheet. If you put a light tennis ball on it, the surface will remain flat. But if you put a heavy weight next to the ball, it will push a hole in the surface, and the ball will begin to roll towards the large and heavy weight. This is "gravity".

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Discovery of gravitational waves

Gravitational waves were predicted by Albert Einstein back in 1916, but they were only discovered a hundred years later, in 2015.

What are gravitational waves? Let's draw an analogy again. If you throw a stone into calm water, circles will go on the surface of the water from the place of its fall. Gravitational waves are the same ripples, perturbations. Only not on the water, but in the world space-time.

Instead of water - space-time, and instead of stone, say, a black hole. Any accelerated movement of mass generates a gravitational wave. If the bodies are in a state of free fall, the distance between them will change when a gravitational wave passes.

Since gravity is a very weak force, the detection of gravitational waves has been associated with great technical difficulties. Modern technologies have made it possible to detect a burst of gravitational waves only from supermassive sources.

A suitable event for registering a gravitational wave is the merger of black holes. Unfortunately or fortunately, this happens quite rarely. Nevertheless, scientists managed to register a wave that literally rolled through the space of the Universe.

To register gravitational waves, a detector with a diameter of 4 kilometers was built. During the passage of the wave, oscillations of mirrors on suspensions in vacuum and the interference of light reflected from them were recorded.

Gravitational waves confirmed the validity of general relativity.

Gravity and elementary particles

In the standard model, certain elementary particles are responsible for each interaction. We can say that particles are carriers of interactions.

The graviton is responsible for gravity - a hypothetical massless particle with energy. By the way, in our separate material, read more about the Higgs boson and other elementary particles that made a lot of noise.

Finally, here are some interesting facts about gravity.

10 facts about gravity

1. To overcome the force of gravity of the Earth, the body must have a speed equal to 7.91 km / s. This is the first cosmic speed. It is enough for a body (for example, a space probe) to move in orbit around the planet.
2. To escape the Earth's gravitational field, a spacecraft must have a speed of at least 11.2 km/s. This is the second space velocity.
3. Objects with the strongest gravity are black holes. Their gravity is so strong that they even attract light (photons).
4. You will not find the force of gravity in any equation of quantum mechanics. The fact is that when you try to include gravity in the equations, they lose their relevance. This is one of the most important problems in modern physics.
5. The word gravity comes from the Latin “gravis”, which means “heavy”.
6. The more massive the object, the stronger the gravity. If a person who weighs 60 kilograms on Earth weighs on Jupiter, the scales will show 142 kilograms.
7. NASA scientists are trying to develop a gravitational beam that will allow objects to be moved contactlessly, overcoming the force of gravity.
8. Astronauts in orbit also experience gravity. More specifically, microgravity. They seem to fall endlessly along with the ship in which they are.
9. Gravity always attracts and never repels.
10. A tennis ball-sized black hole pulls objects with the same force as our planet.

Now you know the definition of gravity and you can say what formula is used to calculate the force of attraction. If the granite of science is holding you down harder than gravity, contact our student service. We will help you learn easily under the heaviest workloads!

Since ancient times, mankind has thought about how the world around us works. Why does grass grow, why does the Sun shine, why can't we fly... The latter, by the way, has always been of particular interest to people. Now we know that the reason for everything is gravity. What it is, and why this phenomenon is so important on the scale of the Universe, we will consider today.

Introduction

Scientists have found that all massive bodies experience mutual attraction to each other. Subsequently, it turned out that this mysterious force also determines the movement of celestial bodies in their constant orbits. The very same theory of gravity was formulated by a genius whose hypotheses predetermined the development of physics for many centuries to come. Developed and continued (albeit in a completely different direction) this teaching was Albert Einstein - one of the greatest minds of the past century.

For centuries, scientists have observed gravity, trying to understand and measure it. Finally, in the last few decades, even such a phenomenon as gravity has been put at the service of mankind (in a certain sense, of course). What is it, what is the definition of the term in question in modern science?

scientific definition

If you study the works of ancient thinkers, you can find out that the Latin word "gravitas" means "gravity", "attraction". Today, scientists so call the universal and constant interaction between material bodies. If this force is relatively weak and acts only on objects that move much more slowly, then Newton's theory is applicable to them. If the opposite is the case, Einstein's conclusions should be used.

