The science
Here on Earth, we take gravity for granted. However, the force of gravity, by which objects are drawn towards each other in proportion to their mass, is much greater than an apple falling on Newton's head. Below are the strangest facts about this universal force.
It's all in our head
The force of gravity is a constant and consistent phenomenon, but our perception of this force is not so. According to a study published in April 2011 in the journal PLoS ONE, people are able to make more accurate judgments about falling objects while sitting.
The researchers concluded that our perception of gravity is based less on the actual visual direction of the force and more on the "orientation" of the body.
The findings could lead to a new strategy to help astronauts cope with microgravity in space.
Hard descent to the ground
The experience of astronauts has shown that the transition from a state of weightlessness and back can be very difficult for the human body. In the absence of gravity, muscles begin to atrophy, and bones also begin to lose bone mass. According to NASA, astronauts can lose up to 1 percent of their bone mass per month.
Upon returning to earth, astronauts' bodies and minds need a period of time to recover. Blood pressure, which in space becomes equal throughout the body, should return to normal functioning, in which the heart works well and the brain receives enough food.
Sometimes the restructuring of the body has an extremely difficult effect on astronauts, both physically (fainting repeatedly, etc.) and emotionally. For example, one astronaut told how, upon returning from space, he broke a bottle of aftershave lotion at home, because he forgot that if he released it into the air, it would fall and break, and would not float in it.
To lose weight, "try Pluto"
On this dwarf planet, a person weighing 68 kilograms would weigh no more than 4.5 kg.
On the other hand, on the planet with the highest level of gravity, Jupiter, the same person would weigh about 160.5 kg.
A person will probably also feel like a feather on Mars, since the force of gravity on this planet is only 38 percent of that on earth, that is, a 68-kilogram person will feel how light his gait is, since he will only weigh 26 kg.
Different gravity
Even on earth, gravity is not the same everywhere. Due to the fact that the shape of the globe is not an ideal sphere, its mass is distributed unevenly. Therefore, uneven mass means uneven gravity.
One mysterious gravity anomaly is observed in Hudson Bay in Canada. This region has lower gravity than others, and a 2007 study identified the cause as melting glaciers.
The ice that once covered this area during the last Ice Age has long since melted, but the Earth is not completely free of its burden. Since the gravity of an area is proportional to the mass of that region, and the "glacial trail" has pushed aside some of the earth's mass, gravity has become weaker here. Minor crustal deformation explains 25-45 percent of the unusually low gravitational force, and is also blamed on the movement of magma in the Earth's mantle.
Without gravity, some viruses would be stronger
Bad news for space cadets: Some bacteria become unbearable in space.
In the absence of gravity, the activity of at least 167 genes and 73 proteins changes in bacteria.
Mice that ate food with such salmonella got sick much faster.
In other words, the danger of infection doesn't necessarily come from outer space; it's more likely that our own bacteria are gaining strength to attack.
Black holes at the center of the galaxy
So named because nothing, not even light, can escape their gravitational pull, black holes are among the most destructive objects in the universe. At the center of our galaxy is a massive black hole with the mass of 3 million suns. Sounds scary, doesn't it? However, according to experts from Kyoto University, this black hole is currently “just resting.”
In fact, a black hole does not pose a danger to us earthlings, since it is very far away and behaves extremely calmly. However, in 2008 it was reported that the hole was sending out bursts of energy about 300 years ago. Another study published in 2007 found that several thousand years ago, a "galactic hiccup" sent a small amount of material the size of Mercury into this very hole, resulting in a powerful explosion.
This black hole, named Sagittarius A*, has a relatively fuzzy shape compared to other black holes. "This weakness means that stars and gas rarely get too close to the black hole," says Frederick Baganoff, a postdoctoral fellow at the Massachusetts Institute of Technology. "There is a huge appetite, but it is not being satisfied."
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.
Despite the fact that gravity is the weakest interaction between objects in the Universe, its significance in physics and astronomy is enormous, since it can influence physical objects at any distance in space.
