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 power 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.

That's when we are talking about the planets and stars, their gravitational force is already very strong, because they are millions and billions of times larger than ourselves and what surrounds us. That is why a button that has come off a coat is not attracted to a 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 space. 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 the position with great accuracy. celestial bodies in the sky for many decades to come and their trajectories are calculated. 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 story 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 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.

Children are sometimes very curious and sometimes ask questions that are very difficult to answer. For example, why don't people fall off the surface of the Earth? After all, it is round, rotates around its axis, and even moves in the vast expanses of the Universe among a huge number of stars. Why, at the same time, can a person walk calmly, sit on the couch and not worry at all? In addition, some peoples live “upside down”. Yes, and a sandwich that is dropped falls to the ground, and does not fly into the sky. Maybe something pulls us to the Earth and we can not come off?

Why don't people fall off the surface of the earth?

If the child began to ask such questions, then you can tell him about gravity, or in another way - about the earth's attraction. After all, it is this phenomenon that causes any object to strive towards the surface of the Earth. Thanks to gravity, a person does not fall and does not fly away.

Earth gravity allows the population of the planet to move freely on its surface, erect buildings and all kinds of structures, sled or ski down the mountain. Thanks to gravity, objects fall down instead of flying up. To test this in practice, it is enough to toss the ball. He will fall to the ground anyway. That's why people don't fall off the surface of the earth.

But what about the Moon?

Of course, gravity does not allow a person to fall from the Earth. But another question arises - why does the Moon not fall on it? The answer is very simple. The moon moves constantly in the orbit of our planet. If it stops, it will surely fall to the surface of the planet. This can also be verified by doing a little experiment. To do this, tie a string to the nut and unwind it. It will move in the air until it stops. If you stop spinning, then the nut will simply fall. It is also worth noting that the moon's gravity is about 6 times weaker than the earth's gravity. It is for this reason that weightlessness is felt here.

everyone has

Almost all objects have the power of attraction: animals, cars, buildings, people and even furniture. And a person is not attracted to another person just because our gravity is low enough.

The force of attraction directly depends on the distance between the individual bodies, as well as on their mass. Since a person weighs very little, he is attracted not to other objects, but to the Earth. After all, its mass is much larger. The earth is very big. The mass of our planet is enormous. Naturally, the force of attraction is great. Because of this, all objects are attracted to the Earth.

When was gravity discovered?

Children are not interested in boring facts. But the story of the discovery of gravity is quite strange and funny. was discovered by Isaac Newton. The scientist sat under an apple tree and thought about the universe. At that moment, a fruit fell on his head. As a result of this, the scientist realized that all objects fall exactly down, because there is an attractive force. continued his research. The scientist found that the force of gravity depends on the mass of bodies, as well as on the distance between them. He also proved that on long distance objects cannot influence each other. This is how the law of gravity came about.

Does everything fall down: a small experiment

In order for a child to better understand why people do not fall from the surface of the Earth, you can conduct a small experiment. This will require:

1. Cardboard.
2. Cup.
3. Water.

The glass must be filled with liquid to the very brim. After that, the container should be covered with cardboard so that air does not get inside. After that, you need to turn the glass upside down, while holding the cardboard with your hand. It is best to experiment on the sink.

What happened? Cardboard and water remained in place. The fact is that there is absolutely no air inside the container. Cardboard and water are unable to overcome the air pressure from outside. It is for this reason that they remain in their places.

Mankind has been striving for space for a long time. But how to get off the ground? What prevented man from flying up to the stars?

As we already know, this was prevented by terrestrial gravity, or the gravitational force of the Earth - the main obstacle to space flights.

Gravity

All physical bodies located on Earth, subject to the action law of gravity . According to this law, they all attract each other, that is, they act on each other with a force called gravitational force or gravity .

The magnitude of this force is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between them.

Since the mass of the Earth is very large and significantly exceeds the mass of any material body located on its surface, the gravitational force of the Earth is much greater than the gravitational forces of all other bodies. We can say that in comparison with the gravitational force of the Earth, they are generally invisible.

The earth attracts absolutely everything. Whatever object we throw up, under the influence of gravity, it will definitely return to Earth. Drops of rain fall down, water flows down from the mountains, leaves fall from the trees. Any item we drop also falls on the floor instead of the ceiling.

The main obstacle to space travel

Earth's gravity does not allow aircraft leave the earth. And it is not easy to overcome it. But man has learned to do it.