Let's make a reservation right away: at present, the very nature of gravity itself has not been fully studied in principle. What it is, we still do not fully understand.

Theories of Newton and Einstein

According to the classical teaching of Isaac Newton, all bodies are attracted to each other with a force that is directly proportional to their mass, inversely proportional to the square of the distance that lies between them. Einstein, on the other hand, argued that gravity between objects manifests itself in the case of curvature of space and time (and the curvature of space is possible only if there is matter in it).

This idea was very deep, but modern research proves it to be somewhat inaccurate. Today it is believed that gravity in space only bends space: time can be slowed down and even stopped, but the reality of changing the shape of temporary matter has not been theoretically confirmed. Therefore, the classical Einstein equation does not even provide for a chance that space will continue to influence matter and the emerging magnetic field.

To a greater extent, the law of gravity (universal gravitation) is known, the mathematical expression of which belongs precisely to Newton:

\[ F = γ \frac[-1.2](m_1 m_2)(r^2) \]

Under γ is understood the gravitational constant (sometimes the symbol G is used), the value of which is 6.67545 × 10−11 m³ / (kg s²).

Interaction between elementary particles

The incredible complexity of the space around us is largely due to the infinite number of elementary particles. There are also various interactions between them at levels that we can only guess at. However, all types of interaction of elementary particles among themselves differ significantly in their strength.

The most powerful of all the forces known to us bind together the components of the atomic nucleus. To separate them, you need to spend a truly colossal amount of energy. As for electrons, they are “tied” to the nucleus only by ordinary ones. To stop it, sometimes the energy that appears as a result of the most ordinary chemical reaction is enough. Gravity (what it is, you already know) in the variant of atoms and subatomic particles is the easiest kind of interaction.

The gravitational field in this case is so weak that it is difficult to imagine. Oddly enough, but it is they who “follow” the movement of celestial bodies, whose mass is sometimes impossible to imagine. All this is possible due to two features of gravity, which are especially pronounced in the case of large physical bodies:

• Unlike atomic ones, it is more noticeable at a distance from the object. So, the Earth's gravity keeps even the Moon in its field, and the similar force of Jupiter easily supports the orbits of several satellites at once, the mass of each of which is quite comparable to the Earth's!
• In addition, it always provides attraction between objects, and with distance this force weakens at a low speed.

The formation of a more or less harmonious theory of gravitation occurred relatively recently, and precisely on the basis of the results of centuries-old observations of the motion of planets and other celestial bodies. The task was greatly facilitated by the fact that they all move in a vacuum, where there are simply no other possible interactions. Galileo and Kepler, two outstanding astronomers of the time, helped pave the way for new discoveries with their most valuable observations.

But only the great Isaac Newton was able to create the first theory of gravity and express it in a mathematical representation. This was the first law of gravity, the mathematical representation of which is presented above.

Conclusions of Newton and some of his predecessors

Unlike other physical phenomena that exist in the world around us, gravity manifests itself always and everywhere. You need to understand that the term "zero gravity", which is often found in pseudo-scientific circles, is extremely incorrect: even weightlessness in space does not mean that a person or a spacecraft is not affected by the attraction of some massive object.

In addition, all material bodies have a certain mass, expressed in the form of a force that was applied to them, and an acceleration obtained due to this impact.

Thus, gravitational forces are proportional to the mass of objects. Numerically, they can be expressed by obtaining the product of the masses of both considered bodies. This force strictly obeys the inverse dependence on the square of the distance between objects. All other interactions depend quite differently on the distances between two bodies.

Mass as the cornerstone of theory

The mass of objects has become a particular point of contention around which Einstein's entire modern theory of gravity and relativity is built. If you remember the Second, then you probably know that mass is a mandatory characteristic of any physical material body. It shows how an object will behave if force is applied to it, regardless of its origin.

