Gravity is not at all the “Law of Universal Gravitation.” What is gravity

Since ancient times, humanity 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 gravity is the reason for everything. What it is, and why this phenomenon is so important on the scale of the Universe, we will consider today.

Introductory part

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 theory of gravity was formulated by a genius whose hypotheses predetermined the development of physics for many centuries to come. Albert Einstein, one of the greatest minds of the last century, developed and continued (albeit in a completely different direction) this teaching.

For centuries, scientists have observed gravity and tried to understand and measure it. Finally, in the last few decades, even such a phenomenon as gravity has been put at the service of humanity (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 call this 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 situation is the other way around, Einstein's conclusions should be used.

Let’s make a reservation right away: at present, the very nature of gravity is not fully understood in principle. We still don’t fully understand what it is.

Theories of Newton and Einstein

According to the classical teaching of Isaac Newton, all bodies attract each other with a force directly proportional to their mass, inversely proportional to the square of the distance that lies between them. Einstein 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, Einstein’s classical equation does not even provide for the chance that space will continue to influence matter and the resulting magnetic field.

The law of gravity (universal gravitation) is best known, the mathematical expression of which belongs to Newton:

\[ F = γ \frac[-1.2](m_1 m_2)(r^2) \]

γ refers to 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 between elementary particles differ significantly in their strength.

The most powerful 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 “attached” 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 (you already know what it is) in the form of atoms and subatomic particles is the easiest type of interaction.

The gravitational field in this case is so weak that it is difficult to imagine. Oddly enough, it is they who “monitor” the movement of celestial bodies, whose mass is sometimes impossible to imagine. All this is possible thanks 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. Thus, the Earth’s gravity holds even the Moon in its field, and a similar force from Jupiter easily supports the orbits of several satellites at once, the mass of each of which is quite comparable to that of the Earth!
• In addition, it always provides attraction between objects, and with distance this force weakens at a small speed.

The formation of a more or less coherent theory of gravity occurred relatively recently, and precisely based on the results of centuries-old observations of the movement 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 probable interactions. Galileo and Kepler, two outstanding astronomers of that time, helped prepare the ground 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 mathematically. 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 spaceship is not affected by the gravity of some massive object.

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

Thus, gravitational forces are proportional to the mass of objects. They can be expressed numerically by obtaining the product of the masses of both bodies under consideration. This force strictly obeys the inverse relationship to the square of the distance between objects. All other interactions depend completely differently on the distances between two bodies.

Mass as the cornerstone of the theory

The mass of objects has become a special point of contention around which Einstein's entire modern theory of gravity and relativity is built. If you remember the Second, 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 exposed to an external force, it is the mass that determines how large this acceleration will be. Let's look at a more understandable example. Imagine a scooter and a bus: if you apply exactly the same force to them, they will reach different speeds in different times. The theory of gravity explains all this.

What is the relationship between mass and gravity?

If we talk about gravity, then mass in this phenomenon plays a role completely opposite to the one 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 look at the force with which 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 gravity is directly proportional to the mass of the body.

If we consider Newton's Third Law, we can see that it says exactly the same thing. The force of gravity, which acts on two bodies located at equal distances 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 summarize 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 that in the same gravitational field the acceleration of completely different objects will be equal. Let's assume that we have two bodies. Let's assign mass z to one of them, and mass Z to the other. Both objects are dropped to the ground, where they fall freely.

How is the ratio of attractive forces determined? It is shown by the simplest mathematical formula - z/Z. But the acceleration they receive as a result of the force of gravity will be absolutely 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 equal acceleration of different bodies in a gravitational field has been discovered for a relatively long time. These phenomena received the following name: “The principle of equivalence.” This term once again emphasizes that acceleration and inertia are often equivalent (to a certain extent, of course).

About the importance of the G value

From the school physics course, we remember that the acceleration of gravity on the surface of our planet (Earth’s gravity) is equal to 10 m/sec.² (9.8, of course, but this value is used for simplicity of calculations). Thus, if you do not take into account air resistance (at a significant height with a short fall distance), you will get the effect when the body acquires an acceleration increment of 10 m/sec. every second. So, a book that fell 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.

The acceleration of gravity in the physical literature is denoted by the letter “g”. Since the shape of the Earth is to a certain extent more reminiscent of a tangerine than a sphere, the value of this quantity is not the same in all its regions. So, the acceleration is higher at the poles, and at the tops of high mountains it becomes less.

Even in the mining industry, gravity plays an important role. The physics of this phenomenon can sometimes save a lot of time. Thus, geologists are especially interested in the perfectly accurate determination of g, since this allows them to explore and locate mineral deposits with exceptional accuracy. By the way, what does the gravitation formula look like, in which the quantity we considered plays an important role? Here she is:

Note! In this case, the gravitation formula means by G the “gravitational constant”, the meaning 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 humanity owes the modern understanding of the very nature of the space-time continuum.

Theory of relativity, works of Albert Einstein

In the time of Isaac Newton, it was believed that reference points can be represented in the form of some kind of rigid “rods”, with the help of which the position of a body in a spatial coordinate system is established. At the same time, it was assumed that all observers who mark these coordinates will be in the same 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 the boundaries of our planet there are no deviations in this rule.

