Earth gravity. Earth's gravitational field

Once the famous French physicist and astronomer Arago said that if a person did not constantly observe the fall of bodies, then the force of gravity of the earth would be the most amazing phenomenon for him. We often do not notice many things just because we have long been accustomed to them. And if we are told that the force of gravitational attraction acts between any two bodies, it is rather difficult to believe, since we simply do not see this in everyday life. Why is this happening?

Omnipresent and invisible forces of gravity

Why are people, cars, stones not attracted to each other? The reason is that the force of attraction between small objects is very small. The easiest way to show this is with an illustrative example. Suppose that two people are standing opposite each other at a distance of two meters. If we assume that both of them have an average weight, then the force of attraction between them will be less than one hundredth of a milligram. Not every device could register such an impact. In fact, it is equal to the force with which a weight of 1/100,000 grams exerts pressure on the scales. Therefore, it is clear that such an impact is simply not able to move people from their place, because the friction force of their soles against the earth's surface, equal to about 30% of the body weight, interferes. In order to move a person standing on a wooden floor, you will need to apply a force of at least 20 kg. If we compare this value with one hundredth of a milligram, it becomes obvious that the force of attraction between different objects in real life is negligible.

If there were no friction...

Let's fantasize a little. Imagine that the force of friction suddenly ceased to exist. What would then happen in the above example? The force of attraction would be able to freely manifest itself in action, but because of its small magnitude, the convergence of two people would be very, very slow. So, during the first 60 minutes, they would approach each other by only 3 cm, after an hour - by another 9 cm, and after three hours - by as much as 15 cm. But, despite the acceleration, in order for both people to come close, it will take at least five hours.

Let's go to space

The force of attraction, scanty in relation to small bodies, reaches impressive values, if we talk about celestial bodies that have a colossal mass. So, even a planet as far away from us as Neptune, which is located almost at the very edge of our solar system, has an impact on Earth of as much as 18,000,000 tons! The Sun is 150 million km away. This distance seems huge, but if it were not for the force of gravity, which firmly holds our planet in orbit, the Earth would have rushed off to surf the bottomless depths of world space long ago.

Why don't celestial bodies collide?

If the effect of gravity in space is so strong, what then prevents the collision of stars? This question was asked by Newton. In principle, if the celestial bodies were in a stationary state, then sooner or later they would merge into one heap. But since planets, stars and galaxies move, this does not happen. They seem to "fall" on the centers of mass that attract them and constantly "miss", while describing their circular or elongated orbits. At the same time, the gravity that exists between them is so small that it practically does not interfere with their movement.

Gravity, also known as attraction or gravitation, is a universal property of matter that all objects and bodies in the Universe possess. The essence of gravity is that all material bodies attract to themselves all other bodies that are around.

Earth gravity

If gravity is a general concept and quality that all objects in the Universe possess, then the earth's attraction is a special case of this all-encompassing phenomenon. The earth attracts to itself all the material objects that are on it. Thanks to this, people and animals can safely move around the earth, rivers, seas and oceans can remain within their shores, and air can not fly through the vast expanses of the Cosmos, but form the atmosphere of our planet.

A fair question arises: if all objects have gravity, why does the Earth attract people and animals to itself, and not vice versa? Firstly, we also attract the Earth to ourselves, it's just that compared to its force of attraction, our gravity is negligible. Secondly, the force of gravity is directly proportional to the mass of the body: the smaller the mass of the body, the lower its gravitational forces.

The second indicator on which the force of attraction depends is the distance between objects: the greater the distance, the less the effect of gravity. Including due to this, the planets move in their orbits, and do not fall on each other.

It is noteworthy that the Earth, the Moon, the Sun and other planets owe their spherical shape precisely to the force of gravity. It acts in the direction of the center, pulling towards it the substance that makes up the "body" of the planet.

Earth's gravitational field

The gravitational field of the Earth is a force energy field that is formed around our planet due to the action of two forces:

• gravity;
• centrifugal force, which owes its appearance to the rotation of the Earth around its axis (daily rotation).

Since both gravity and centrifugal force act constantly, the gravitational field is also a constant phenomenon.

