The state of weightlessness in terrestrial conditions. What is weightlessness from the point of view of a physicist and an astronaut? See what “Weightlessness” is in other dictionaries

Burning a candle on Earth (left) and in zero gravity (right)

Weightlessness- a state in which there is no force of interaction between a body and a support or suspension (body weight), arising in connection with gravitational attraction or the action of other mass forces (in particular, the force of inertia that occurs during accelerated movement of the body).

Sometimes the term is used as a synonym for the name of this phenomenon microgravity, which is incorrect (it gives the impression that gravity is absent or negligibly small).

Causes

The state of weightlessness occurs when the external forces acting on the body are only mass (gravitational forces), or the field of these mass forces is locally homogeneous, that is, the field forces impart to all particles of the body in each position the same acceleration in magnitude and direction (which when moving in the Earth's gravitational field practically takes place if the dimensions of the body are small compared to the radius of the Earth), or the initial velocities of all particles of the body are the same in magnitude and direction (the body moves translationally).

For example, a spacecraft and all the bodies in it, having received the appropriate initial speed, move under the influence of gravitational forces along their orbits with almost the same accelerations as free ones; neither the bodies themselves nor their particles exert mutual pressure on each other, that is, they are in a state of weightlessness. At the same time, in relation to the cabin of the device, the body located in it can remain at rest in any place (freely “hang” in space). Although gravitational forces during weightlessness act on all particles of the body, there are no external surface forces that could cause mutual pressure of particles on each other.

Thus, any body whose dimensions are small compared to the earth’s radius, performing a free forward motion in the Earth's gravitational field, will, in the absence of others external forces, be in a state of weightlessness. The result will be similar for the movement in the gravitational field of any other celestial bodies.

Story

The change in the weight of a ball when it falls freely in a liquid was noted by Leibniz. In 1892-1893 several experiments demonstrating the occurrence of weightlessness during free fall were carried out by Moscow State University professor N.A. Lyubimov, for example, a pendulum removed from its equilibrium position during free fall did not swing.

Features of human activity and technology

In conditions of weightlessness on board a spacecraft, many physical processes (convection, combustion, etc.) proceed differently than on Earth. The absence of gravity, in particular, requires special design of systems such as showers, toilets, food heating systems, ventilation, etc. To avoid the formation of stagnant zones where carbon dioxide can accumulate, and to ensure uniform mixing of warm and cold air, The ISS, for example, has been installed a large number of fans. Eating and drinking, personal hygiene, working with equipment and, in general, ordinary everyday activities also have their own characteristics and require the astronaut to develop habits and the necessary skills.

The effects of weightlessness are inevitably taken into account in the design of a liquid-propellant rocket engine designed to launch in zero gravity. Liquid fuel components in tanks behave exactly the same as any liquid (forming liquid spheres). For this reason, the supply of liquid components from the tanks to the fuel lines may become impossible. To compensate for this effect, a special tank design is used (with gas and liquid media separators), as well as a fuel sedimentation procedure before starting the engine. This procedure consists of turning on the ship's auxiliary engines for acceleration; the slight acceleration they create upsets liquid fuel at the bottom of the tank, from where the supply system directs fuel into the lines.

Impact on the human body

During the transition from the conditions of the presence of body weight at the Earth’s surface to conditions of weightlessness (primarily when leaving spaceship into orbit), most astronauts experience a body reaction called space adaptation syndrome.

When a person stays in space for a long time (more than a week), the lack of body weight begins to cause certain harmful changes in the body.

The first and most obvious consequence of weightlessness is the rapid atrophy of muscles: the muscles are actually turned off from human activity, as a result, all the physical characteristics of the body decrease. In addition, the consequence of a sharp decrease in the activity of muscle tissue is a reduction in the body's oxygen consumption, and due to the resulting excess hemoglobin, the activity of the bone marrow that synthesizes it (hemoglobin) may decrease.

There is also reason to believe that limited mobility will disrupt phosphorus metabolism in the bones, which will lead to a decrease in their strength.