Since all bodies (according to Newton) accelerate when an external force acts on them, it is the mass that determines how large this acceleration will be. Let's look at a clearer example. Imagine a scooter and a bus: if you apply exactly the same force to them, they will reach different speeds in different times. All this is explained by the theory of gravity.

What is the relationship between mass and attraction?

If we talk about gravity, then the mass in this phenomenon plays a role completely opposite to that which it plays in relation to the force and acceleration of an object. It is she who is the primary source of attraction itself. If you take two bodies and see with what force they attract a third object, which is located at equal distances from the first two, then the ratio of all forces will be equal to the ratio of the masses of the first two objects. Thus, the force of attraction is directly proportional to the mass of the body.

If we consider Newton's Third Law, we can see that he says exactly the same thing. The force of gravity, which acts on two bodies located at an equal distance from the source of attraction, directly depends on the mass of these objects. In everyday life, we talk about the force with which a body is attracted to the surface of the planet as its weight.

Let's sum up some results. So, mass is closely related to acceleration. At the same time, it is she who determines the force with which gravity will act on the body.

Features of acceleration of bodies in a gravitational field

This amazing duality is the reason why, in the same gravitational field, the acceleration of completely different objects will be equal. Suppose we have two bodies. Let's assign a mass z to one of them, and Z to the other. Both objects are dropped to the ground, where they fall freely.

How is the ratio of forces of attraction determined? It is shown by the simplest mathematical formula - z / Z. That's just the acceleration they receive as a result of the force of gravity, will be exactly the same. Simply put, the acceleration that a body has in a gravitational field does not depend in any way on its properties.

What does the acceleration depend on in the described case?

It depends only (!) on the mass of objects that create this field, as well as on their spatial position. The dual role of mass and the equal acceleration of various bodies in a gravitational field have been discovered for a relatively long time. These phenomena have received the following name: "Principle of equivalence". This term once again emphasizes that acceleration and inertia are often equivalent (to a certain extent, of course).

On the importance of G

From the school physics course, we remember that the acceleration of free fall on the surface of our planet (Earth's gravity) is 10 m / s² (9.8 of course, but this value is used for ease of calculation). Thus, if air resistance is not taken into account (at a significant height with a small fall distance), then the effect will be obtained when the body acquires an acceleration increment of 10 m / s. every second. Thus, a book that has fallen from the second floor of a house will move at a speed of 30-40 m/sec by the end of its flight. Simply put, 10 m/s is the "speed" of gravity within the Earth.

Acceleration due to gravity in the physical literature is denoted by the letter "g". Since the shape of the Earth is to a certain extent more like a tangerine than a sphere, the value of this quantity is far from being the same in all its regions. So, at the poles, the acceleration is higher, and on the tops of high mountains it becomes less.

Even in the mining industry, gravity plays an important role. The physics of this phenomenon sometimes saves a lot of time. Thus, geologists are especially interested in the ideally accurate determination of g, since this allows exploration and finding of mineral deposits with exceptional accuracy. By the way, what does the gravity formula look like, in which the value we have considered plays an important role? Here she is:

Note! In this case, the gravitational formula means by G the "gravitational constant", the value of which we have already given above.

At one time, Newton formulated the above principles. He perfectly understood both unity and universality, but he could not describe all aspects of this phenomenon. This honor fell to Albert Einstein, who was also able to explain the principle of equivalence. It is to him that mankind owes a modern understanding of the very nature of the space-time continuum.

Theory of relativity, works of Albert Einstein

At the time of Isaac Newton, it was believed that reference points can be represented as some kind of rigid "rods", with the help of which the position of the body in the spatial coordinate system is established. At the same time, it was assumed that all observers who mark these coordinates would be in a single time space. In those years, this provision was considered so obvious that no attempts were made to challenge or supplement it. And this is understandable, because within our planet there are no deviations in this rule.

Einstein proved that the accuracy of the measurement would be really significant if the hypothetical clock was moving much slower than the speed of light. Simply put, if one observer, moving slower than the speed of light, follows two events, then they will happen for him at the same time. Accordingly, for the second observer? the speed of which is the same or more, events can occur at different times.

But how is the force of gravity related to the theory of relativity? Let's explore this issue in detail.