If you are interested in astronomy, you have probably wondered what such a concept as gravity or the law of universal gravitation is. Gravity is the universal fundamental interaction between all objects in the Universe.
The discovery of the law of gravity is attributed to the famous English physicist Isaac Newton. Probably many of you know the story of the apple that fell on the head of the famous scientist. However, if you look deeper into history, you can see that the presence of gravity was thought about long before his era by philosophers and scientists of antiquity, for example, Epicurus. However, it was Newton who first described the gravitational interaction between physical bodies within the framework of classical mechanics. His theory was developed by another famous scientist, Albert Einstein, who in his general theory of relativity more accurately described the influence of gravity in space, as well as its role in the space-time continuum.
Newton's law of universal gravitation states that the force of gravitational attraction between two points of mass separated by a distance is inversely proportional to the square of the distance and directly proportional to both masses. The force of gravity is long-range. That is, regardless of how a body with mass moves, in classical mechanics its gravitational potential will depend purely on the position of this object at a given moment in time. The greater the mass of an object, the greater its gravitational field - the more powerful the gravitational force it has. Space objects such as galaxies, stars and planets have the greatest gravitational force and, accordingly, quite strong gravitational fields.
Gravitational fields
Earth's gravitational field
The gravitational field is the distance within which gravitational interaction occurs between objects in the Universe. The greater the mass of an object, the stronger its gravitational field - the more noticeable its impact on other physical bodies within a certain space. The gravitational field of an object is potential. The essence of the previous statement is that if you introduce the potential energy of attraction between two bodies, then it will not change after moving the latter along a closed loop. From here comes another famous law of conservation of the sum of potential and kinetic energy in a closed loop.
In the material world, the gravitational field is of great importance. It is possessed by all material objects in the Universe that have mass. The gravitational field can influence not only matter, but also energy. It is due to the influence of the gravitational fields of such large cosmic objects as black holes, quasars and supermassive stars that solar systems, galaxies and other astronomical clusters are formed, which are characterized by a logical structure.
Recent scientific data show that the famous effect of the expansion of the Universe is also based on the laws of gravitational interaction. In particular, the expansion of the Universe is facilitated by powerful gravitational fields, both of its small and largest objects.
Gravitational radiation in a binary system
Gravitational radiation or gravitational wave is a term first introduced into physics and cosmology by the famous scientist Albert Einstein. Gravitational radiation in the theory of gravitation is generated by the movement of material objects with variable acceleration. During the acceleration of an object, a gravitational wave seems to “break away” from it, which leads to oscillations of the gravitational field in the surrounding space. This is called the gravitational wave effect.
Although gravitational waves are predicted by Einstein's general theory of relativity as well as other theories of gravity, they have never been directly detected. This is due primarily to their extreme smallness. However, in astronomy there is indirect evidence that can confirm this effect. Thus, the effect of a gravitational wave can be observed in the example of the convergence of double stars. Observations confirm that the rate of convergence of double stars depends to some extent on the loss of energy from these cosmic objects, which is presumably spent on gravitational radiation. Scientists will be able to reliably confirm this hypothesis in the near future using the new generation of Advanced LIGO and VIRGO telescopes.
In modern physics, there are two concepts of mechanics: classical and quantum. Quantum mechanics was developed relatively recently and is fundamentally different from classical mechanics. In quantum mechanics, objects (quanta) do not have definite positions and velocities; everything here is based on probability. That is, an object can occupy a certain place in space at a certain point in time. Where he will move next cannot be reliably determined, but only with a high degree of probability.
An interesting effect of gravity is that it can bend the space-time continuum. Einstein's theory states that in the space around a bunch of energy or any material substance, space-time is curved. Accordingly, the trajectory of particles that fall under the influence of the gravitational field of this substance changes, which makes it possible to predict the trajectory of their movement with a high degree of probability.