Let's observe the ball lying on the table. If he rolls off the table, the Earth's gravity will cause him to fall to the floor. But if we take the ball and throw it with force into the distance, then it will not fall immediately, but after some time, describing the trajectory in the air. Why was he able to overcome the earth's gravity even for a short time?

And here's what happened. We applied a force to it, thereby imparting acceleration, and the ball began to move. And the more acceleration the ball receives, the higher its speed will be and the farther and higher it will be able to fly.

Imagine a cannon mounted on the top of a mountain, from which a projectile A is fired with high speed. Such a projectile is capable of flying several kilometers. But in the end, the projectile will still fall to the ground. Its trajectory under the influence of gravity has a curved appearance. Projectile B is fired from the cannon at a higher speed. The trajectory of its flight is more elongated, and it will land much further. The greater the speed of the projectile, the straighter its trajectory becomes and the greater the distance it flies. And, finally, at a certain speed, the trajectory of the projectile C takes the form of a closed circle. The projectile makes one circle around the Earth, another, a third and no longer falls to the Earth. It becomes an artificial satellite of the Earth.

Of course, no one sends cannon shells into space. But spacecraft, which have received a certain speed, become satellites of the Earth.

first cosmic speed

What speed should a spacecraft get in order to overcome the earth's gravity?

The minimum speed that an object must be given in order to put it into a near-Earth circular (geocentric) orbit is called first cosmic speed .

Let us calculate the value of this velocity relative to the Earth.

A body in orbit is subjected to the gravitational force directed towards the center of the Earth. It is also a centripetal force trying to pull this body to the Earth. But the body does not fall to the Earth, since the action of this force is balanced by another force - centrifugal, which tries to push it out. Equating the formulas of these forces, we calculate the first cosmic velocity.

where m is the mass of the object in orbit;

M is the mass of the Earth;

v1 - first space velocity;

R is the radius of the earth

G is the gravitational constant.

M = 5.97 10 24 kg, R = 6,371 km. Consequently, v1 ≈ 7.9 km/s

The value of the first terrestrial cosmic velocity depends on the radius and mass of the Earth and does not depend on the mass of the body put into orbit.

Using this formula, you can calculate the first cosmic velocities for any other planet. Of course, they differ from the first cosmic velocity of the Earth, since celestial bodies have different radii and masses. For example, the first cosmic velocity for the Moon is 1680 km/s.

An artificial Earth satellite puts into orbit space rocket, accelerating to the first cosmic speed and above and overcoming the earth's gravity.

The beginning of the space age

The first space velocity was achieved in the USSR on October 4, 1957. On this day, earthlings heard the call signs of the first artificial satellite Earth. It was launched into orbit with the help of a space rocket created in the USSR. It was a metal ball with antennae, weighing only 83.6 kg. And the rocket itself had enormous power for that time. Indeed, in order to put into orbit only 1 additional kilogram of weight, the weight of the rocket itself had to increase by 250-300 kg. But the improvement of rocket designs, engines and control systems soon made it possible to send much heavier spacecraft into earth orbit.

The second space satellite, launched in the USSR on November 3, 1957, already weighed 500 kg. On board was complex scientific equipment and the first living creature - the dog Laika.

The space age has begun in the history of mankind.

Second space velocity

Under the influence of gravity, the satellite will move horizontally over the planet in a circular orbit. It will not fall to the surface of the Earth, but it will not move to another, higher orbit either. And in order for him to be able to do this, he needs to be given a different speed, which is called second cosmic speed . This speed is called parabolic, runaway speed , release rate . Having received such a speed, the body will cease to be a satellite of the Earth, leave its surroundings and become a satellite of the Sun.

If the speed of the body when starting from the Earth's surface is higher than the first cosmic velocity, but lower than the second one, its near-Earth orbit will have the shape of an ellipse. And the body itself will remain in near-Earth orbit.

A body that, when starting from the Earth, has received a speed equal to the second cosmic velocity, will move along a trajectory that has the shape of a parabola. But if this speed even slightly exceeds the value of the second space velocity, its trajectory will become a hyperbola.

The second cosmic velocity, like the first one, has a different meaning for different celestial bodies, since it depends on the mass and radius of this body.

It is calculated by the formula:

Between the first and second cosmic velocity, the ratio is preserved

For the Earth, the second escape velocity is 11.2 km/s.

For the first time, a rocket that overcame gravity was launched on January 2, 1959 in the USSR. After 34 hours of flight, she crossed the orbit of the moon and entered interplanetary space.

The second space rocket towards the Moon was launched on September 12, 1959. Then there were rockets that reached the surface of the Moon and even made a soft landing.

Subsequently, the spacecraft went to other planets.