The gravitational forces of the Sun, the Moon and some other celestial bodies, as well as the atmospheric masses of the Earth, have an insignificant effect on the field.

Law of gravity and Sir Isaac Newton

The English physicist, Sir Isaac Newton, according to a well-known legend, once walking in the garden during the day, saw the moon in the sky. At the same time, an apple fell from the branch. Newton was then studying the law of motion and knew that an apple falls under the influence of a gravitational field, and the Moon revolves in an orbit around the Earth.

And then the idea came to the mind of a brilliant scientist, illuminated by insight, that perhaps the apple falls to the earth, obeying the same force due to which the Moon is in its orbit, and does not rush randomly throughout the galaxy. This is how the law of universal gravitation, also known as Newton's Third Law, was discovered.

In the language of mathematical formulas, this law looks like this:

F=GMm/D2 ,

Where F- force of mutual gravitation between two bodies;

M- mass of the first body;

m- mass of the second body;

D2- distance between two bodies;

G- gravitational constant, equal to 6.67x10 -11.

gravity, or gravity, is a property that all bodies and objects possess, because gravity is an inherent property of matter (). The essence of the phenomenon of gravity is that all bodies attract other bodies to themselves. For example, the Earth attracts everything that is on it and that is why any object that has no support falls to the Earth. It is thanks to the force of gravity that we can walk on the Earth, and do not fly away into space. If there were no gravity, then all the water would splash out of the oceans, and the air would fly into outer space.

The Earth also attracts the Moon, which otherwise would have flown away long ago.

Why then does the moon not fall to the earth? And she would have fallen if she had stood still! The moon does not fall to the Earth because it is constantly moving - revolving around the Earth.

Why do we not notice the force of gravity in everyday life, if all bodies attract each other? The point is that gravity is a very weak force. It depends on two factors: the mass of objects and the distance between them. The smaller the mass of an object, the weaker its gravitational force. Therefore, for bodies with a small mass, it is simply invisible. Even the attraction of such a large object as Mount Everest is only 0.001% of the earth's gravity. The mutual attraction of two people of average weight with a distance of 1 meter between them does not exceed 0.03 milligrams.

When it comes to planets and stars, their gravitational force is already very high, because they are millions and billions of times larger than ourselves and what surrounds us. That is why the button that comes off the coat is not attracted to the person, but falls to the ground, although he is closer to the button than the earth - after all, the mass of the Earth is incomparably greater than the mass of a person.

The dependence of gravity on distance is manifested in the fact that the farther objects are from each other, the weaker they are attracted to each other.

The law of universal gravitation was discovered by Isaac Newton, an English physicist, mathematician and astronomer. He was the first to guess, and then proved that the reason that causes the fall of a stone to the Earth, the movement of the Moon around the Earth and the planets around the Sun is the same - it is the gravitational force acting between any bodies of the Universe.

Newton said that he was prompted to discover the law of universal gravitation by observing an apple that fell from a branch while he was walking in the garden. And at this very time he was working on the laws of motion, and already knew that the apple fell under the influence of the Earth's gravity. He also knew that the Moon does not just hang in the sky, but rotates in orbit around the Earth, which means that some kind of force acts on it, which keeps it from falling out of orbit and flying into outer space. Then it occurred to him that perhaps it is the same force that makes both the apple fall to the earth and the moon to remain in orbit around the earth.

The significance of this discovery for mankind is enormous. With the help of this law, astronomers determine with great accuracy the position of celestial bodies in the sky for many decades to come and calculate their trajectories. The law of universal gravitation is used in calculations of the motion of artificial Earth satellites and interplanetary automatic vehicles. Using the law of universal gravitation, you can calculate the mass of the planets and their satellites. The law of universal gravitation explains phenomena such as ebbs and flows.