Theories of gravity
Today scientists know over a dozen different theories of gravity. They are divided into classical and alternative theories. The most famous representative of the former is the classical theory of gravity by Isaac Newton, which was invented by the famous British physicist back in 1666. Its essence lies in the fact that a massive body in mechanics generates a gravitational field around itself, which attracts smaller objects. In turn, the latter also have a gravitational field, like any other material objects in the Universe.
The next popular theory of gravity was invented by the world famous German scientist Albert Einstein at the beginning of the 20th century. Einstein was able to more accurately describe gravity as a phenomenon, and also explain its action not only in classical mechanics, but also in the quantum world. His general theory of relativity describes the ability of a force such as gravity to influence the space-time continuum, as well as the trajectory of elementary particles in space.
Among the alternative theories of gravity, the relativistic theory, which was invented by our compatriot, the famous physicist A.A., perhaps deserves the greatest attention. Logunov. Unlike Einstein, Logunov argued that gravity is not a geometric, but a real, fairly strong physical force field. Among the alternative theories of gravity, scalar, bimetric, quasilinear and others are also known.
- For people who have been in space and returned to Earth, it is quite difficult at first to get used to the strength of the gravitational influence of our planet. Sometimes this takes several weeks.
- It has been proven that the human body in a state of weightlessness can lose up to 1% of bone marrow mass per month.
- Among the planets in the solar system, Mars has the least gravitational force, and Jupiter has the greatest.
- The known salmonella bacteria, which cause intestinal diseases, behave more actively in a state of weightlessness and are capable of causing much more harm to the human body.
- Among all known astronomical objects in the Universe, black holes have the greatest gravitational force. A black hole the size of a golf ball could have the same gravitational force as our entire planet.
- The force of gravity on Earth is not the same in all corners of our planet. For example, in the Hudson Bay region of Canada it is lower than in other regions of the globe.
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 stay on this edge of the abyss only thanks to what affects us Earth's gravitational force; we do not fall from the earth’s surface only 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 gravity of our planet suddenly ceased to act. We would endlessly rush around in the abyss of world space, not knowing either the top or the bottom.
Movement on Earth
to his moving around the Earth we also owe it to gravity. We walk on the Earth and constantly overcome the resistance of this force, feeling its action like some heavy weight on our feet. This “load” especially makes itself felt when climbing uphill, when you have to drag it, like some kind of heavy weights hanging from your feet. It affects us no less sharply when going down the mountain, forcing us to speed up our steps. Overcoming gravity when moving around the Earth. These directions - “up” and “down” - are shown 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 shows “down” for those living in Moscow, shows “up” for residents of Tierra del Fuego. The directions showing "down" for people at the pole and at the equator are right angles; they are perpendicular to each other. Outside the Earth, with distance from it, the force of gravity decreases, as the force of gravity decreases (the force of attraction of the Earth, like any other world body, extends indefinitely far in space) and the centrifugal force increases, which reduces the force of gravity. Consequently, the higher we lift some cargo, for example, in a balloon, the less this cargo will weigh.Earth's centrifugal force
Due to the daily rotation, centrifugal force of the earth. This force acts everywhere on the Earth's surface 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 here, according to Newton’s calculations, the centrifugal force is only 1/289 of the attractive force. The further north you are from the equator, the less centrifugal force. At the pole itself 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 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 Earth's gravity and centrifugal force is called gravity. The force of gravity at all points on the earth's surface would be the same if ours were a perfectly accurate and regular ball, if its mass were the same density everywhere and, finally, if there were no daily rotation around its axis. But, since our Earth is not a regular sphere, does not consist in all its parts of rocks of the same density and rotates all the time, then, consequently, the force of gravity at each point on the earth's surface is slightly different. Therefore, at every point on the earth’s surface the magnitude 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 seem to rest against the Earth's equator, are the largest. Radii that end at the North or South Pole are the smallest. Therefore, all bodies at the equator have less gravity (less weight) than at the pole. It is known that at the pole the gravity is greater than at the equator by 1/289th. This difference in gravity of the same bodies at the equator and at the pole can be determined by weighing them using spring balances. If we weigh bodies on scales with weights, then we will not notice this difference. The scales will show the same weight both at the pole and at the equator; weights, like bodies that are weighed, will also, of course, change in weight.