Weight and gravity

Quite often the disappearance of weight is confused with the disappearance of gravitational attraction, but this is not true at all. An example is the situation on the International Space Station (ISS). At an altitude of 350 kilometers (the altitude of the station), the acceleration due to gravity is 8.8/², which is only 10% less than on the surface of the Earth. The state of weightlessness on the ISS does not arise due to the “lack of gravity,” but due to movement in a circular orbit at the first escape velocity, that is, the cosmonauts seem to constantly “fall forward” at a speed of 7.9 km/s.

Weightlessness on Earth

On Earth, for experimental purposes, a short-term state of weightlessness (up to 40 s) is created when an aircraft flies along a ballistic trajectory, that is, the trajectory along which the aircraft would fly under the influence of the force of gravity alone. This trajectory at low speeds turns out to be a parabola, which is why it is sometimes mistakenly called “parabolic”. In general, the trajectory is an ellipse or hyperbola.

Such methods are used to train astronauts in Russia and the USA. In the cockpit, a ball is suspended on a string, which usually pulls the string down (if the plane is at rest or moving uniformly and in a straight line). The lack of tension in the thread on which the ball hangs indicates weightlessness. Thus, the pilot must control the plane so that the ball hangs in the air without tension on the string. To achieve this effect, the plane must have a constant acceleration equal to g and directed downward. In other words, pilots create zero g-force. Such an overload can be created for a long time (up to 40 seconds) by performing a special aerobatic maneuver called “failure in the air.” Pilots abruptly begin to climb, entering a “parabolic” trajectory, which ends with the same sharp drop in altitude. Inside the fuselage there is a chamber in which future cosmonauts train; it is a completely upholstered passenger cabin without seats to avoid injuries both in moments of weightlessness and in moments of overload.

A person experiences a similar feeling of (partial) weightlessness when flying on civil aviation flights during landing. However, for flight safety reasons and due to the heavy load on the aircraft structure, any scheduled aircraft drops altitude, making several long spiral turns (from a flight altitude of 11 km to an approach altitude of about 1-2 km). That is, the descent is carried out in several passes, during which the passenger feels for a few seconds that he is slightly lifted up from the seat. The same feeling is experienced by motorists who are familiar with routes passing along steep hills when the car begins to slide down from the top.

According to the law of universal gravitation, all bodies are attracted to each other, and the force of attraction is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between them. That is, the expression “absence of gravity” makes no sense at all. At an altitude of several hundred kilometers above the Earth's surface - where manned spacecraft and space stations fly - the Earth's gravitational force is very strong and practically no different from the gravitational force near the surface.

If it were technically possible to drop an object from a tower 300 kilometers high, it would begin to fall vertically and with the acceleration of free fall, just as it would fall from the height of a skyscraper or from the height of a person. Thus, during orbital flights, the force of gravity is not absent or weakened to a significant extent, but is compensated. In the same way as for watercraft and balloons, the force of gravity of the earth is compensated Archimedean force, and for winged aircraft - the lifting force of the wing.

Yes, but the plane flies and does not fall, and the passenger inside the cabin does not fly like astronauts on the ISS. During a normal flight, the passenger feels his weight perfectly, and what keeps him from falling to the ground is not the direct lifting force, but the ground reaction force. Only during an emergency or artificially caused sharp decline does a person suddenly feel that he stops putting pressure on the support. Weightlessness arises. Why? But because if the loss of height occurs with an acceleration close to the acceleration of free fall, then the support no longer prevents the passenger from falling - she herself falls.

spaceref.com It is clear that when the plane stops sharply descending, or, unfortunately, falls to the ground, then it will become clear that gravity has not gone away. For in terrestrial and near-Earth conditions, the effect of weightlessness is possible only during a fall. Actually, a long fall is an orbital flight. A spacecraft moving in orbit at escape velocity is prevented from falling to Earth by the force of inertia. The interaction of gravity and inertia is called “centrifugal force,” although in reality such a force does not exist, it is in some way a fiction. The device tends to move in a straight line (tangentially to the near-Earth orbit), but the Earth's gravity constantly “spins” the trajectory of movement. Here, the equivalent of gravitational acceleration is the so-called centripetal acceleration, as a result of which it is not the value of the speed that changes, but its vector. And therefore the speed of the ship remains unchanged, but the direction of movement is constantly changing. Since both the spacecraft and the astronaut are moving at the same speed and with the same centripetal acceleration, the spacecraft cannot act as a support on which the weight of a person presses. Weight is the force of a body acting on a support that arises in the field of gravity and prevents it from falling. But a ship, like a sharply descending airplane, does not prevent it from falling.