But the most striking example of the role of this law for science is the history of the discovery of the planet Neptune. In 1781, the English astronomer William Herschel discovered the planet Uranus. Its orbit was calculated and a table of the positions of this planet was compiled for many years to come. However, checking this table showed that Uranus does not move exactly as it was calculated. Scientists have suggested that the deviation in the motion of Uranus is caused by the attraction of an unknown planet, located even further from the Sun than Uranus. Knowing the deviations from the calculated trajectory, the Englishman Adams and the Frenchman Leverrier, using the law of universal gravitation, calculated the position of this planet in the sky. Adams completed the calculations earlier, but the observers to whom he reported his results were in no hurry to verify. In the meantime, Leverrier, having finished his calculations, indicated to the German astronomer Halle the place where to look for an unknown planet. On the very first evening, September 28, 1846, Halle, pointing the telescope at the indicated place, discovered a new planet! They named her Neptune. It was the first planet that was discovered not in the course of observations of the sky, but as a result of mathematical calculations (as they say, "on the tip of a pen"). In the same way, Pluto was discovered in 1930.

The Earth attracts, the Sun, the Moon, planets, stars - giant celestial bodies attract. Do small objects around us attract? Here are two trucks standing side by side on the street - is there an attraction between them? There are cabinets, tables, chairs in your room - do they attract each other? Do even smaller objects attract - books, dishes placed on the table? Finally, do we ourselves attract?

Yes, all these things attract although we usually don't notice it. The law of gravity is the universal law of nature. Why is the attraction of small bodies imperceptible? First of all, because it is very small. After all, the force of attraction depends on the mass of the bodies. Mass of the Earth huge - thousands of billions of billions of tons. How insignificant in comparison with this is the mass, and hence the force of attraction of the objects around us! Distance is also important. For the effect of attraction of small objects to be noticeable, the distance between our cabinets or plates is too large for this.

Here are some examples of gravity in the world of small bodies. Even two ships with a mass of 25,000 tons, standing in the roadstead at a distance of 100 m from one another, attract each other with a force of 400 g. Between two 50-ton wagons at the same distance, the force of attraction is 0.0016 g. For objects of smaller mass, attraction at a smaller distance must be considered. Between two heavy metal balls of 1 ton at a distance of 1 m between their centers, the force of attraction is 6 2/3 thousandths of a gram. And two people of average weight at the same distance of 1 m attract each other with a force of only a hundred-thousandths of a gram. Such "strength" will not break even a thin web. But two apples of 100 g each attract each other, however, even at a distance of 10 cm, the force of attraction between them is only one 250 millionth of a gram.

No matter how small these forces of attraction between the small objects around us, they still should somehow manifest themselves. Like all forces, they, it would seem, could set objects in motion and cause them to approach each other - albeit very slowly. Our furniture and other items in the room would have to slowly move closer and huddle somewhere in one place. The dishes placed on the table should also get closer ...

Why doesn't this happen? Turns out it prevents friction. Between the legs of the furniture and the floor, between the dishes and the tablecloth, friction forces act that slow down the movement. In this case, the friction force is much greater than the force of attraction between small objects. We have seen that two people at a distance of 1 m attract each other with a force of a hundred-thousandths of a gram. And to overcome the friction between the soles of their feet and the floor, you need a force of at least 20 kg, that is, about a billion times greater!

Now, if there were no friction, if for some reason it disappeared, the picture would become completely different. We would not be able to walk, as the niches of the legs would slide along the floor and could not push off from it. Transport would also stop. Nails would fall out, screws would come out, fabrics would fall apart, clothes would fall off our shoulders, and clothes would flare, since everything is held together by friction.

In this imaginary world without friction, attraction between small objects would be noticeable. It would cause them to approach each other. We would be surprised to see how our beds, tables and chairs would begin to slowly slide towards each other and eventually huddle in a common pile.

True, the objects would crawl towards each other very slowly, since their negligible force of attraction would set them in motion. However, the speed would gradually increase. So, two people standing at a distance of 2 m from each other, during the first hour would approach only 3 cm. But during the second hour - already by 9 cm, and during the third, by 15 cm. And only after five hours they would come into close contact with each other. The speed of rapprochement would increase with every second and with a constant force. But in this case, as the distance decreases, the force of attraction would increase. And from this, the rapprochement would be faster.

Note that the force of friction between objects and their support depends on their weight - that is, on the force of gravity of the earth.

It turns out that the proximity of the Earth and its huge attraction cause that great friction, which interferes with the action of attraction between small bodies. And so away from Earth and other large cosmic bodies - somewhere in interstellar space - the attraction between small objects (at short distances) would manifest itself more noticeably and cause them to slowly move towards each other