Spring scales as a way to measure gravity at the equator and at the pole. Let’s assume that a ship with cargo weighs about 289 thousand tons in the polar regions, near the pole. Upon arrival at ports near the equator, the ship with cargo will weigh only about 288 thousand tons. Thus, at the equator the ship lost about a thousand tons in weight. All bodies are held on the earth's surface only due to the fact that gravity acts on them. In the morning, when you get 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 move deeper into the Earth, 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/sec) by approximately five percent. With further deepening, the force of gravity will continuously decrease and at the center of the Earth will be equal to zero.Assumptions regarding the Earth's rotation
Our The earth is spinning makes a full revolution around its axis in 24 hours. Centrifugal force, as is known, increases in proportion to the square of the angular velocity. Therefore, if the Earth accelerates its rotation around its axis by 17 times, then the centrifugal force will increase by 17 times squared, i.e. 289 times. Under normal conditions, as mentioned above, the centrifugal force at the equator is 1/289 of the gravitational force. When increasing 17 times the force of gravity and centrifugal force become equal. The force of gravity - the resultant of these two forces - with such an increase in the speed of the Earth's axial rotation 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 length of the day in this critical case will be approximately 1 hour 25 minutes. With further acceleration of the Earth's rotation, all bodies (primarily at the equator) will first lose their weight, and then will be thrown into space by centrifugal force, and the Earth itself will be torn into pieces by the same force. Our conclusion would be correct if the Earth were an absolutely rigid 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 as the Earth’s rotation accelerates, its surface will have to undergo some deformation: it will begin to compress towards the poles and expand towards the equator; it will take on an increasingly flattened appearance. The length of the radius of the earth's equator will begin to increase and thereby increase the centrifugal force. Thus, bodies at the equator will lose their weight before the Earth’s rotation speed increases 17 times, and a catastrophe with the Earth will occur before the day shortens its duration to 1 hour 25 minutes. In other words, the critical speed of the Earth's rotation will be somewhat lower, and the maximum length of the day will be slightly longer. Imagine mentally that the speed of rotation of the Earth, due to some unknown reasons, will approach critical. What will happen to the earth's inhabitants then? First of all, everywhere on Earth a day will be, for example, about two to three hours. Day and night will change kaleidoscopically quickly. The sun, like in a planetarium, will move very quickly across the sky, and as soon as you have time to wake up and wash yourself, it will already disappear behind the horizon, and night will come to replace it. People will no longer be able to accurately navigate time. No one will know what day of the month it is or what day of the week it is. Normal human life will be disorganized. The pendulum clock 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 or hurry, 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 possible to lift very heavy bodies easily. It won’t be difficult to put a horse, an elephant on your shoulders, or even lift a whole house. Birds will lose the ability to land. A flock of sparrows is circling over a trough of water. They chirp loudly, but are unable to come down. A handful of grain thrown by him would hang above the Earth in individual grains. Let us further assume that the Earth's rotation speed is getting closer and closer to critical. Our planet is greatly deformed and takes on an increasingly flattened appearance. It is likened to a rapidly rotating carousel and is about to throw off its inhabitants. The rivers will then stop flowing. They will be long standing 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 float 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 drop anchor, they will no longer control the rudders of their ships, large and small ships will stand motionless. Here is another imaginary picture. A passenger railway train stands at the station. The whistle has already been blown; the train must leave. The driver took all measures in his power. The fireman generously throws coal into the firebox. Large sparks fly from the chimney of the locomotive. The wheels are turning desperately. But the locomotive stands motionless. Its wheels do not touch the rails and there is no friction between them. There will come a time when people will not be able to go down to the floor; they will stick like flies to the ceiling. Let the speed of the Earth's rotation increase. The centrifugal force increasingly exceeds the force of gravity in its magnitude... Then people, animals, household items, houses, all objects on the Earth, its entire animal world will be thrown into cosmic 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 yet having time to turn into giant accumulations of drops, with its entire thickness of water will be separated from the bottom, along which it will be possible to freely pass from Naples to Algeria. Finally, the speed of rotation will increase so much, the centrifugal force will increase so much, that the entire Earth will be torn apart. However, this cannot happen either. The speed of rotation of the Earth, as we said above, does not increase, but on the contrary, even decreases slightly - however, so little that, as we already know, over 50 thousand years the length of the day increases by only one second. In other words, the Earth now rotates at such a speed that is necessary for the animal and plant world of our planet to flourish under the calorific, life-giving rays of the Sun for many millennia. Friction value
Now let's see what friction matters and what would happen if it were absent. Friction, as you know, has a harmful effect on our clothes: the sleeves of coats wear out first, and the soles of shoes wear out first, since sleeves and soles are most susceptible to friction. But imagine for a moment that the surface of our planet was as if well polished, completely 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 a polished floor it is very difficult to walk and you have to be careful not to fall. But the surface of ice and polished floors still has some friction.