Einstein proved that the accuracy of the measurement would really matter if a hypothetical clock moved significantly 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? whose speed is the same or greater, events can occur at different times.

But how does gravity relate to the theory of relativity? Let's look at this question in detail.

The connection between the theory of relativity and gravitational forces

In recent years, a huge number of discoveries have been made in the field of subatomic particles. The conviction is growing stronger that we are about to find the final particle, beyond which our world cannot fragment. The more insistent becomes the need to find out exactly how the smallest “building blocks” of our universe are influenced 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 “incompetence” of Newton’s classical mechanics in the area under consideration, researchers focused on a complete rethinking of the previously obtained data. Gravity itself has undergone a major revision. What is it at the subatomic particle level? Does it have any significance in this amazing multidimensional world?

A simple solution?

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

In principle, Einstein himself almost succeeded in constructing a relativistic theory based on precisely such views, but 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 is known, they were precisely the generally accepted source of the emergence of powerful gravitational fields.

High speeds greatly affect the masses of bodies, and this is in no way similar to the interaction of speed and charge. The higher the speed, the greater the body mass. The problem is that the latter value would automatically become infinite if moving at the speed of light or faster. Therefore, Einstein concluded that there is not a gravitational field, but a tensor field, to describe 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 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...

Gravity is a seemingly simple concept, known to every person since school. We all remember the story of how an apple fell on Newton's head and he discovered the law of universal gravitation. However, everything is not as simple as it seems. In that article we will try to give a clear and comprehensive answer to the question: what is gravity? We will also consider the main myths and misconceptions about this interesting phenomenon.

In simple terms, gravity is the attraction between any two objects in the universe. Gravity can be determined by knowing the mass of bodies and the distance from one to another. The stronger the gravitational field, the greater the weight of the body and the higher its acceleration. For example, on the Moon the weight of an astronaut will be six times less than on Earth. The strength of the gravitational field depends on the size of the object it surrounds. Thus, the lunar gravity is six times lower than the earth’s. This was first scientifically substantiated and proven using mathematical calculations back in the 17th century by Isaac Newton.

What fell on Newton's head?

Despite the fact that the great English scientist himself partially confirmed the well-known legend about the apple and the head injury, nevertheless, now we can say with confidence that during the discovery of the law of universal gravitation there were no injuries or insights. The foundation that laid the foundation for a new era in the natural sciences was the work “Mathematical Principles of Natural Philosophy.” In it, Newton describes the law of gravity and important laws of mechanics that he discovered over many years of hard work. The famous physicist was a leisurely and judicious person, as befits a brilliant scientist. And therefore, more than 20 years passed from the beginning of thinking about the nature of gravity to the publication of a scientific work about it. However, the legend about the fallen fruit could have some real basis, but the physicist’s head definitely remained intact.

The laws of attraction were studied before Isaac Newton by a variety of scientific figures. But only he was the first to mathematically prove the direct relationship between gravity and the movement of planets. That is, an apple falling from a branch and the rotation of the moon around the earth are controlled by the same force - gravity. And it acts on any two bodies in the universe. These discoveries laid the foundation for the so-called celestial mechanics, as well as the science of dynamics. The Newtonian model dominated science for more than two centuries until the advent of the theory of relativity and quantum mechanics.

What do modern scientists think about gravity?

Gravity is the weakest of the four currently known fundamental interactions to which all particles and bodies composed of them are subject. In addition to gravitational interaction, this also includes electromagnetic, strong and weak. They are studied on the basis of different theories, for example, in the approximate speeds of small gravity, Newton’s theory of gravity is used. In the general case, Einstein's general theory of relativity is used. In addition, the description of gravity in the quantum limit will have to be carried out using a quantum theory that has not yet appeared.

Of course, today physics is complex and goes far beyond the ordinary person’s understanding of the world around him. But it is necessary to be interested in it at least at the level of basic concepts, because it is quite possible that in the near future we may witness amazing discoveries in this area that will radically change the life of mankind. It will be awkward if you don't understand what's going on at all.

Myths about gravity

Not only ignorance, but also constant new discoveries in this scientific field give rise to various absurdities and myths about gravity. So, a few common misconceptions about this unique phenomenon:

• Artificial satellites will never leave the Earth's orbit and will forever revolve around it. It is not true. The fact is that in addition to gravity in space, there are various other factors that influence the orbit of bodies. This includes the braking of the atmosphere for low orbits and the gravitational fields of the Moon and other planets. Most likely, if a satellite is allowed to spin uncontrolled for a long time, its orbit will change, and eventually it will either fly off into space or fall onto the surface of a nearby body.
• There is no gravity in space. Even at stations where astronauts are in weightlessness there is quite strong gravity, slightly less than on Earth. Why then don't they fall? We can say that the station employees seem to be in a state of constant falling, but they will not fall.
• An object approaching a black hole will be torn apart. Quite a well-known myth. The gravitational force of a black hole will indeed increase as you approach it, but it is not at all necessary that the tidal forces will be so powerful. Most likely they have a finite value at the event horizon, since the distance is calculated from the center of the hole.