Relationship between relativity and gravitational forces

In recent years, a huge number of discoveries in the field of subatomic particles have been made. The conviction is growing stronger that we are about to find the final particle, beyond which our world cannot be divided. The more insistent is the need to find out exactly how the smallest “bricks” of our universe are affected by those fundamental forces that were discovered in the last century, or even earlier. It is especially disappointing that the very nature of gravity has not yet been explained.

That is why, after Einstein, who established the “incapacity” of classical Newtonian mechanics in the area under consideration, researchers focused on a complete rethinking of the data obtained earlier. In many ways, gravity itself has undergone a revision. What is it at the level of subatomic particles? Does it have any meaning in this amazing multidimensional world?

A simple solution?

At first, many assumed that the discrepancy between Newton's gravity and the theory of relativity can be explained quite simply by drawing analogies from the field of electrodynamics. It could be assumed that the gravitational field propagates like a magnetic one, after which it can be declared a "mediator" in the interactions of celestial bodies, explaining many inconsistencies between the old and the new theory. The fact is that then the relative velocities of propagation of the forces under consideration would be much lower than the speed of light. So how are gravity and time related?

In principle, Einstein himself almost succeeded in constructing a relativistic theory on the basis of just such views, only one circumstance prevented his intention. None of the scientists of that time had any information at all that could help determine the "speed" of gravity. But there was a lot of information related to the movements of large masses. As you know, they were just the generally recognized source of powerful gravitational fields.

High speeds strongly affect the masses of bodies, and this is not at all like the interaction of speed and charge. The higher the speed, the greater the mass of the body. The problem is that the last value would automatically become infinite in the case of movement at the speed of light or higher. Therefore, Einstein concluded that there is not a gravitational, but a tensor field, for the description of which many more variables should be used.

His followers came to the conclusion that gravity and time are practically unrelated. The fact is that this tensor field itself can act on space, but it is not able to influence time. However, the brilliant modern physicist Stephen Hawking has a different point of view. But that's a completely different story...

Gravitational force is the force with which bodies of a certain mass are attracted to each other, located at a certain distance from each other.

The English scientist Isaac Newton in 1867 discovered the law of universal gravitation. This is one of the fundamental laws of mechanics. The essence of this law is as follows:any two material particles are attracted to each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

The force of attraction is the first force that a person felt. This is the force with which the Earth acts on all bodies located on its surface. And any person feels this force as his own weight.

Law of gravity

There is a legend that Newton discovered the law of universal gravitation quite by accident, walking in the evening in the garden of his parents. Creative people are constantly in search, and scientific discoveries are not instantaneous insight, but the fruit of long-term mental work. Sitting under an apple tree, Newton was thinking about another idea, and suddenly an apple fell on his head. It was clear to Newton that the apple fell as a result of the Earth's gravity. “But why doesn’t the moon fall to the Earth? he thought. “It means that some other force is acting on it, keeping it in orbit.” This is how the famous law of gravity.

Scientists who had previously studied the rotation of celestial bodies believed that celestial bodies obey some completely different laws. That is, it was assumed that there are completely different laws of attraction on the surface of the Earth and in space.

Newton combined these supposed kinds of gravity. Analyzing Kepler's laws describing the motion of the planets, he came to the conclusion that the force of attraction arises between any bodies. That is, both the apple that fell in the garden and the planets in space are affected by forces that obey the same law - the law of universal gravitation.

Newton found that Kepler's laws only work if there is an attractive force between the planets. And this force is directly proportional to the masses of the planets and inversely proportional to the square of the distance between them.

The force of attraction is calculated by the formula F=G m 1 m 2 / r 2

m 1 is the mass of the first body;

m2is the mass of the second body;

r is the distance between the bodies;

G is the coefficient of proportionality, which is called gravitational constant or gravitational constant.

Its value was determined experimentally. G\u003d 6.67 10 -11 Nm 2 / kg 2

If two material points with a mass equal to a unit of mass are at a distance equal to a unit of distance, then they are attracted with a force equal to G.

The forces of attraction are the gravitational forces. They are also called gravity. They are subject to the law of universal gravitation and appear everywhere, since all bodies have mass.