Friction force on ice. If the force of friction disappeared on the surface of the Earth, then indescribable chaos would reign on our planet forever. If there is no friction, the sea will rage forever and the storm will never subside. Sandstorms 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 endlessly spread in the air. In the absence of friction, a body that started to move would never stop. On an absolutely smooth earth's surface, various bodies and objects would forever be mixed in the most diverse directions. The world of the Earth would be ridiculous and tragic if there were no friction and attraction of the Earth. Gravitational force is the force with which bodies of a certain mass located at a certain distance from each other are attracted to each other.
The English scientist Isaac Newton discovered the law of universal gravitation in 1867. 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 directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
The force of gravity 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, while walking in the evening in his parents’ garden. Creative people are constantly in search, and scientific discoveries are not an instant insight, but the fruit of long-term mental work. Sitting under an apple tree, Newton was contemplating another idea, and suddenly an apple fell on his head. Newton understood that the apple fell as a result of the Earth's gravitational force. “But why doesn’t the Moon fall to Earth? - he thought. “This means that there is some other force acting on it that keeps it in orbit.” This is how the famous law of universal gravitation.
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 gravity on the surface of the Earth and in space.
Newton combined these proposed types of gravity. Analyzing Kepler's laws describing the motion of 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 acted upon by forces that obey the same law - the law of universal gravitation.
Newton established that Kepler's laws apply only if there is a force of attraction 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 – mass of the first body;
m 2– mass of the second body;
r – distance between bodies;
G – proportionality coefficient, which is called gravitational constant or constant of universal gravitation.
Its value was determined experimentally. G= 6.67 10 -11 Nm 2 /kg 2
If two material points with mass equal to unit mass are located at a distance equal to unit distance, then they attract with a force equal to G.
The forces of attraction are gravitational forces. They are also called gravitational forces. They are subject to the law of universal gravitation and appear everywhere, since all bodies have mass.
Gravity
The gravitational force near the Earth's surface 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 surface of the Earth 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 smaller than the radius of the Earth, the force of gravity on the Moon is 6 times less than on Earth. On Jupiter, on the contrary, the force of gravity is 2.4 times greater than the force of 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 that's not true.
The force with which the body presses on the support or stretches the suspension is weight. If you remove the support or suspension, the body will begin to fall with the acceleration of free fall under the influence of gravity. The force of gravity is proportional to the mass of the body. It is calculated by the formulaF= m g , Where m- body mass, g – acceleration of gravity.
Body weight may change and sometimes disappear altogether. Let's 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 attracts us are equal. But as soon as the elevator began to move downward with acceleration A , weight and gravity are no longer equal. According to Newton's second lawmg+ P = ma. Р =m g -ma.
From the formula it is clear 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, the acceleration A became negative and the weight increased. Overload sets in.
And if the body moves downward with the acceleration of free fall, then the weight will completely become 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 located near the surface of the Earth.