Gravity - what is it? The power of gravity. Earth's Gravity

Mankind has long thought about how the surrounding world works. Why grass grows, why does the sun shine, why can not we fly ... The latter, by the way, has always been especially interested in people. Now we know that the reason for everything is gravity. What it is, and why this phenomenon is so important in the scale of the universe, we will consider today.

Introduction

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

Over the centuries, scientists have observed the attraction, trying to understand and measure it. Finally, in the last few decades, even a phenomenon such 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 modern science?

Scientific definition

If you study the works of ancient thinkers, you can find out that the Latin word "gravitas" means "heaviness", "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 slower than the speed of light, then Newton's theory applies to them. If the situation is reversed, then Einstein's conclusions should be used.

Immediately make a reservation: at the present time the very nature of gravity is not fully understood in principle. We still do not fully know what it is.

The theories of Newton and Einstein

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

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

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

\ [F = γ \ frac [-1.2] {m_1 m_2} {r ^ 2} \]

By γ is meant the gravitational constant (sometimes the symbol G is used), whose value is equal to 6.67545 × 10-11 m³ / (kg · s²).

Interaction between elementary particles

The incredible complexity of the surrounding space is largely related to an infinite number of elementary particles. Between them there are also different interactions at those levels, of which we can only guess. However, all types of interaction of elementary particles differ significantly in their strength.

The most powerful of all known forces connect 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 core only by ordinary electromagnetic interaction. To stop it, sometimes enough energy that appears as a result of the most common chemical reaction. Gravitation (what it is, you already know) in the version 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. Strangely enough, but behind the movement of heavenly bodies, whose mass sometimes can not imagine, they are "watching". All this is possible due to two features of gravity, which are especially pronounced in the case of large physical bodies:

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

The formation of a more or less harmonious theory of gravity has occurred relatively recently, and precisely from the results of centuries of 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 that time, with their valuable observations helped to prepare the ground for new discoveries.

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 gravitation, 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. It should be understood that the term "zero gravity", which is often found in the circumpolar circles, is extremely incorrect: even weightlessness in space does not mean that the attraction of a massive object does not work on a person or a spacecraft.

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 through this action.

Thus, the forces of gravity are proportional to the mass of objects. In a numerical sense, they can be expressed by obtaining the product of the masses of both bodies under consideration. This force is strictly subject to inverse dependence on the square of the distance between objects. All other interactions completely depend on the distances between the two bodies.

Mass as the cornerstone of theory

The mass of objects became a special controversial point, around which the whole modern theory of gravitation and relativity of Einstein is built. If you remember Newton's Second Law, you probably know that mass is an indispensable characteristic of any physical material body. It shows how the object will behave if the force is applied to it, regardless of its origin.

Since all bodies (according to Newton) are accelerated by the action of external forces, it is the mass that determines how large this acceleration will be. Let's consider a more understandable example. Imagine a scooter and a bus: if you apply absolutely the same force to them, they will reach different speeds for the same time. All this explains 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 completely opposite role to that which it plays with respect to the force and acceleration of the object. It is the primary source of the attraction itself. If you take two bodies and see with what power they attract the 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 you consider Newton's Third Law, you can make sure 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 are talking about the force with which the body is attracted to the surface of the planet, as its weight.

Let's sum up some results. So, the mass is closely related to force and acceleration. At the same time it is she who determines the force with which attraction 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. Suppose we have two bodies. We assign one of them a mass z, and the other - Z. Both objects are dropped to the ground, where they fall freely.

How is the ratio of the forces of attraction determined? It shows the simplest mathematical formula - z / Z. That's just the acceleration, obtained by them as a result of the action of the force of attraction, will be absolutely identical. Simply put, the acceleration that the body has in the gravitational field does not depend on its properties.

What determines the acceleration in this case?

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

The importance of G

From the school course of physics, we remember that the acceleration of gravity on the surface of our planet (Earth's gravity) is 10 m / sec.² (9.8 of course, but this value is used for simplicity of calculations). Thus, if we do not take into account the air resistance (at a significant height with a small drop distance), then the effect will be obtained when the body acquires an acceleration increment of 10 m / sec. Every second. So, the book that fell from the second floor of the house, by the end of its flight will move at a speed of 30-40 m / sec. Simply put, 10 m / s is the "speed" of gravity within the Earth.

Acceleration of free fall in the physical literature is denoted by the letter "g". Since the shape of the Earth to some extent more like a mandarin than a ball, the value of this magnitude is far from the same in all its regions. Thus, the acceleration is higher at the poles, and at the tops of high mountains it becomes smaller.

Even in the extractive industry, gravity plays the least role. The physics of this phenomenon can sometimes save a lot of time. So, geologists are especially interested in an ideally precise definition of g, since this allows for the exploration and discovery of mineral deposits with exceptional accuracy. By the way, what does the gravity formula look like in which the quantity considered by us plays an important role? Here she is:

F = G × M1 × M2 / R2

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

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

The theory of relativity, the work of Albert Einstein

In the days of Isaac Newton, it was believed that the reference points can be represented in the form of some rigid "rods", by 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 will be in the same time space. In those years, this provision was considered so obvious that no attempts were made to challenge it 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 moves much slower than the speed of light. Simply put, if one observer moving slower than the speed of light will follow two events, then they will occur for him at a time. Accordingly, for the second observer? The speed of which is the same or greater, events can occur at different times.

But how is the force of gravity connected with the theory of relativity? We will expand this question in detail.

The connection between the theory of relativity and gravitational forces

In recent years, a huge amount of discoveries have been made in the field of subatomic particles. The belief that we are about to find the final particle, beyond which our world can not crumble, will grow stronger. The more insistent is the need to find out exactly how the fundamental forces that were discovered in the last century, and even earlier, influence the smallest "bricks" of our universe. It is especially insulting that the very nature of gravity has not yet been explained.

This is why, after Einstein, who established the "incapacity" of Newton's classical mechanics in the field under consideration, the researchers focused on a complete rethinking of the data obtained earlier. In many respects, the gravity itself underwent a revision. What is this at the level of subatomic particles? 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 can be explained quite simply by drawing analogies from the field of electrodynamics. One could assume that the gravitational field spreads like a magnetic field, after which it can be declared a "mediator" in the interactions of celestial bodies, explaining many inconsistencies between the old and new theories. The point is that then the relative propagation velocities of the forces under consideration turned out to be much lower than the light velocity. So how do gravity and time relate?

In principle, Einstein himself almost succeeded in constructing a relativistic theory on the basis of precisely such views, but only one circumstance prevented his intention. None of the scientists of that time had at all any information 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 the universally recognized source of the emergence of powerful gravitational fields.

Large speeds strongly affect the masses of bodies, and this is not at all similar to the interaction of speed and charge. The higher the speed, the greater the mass of the body. The problem is that the latter value would automatically become infinite in the case of motion at the speed of light or higher. And so Einstein concluded that there is not a gravitational field, 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 for a time it can not affect. However, the genius physics of modernity of Stephen Hawking has another point of view. But that's another story ...