Gravity

The gravitational force near the surface of the Earth is the force with which all bodies are attracted to the Earth. They call her gravity. It is considered constant if the distance of the body from the Earth's surface is small compared to the radius of the Earth.

Since gravity, which is the gravitational force, depends on the mass and radius of the planet, it will be different on different planets. Since the radius of the Moon is less than the radius of the Earth, then the force of attraction on the Moon is less than on the Earth by 6 times. And on Jupiter, on the contrary, gravity is 2.4 times greater than gravity on Earth. But body weight remains constant, no matter where it is measured.

Many people confuse the meaning of weight and gravity, believing that gravity is always equal to weight. But it's not.

The force with which the body presses on the support or stretches the suspension, this is the weight. If the support or suspension is removed, the body will begin to fall with the acceleration of free fall under the action of gravity. The force of gravity is proportional to the mass of the body. It is calculated according to the formulaF= m g , where m- body mass, g- acceleration of gravity.

Body weight can change, and sometimes disappear altogether. Imagine that we are in an elevator on the top floor. The elevator is worth it. At this moment, our weight P and the force of gravity F, with which the Earth pulls us, are equal. But as soon as the elevator began to move down with acceleration a , weight and gravity are no longer equal. According to Newton's second lawmg+ P = ma . P \u003d m g -ma.

It can be seen from the formula that our weight decreased as we moved down.

At the moment when the elevator picked up speed and began to move without acceleration, our weight is again equal to gravity. And when the elevator began to slow down its movement, acceleration a became negative and the weight increased. There is an overload.

And if the body moves down with the acceleration of free fall, then the weight will completely become equal to zero.

At a=g R=mg-ma= mg - mg=0

This is a state of weightlessness.

So, without exception, all material bodies in the Universe obey the law of universal gravitation. And the planets around the Sun, and all the bodies that are near the surface of the Earth.

Every person in his life has come across this concept more than once, because gravity is the basis of not only modern physics, but also a number of other related sciences.

Many scientists have been studying the attraction of bodies since ancient times, but the main discovery is attributed to Newton and is described as a story known to everyone with a fruit that fell on his head.

What is gravity in simple words

Gravity is the attraction between several objects throughout the universe. The nature of the phenomenon is different, as it is determined by the mass of each of them and the length between, that is, the distance.

Newton's theory was based on the fact that both the falling fruit and the satellite of our planet are affected by the same force - attraction to the Earth. And the satellite did not fall on the earth space precisely because of its mass and distance.

Gravity field

The gravitational field is a space within which bodies interact according to the laws of attraction.

Einstein's theory of relativity describes the field as a certain property of time and space, which is characteristically manifested when physical objects appear.

gravity wave

This is a certain kind of change in the fields that are formed as a result of radiation from moving objects. They break away from the subject and propagate in a wave effect.

Theories of gravity

The classical theory is Newtonian. However, it was not perfect and alternative options subsequently appeared.

These include:

• metric theories;
• non-metric;
• vector;
• Le Sage, who first described the phases;
• quantum gravity.

Today, there are several dozen different theories, all of which either complement each other or consider phenomena from the other side.

Its useful to note: there is no perfect solution yet, but ongoing developments are opening up more answers regarding the attraction of bodies.

The force of gravitational attraction

The basic calculation is as follows - the force of gravity is proportional to the multiplication of body mass by another, between which it is determined. This formula is also expressed as follows: the force is inversely proportional to the distance between objects squared.

The gravitational field is potential, which means that kinetic energy is conserved. This fact simplifies the solution of problems in which the force of attraction is measured.

Gravity in space

Despite the delusion of many, there is gravity in space. It is lower than on Earth, but still present.

As for the astronauts, who at first glance fly, they are actually in a state of slow fall. Visually, it seems that they are not attracted by anything, but in practice they experience gravity.

The strength of attraction depends on the distance, but no matter how large the distance between objects, they will continue to reach for each other. Mutual attraction will never be equal to zero.

Gravity in the solar system

In the solar system, not only the Earth has gravity. The planets, as well as the Sun, attract objects towards them.

Since the force is determined by the mass of the object, the Sun has the highest value. For example, if our planet has an indicator equal to one, then the indicator of a luminary will be almost twenty-eight.

The next, after the Sun, in gravity is Jupiter, so its force of attraction is three times higher than that of the Earth. Pluto has the smallest parameter.

For clarity, let's denote it like this, in theory, on the Sun, an average person would weigh about two tons, but on the smallest planet in our system - only four kilograms.

What determines the gravity of the planet

Gravitational pull, as already mentioned above, is the power with which the planet pulls objects located on its surface towards itself.

The force of attraction depends on the gravity of the object, the planet itself and the distance between them. If there are many kilometers, gravity is low, but it still keeps objects connected.

A few important and fascinating aspects related to gravity and its properties that are worth explaining to a child:

1. The phenomenon attracts everything, but never repels - this distinguishes it from other physical phenomena.
2. There is no zero indicator. It is impossible to simulate a situation in which pressure does not act, that is, gravity does not work.
3. The Earth is falling at an average speed of 11.2 kilometers per second, reaching this speed, you can leave the planet's attraction well.
4. The fact of the existence of gravitational waves has not been scientifically proven, this is just a guess. If ever they become visible, then many mysteries of the cosmos related to the interaction of bodies will be revealed to mankind.

According to the theory of basic relativity of a scientist like Einstein, gravity is a curvature of the basic parameters of the existence of the material world, which is the basis of the universe.

Gravity is the mutual attraction of two objects. The force of interaction depends on the gravity of the bodies and the distance between them. So far, not all the secrets of the phenomenon have been revealed, but today there are several dozen theories describing the concept and its properties.

The complexity of the studied objects affects the time of the study. In most cases, the dependence of mass and distance is simply taken.

We live on Earth, we move along its surface, as if along the edge of some rocky cliff that rises above a bottomless abyss. We are kept on this edge of the abyss only by what affects us. earth's gravity; we do not fall from the earth's surface just because we have, as they say, some certain weight. We would instantly fly off this “cliff” and rapidly fly into the abyss of space if the force of gravity of our planet suddenly ceased to act. We would endlessly rush about in the abyss of world space, knowing neither up nor down.

Earth locomotion

His movement on earth we, too, owe it to gravity. We walk the Earth and constantly overcome the resistance of this force, feeling its action, like some heavy load on our feet. This "load" especially makes itself felt when climbing a mountain, when you have to drag it, like some kind of heavy weights hanging from your feet. It no less sharply affects when descending the mountain, forcing us to speed up our steps. Overcoming the force of gravity when moving on the Earth. These directions - "up" and "down" - are indicated to us only by gravity. At all points on the earth's surface, it is directed almost to the center of the Earth. Therefore, the concepts of "bottom" and "top" will be diametrically opposed for the so-called antipodes, i.e. people living on diametrically opposite parts of the Earth's surface. For example, the direction that for those living in Moscow shows "down", for the inhabitants of Tierra del Fuego shows "up". Directions showing "down" for people at the pole and at the equator make a right angle; they are perpendicular to each other. Outside the Earth, when moving away from it, the force of gravity decreases, since the force of attraction decreases (the force of attraction of the Earth, like that of any other world body, extends indefinitely far in space) and the centrifugal force increases, which reduces the force of gravity. Therefore, the higher we lift some load, for example, in a balloon, the less this load will weigh.

Earth's centrifugal force

Due to diurnal rotation, centrifugal force of the earth. This force acts everywhere on the surface of the Earth in a direction perpendicular to the earth's axis and away from it. Centrifugal force small compared to gravity. At the equator, it reaches its greatest value. But even here, according to Newton's calculations, the centrifugal force is only 1/289 of the force of attraction. The farther north from the equator, the less centrifugal force. At the very pole it is zero.
The action of the centrifugal force of the Earth. At some height centrifugal force will increase so much that it will be equal to the force of attraction, and the force of gravity will first become equal to zero, and then, with increasing distance from the Earth, it will take a negative value and will continuously increase, being directed in the opposite direction with respect to the Earth.

Gravity

The resultant force of the Earth's attraction and the centrifugal force is called gravity. The force of gravity at all points on the earth's surface would be the same if our perfectly accurate and regular ball, if its mass were the same density everywhere, and, finally, if there were no daily rotation around the axis. But, since our Earth is not a regular ball, does not consist of rocks of the same density in all its parts and rotates all the time, then, therefore, gravity at each point on the earth's surface is slightly different. Therefore, at every point on the earth's surface the magnitude of the force of gravity depends on the magnitude of the centrifugal force, which reduces the force of attraction, on the density of the earth's rocks and the distance from the center of the earth. The greater this distance, the less gravity. The radii of the Earth, which at one end, as it were, rest against the earth's equator, are the largest. The radii that have the point of the North or South Pole as their end are the smallest. Therefore, all bodies at the equator have less gravity (less weight) than at the pole. It is known that gravity is greater at the pole than at the equator by 1/289. This difference in gravity of the same bodies at the equator and at the pole can be found by weighing them with a spring balance. If we weigh bodies on scales with weights, then we will not notice this difference. The balance will show the same weight both at the pole and at the equator; the weights, like the bodies that are being weighed, will also, of course, change in weight.
Spring scales as a way to measure gravity at the equator and at the pole. Let us assume that a ship with cargo weighs in the polar regions, near the pole, about 289 thousand tons. Upon arrival at ports near the equator, a ship with cargo will weigh only about 288,000 tons. Thus, at the equator, the ship lost about a thousand tons in weight. All bodies are kept on the earth's surface only due to the fact that gravity acts on them. In the morning, getting out of bed, you are able to lower your feet to the floor only because this force pulls them down.

Gravity inside the Earth

Let's see how it changes gravity inside the earth. As we go deeper into the Earth, the force of gravity continuously increases up to a certain depth. At a depth of about a thousand kilometers, gravity will have a maximum (greatest) value and will increase compared to its average value on the earth's surface (9.81 m / s) by approximately five percent. With further deepening, the force of gravity will continuously decrease and in the center of the Earth will be equal to zero.

Assumptions regarding the rotation of the Earth

Our earth revolving makes a complete revolution on its axis in 24 hours. The centrifugal force is known to increase in proportion to the square of the angular velocity. Therefore, if the Earth accelerates its rotation around its axis 17 times, then the centrifugal force will increase 17 times squared, i.e. 289 times. Under normal conditions, as mentioned above, the centrifugal force at the equator is 1/289 of the force of gravity. With an increase 17 times the force of attraction and the centrifugal force are made equal. The force of gravity - the resultant of these two forces - with such an increase in the speed of the axial rotation of the Earth will be equal to zero.
The value of centrifugal force during the rotation of the Earth. This speed of rotation of the Earth around its axis is called critical, since at such a speed of rotation of our planet all bodies at the equator would lose their weight. The duration of the day in this critical case will be approximately 1 hour and 25 minutes. With further acceleration of the Earth's rotation, all bodies (primarily at the equator) will first lose their weight, and then be thrown into space by the centrifugal force, and the Earth itself will be torn apart by the same force. Our conclusion would be correct if the Earth were an absolutely solid body and, when accelerating its rotational motion, would not change its shape, in other words, if the radius of the earth's equator retained its value. But it is known that with the acceleration of the Earth's rotation, its surface will have to undergo some deformation: it will begin to shrink in the direction of the poles and expand in the direction of the equator; it will take on a more and more flattened appearance. The length of the radius of the earth's equator will then begin to increase and thereby increase the centrifugal force. Thus, the bodies at the equator will lose their gravity before the Earth's rotation speed increases by 17 times, and the catastrophe with the Earth will come before the day will reduce its duration to 1 hour and 25 minutes. In other words, the critical speed of the Earth's rotation will be somewhat less, and the maximum length of the day will be somewhat longer. Imagine mentally that the speed of the Earth's rotation, due to some unknown reasons, will approach the critical one. What will become of the inhabitants of the earth then? First of all, everywhere on Earth a day will be, for example, about two or three hours. Day and night will change kaleidoscopically quickly. The sun, as in a planetarium, will move very quickly across the sky, and as soon as you wake up and wash yourself, it will already hide behind the horizon, and night will come to replace it. People will no longer accurately navigate in time. No one will know what day of the month it is and what day of the week it is. Normal human life will be disorganized. Pendulum clocks will slow down and then stop everywhere. They walk because gravity acts on them. After all, in our everyday life, when “walkers” begin to lag behind or rush, it is necessary to shorten or lengthen their pendulum, or even hang some additional weight on the pendulum. Bodies at the equator will lose their weight. Under these imaginary conditions it will be easy to lift very heavy bodies. It will not be difficult to shoulder a horse, an elephant, or even lift a whole house. The birds will lose their ability to land. Here is a flock of sparrows circling over a trough with water. They chirp loudly, but are unable to descend. A handful of grain thrown by him would hang over the Earth in separate grains. Let, further, the speed of rotation of the Earth more and more approaches the critical one. Our planet is strongly deformed and takes on an increasingly flattened appearance. It is likened to a rapidly rotating carousel and threatens to throw off its inhabitants. The rivers will then stop flowing. They will be long stagnant swamps. Huge ocean ships will barely touch the water surface with their bottoms, submarines will not be able to dive into the depths of the sea, fish and marine animals will swim on the surface of the seas and oceans, they will no longer be able to hide in the depths of the sea. Sailors will no longer be able to anchor, they will no longer own the rudders of their ships, large and small ships will stand motionless. Here is another imaginary picture. Passenger railway train stands at the station. The whistle has already been blown; the train must leave. The driver took all necessary measures. The stoker generously throws coal into the furnace. Large sparks fly from the chimney of a steam locomotive. The wheels are turning desperately. But the locomotive is standing still. Its wheels do not touch the rails and there is no friction between them. The moment will come when people will not be able to go down to the floor; they will stick like flies to the ceiling. Let the speed of rotation of the Earth keep increasing. The centrifugal force is more and more superior in its magnitude to the force of attraction... Then people, animals, household items, houses, all objects on the Earth, its entire animal world will be thrown into the world space. The Australian continent will separate from the Earth and hang in space like a colossal black cloud. Africa will fly into the depths of the silent abyss, away from the Earth. The waters of the Indian Ocean will turn into a huge number of spherical drops and will also fly into boundless distances. The Mediterranean Sea, not having yet had time to turn into giant accumulations of drops, will separate from the bottom with its entire thickness of water, along which it will be possible to freely pass from Naples to Algiers. Finally, the speed of rotation will increase so much, the centrifugal force will increase so much that the whole Earth will be torn apart. However, this cannot happen either. The speed of the Earth's rotation, as we said above, does not increase, but on the contrary, it even decreases a little - however, it is so small that, as we already know, in 50 thousand years the duration of the day increases by only one second. In other words, the Earth now rotates at such a speed that is necessary for the flora and fauna of our planet to flourish under the calorific, life-giving rays of the Sun for many millennia.

Friction value

Let's see now what friction matters and what would happen if it were not there. Friction, as we know, has a harmful effect on our clothes: coats wear out the sleeves first, and boots the soles, since the sleeves and soles are most subject to friction. But imagine for a moment that the surface of our planet was, as it were, well polished, perfectly smooth, and the possibility of friction would be excluded. Could we walk on such a surface? Of course not. Everyone knows that even on ice and on a rubbed floor it is very difficult to walk and you have to be careful not to fall. But the surface of the ice and the rubbed floor still has some friction.
Friction force on ice. If the friction force disappeared on the surface of the Earth, then indescribable chaos would forever reign on our planet. If there is no friction, the sea will rage forever and the storm will never subside. Sand tornadoes will not stop hanging over the Earth, and the wind will constantly blow. The melodic sounds of the piano, violin and the terrible roar of predatory animals will mix and spread endlessly in the air. In the absence of friction, a body in motion would never stop. On an absolutely smooth earth's surface, various bodies and objects would forever be mixed in a wide variety of directions. Ridiculous and tragic would be the world of the Earth, if there were no friction and attraction of the Earth.