That is why it is completely wrong to talk about the absence of Earth’s gravity or the presence of “microgravity” (as is customary in English-language sources) in orbit. On the contrary, the gravity of the earth is one of the main factors in the phenomenon of weightlessness that occurs on board.

We can talk about true microgravity only when applied to flights in interplanetary and interstellar space. Far from a large celestial body, the gravitational forces of distant stars and planets will be so weak that the effect of weightlessness will arise. We have read more than once in science fiction novels about how to deal with this. Space stations in the form of a torus (steering wheel) will spin around a central axis and create an imitation of gravity using centrifugal force. True, in order to create the equivalent of gravity, you will have to give the torus a diameter of more than 200 m. There are other problems associated with artificial gravity. So all this is a matter of the distant future.

In space, weightlessness is a constant condition of life and activity. This sharply distinguishes space from the environment in which humanity lives. On Earth, a person constantly struggles with the force of gravity, so the loss of his own weight is unusual for him, and a person has no experience of being in weightlessness.

Yes, you can occasionally experience weightlessness: for example, while flying on an airplane, when it falls into “air pockets” or suddenly loses altitude. Skydivers know the feeling of weightlessness well. Weightlessness- a state in which there is no force of interaction between the body and the support.

In conditions of weightlessness on board a spacecraft, many physical processes (convection, combustion, etc.) proceed differently than on Earth. The absence of gravity requires a special design of systems such as showers, toilets, food heating systems, ventilation, etc. To avoid the formation of stagnant zones where carbon dioxide can accumulate, and to ensure uniform mixing of warm and cold air, the ISS, for example, has a large number of fans installed. Eating and drinking, personal hygiene, working with equipment and, in general, ordinary everyday activities also have their own characteristics and require the astronaut to develop habits and the necessary skills. The effects of weightlessness are taken into account in the design of a liquid-propellant rocket engine designed to launch in zero gravity.

How does weightlessness affect a person?

When transitioning from the conditions of earth's gravity to conditions of weightlessness, most astronauts experience an organism reaction called space adaptation syndrome. The symptoms of this condition are similar to seasickness: loss of appetite, dizziness, headache, increased salivation, nausea, sometimes vomiting, spatial illusions. All these effects usually disappear after 3-6 days of flight. During a long (several weeks or more) stay of a person in space, the lack of gravity begins to cause certain changes in the body that are negative in nature: rapid muscle atrophy - the muscles are actually turned off from human activity, as a result all the physical characteristics of the body decrease; the consequence of a sharp decrease in the activity of muscle tissue is a reduction in the body’s oxygen consumption; due to the resulting excess hemoglobin, the activity of the bone marrow, which synthesizes hemoglobin, may decrease; limited mobility disrupts phosphorus metabolism in the bones, which leads to a decrease in their strength.

The human body, once in conditions of weightlessness, begins to rebuild. A man is losing weight. The whole body becomes flabby, as if lying in bed for a long time. The bones become fragile - they do not experience stress here. Muscles work little. And from inactivity all organs weaken. It's like a person who has been in bed for several months learning to walk again. Cosmonauts Nikolaev and Sevastyanov, after eighteen days of being in weightlessness, could not get to their feet at first.

To reduce the harmful effects of weightlessness, scientists have come up with various means: they recommend that astronauts do more physical exercise in space, mainly with expanders. We created special “penguin” load-bearing suits for astronauts. These tight-fitting suits have elastic bands sewn into them that tighten the body into a tight ball. To stay upright in such a suit, you have to slightly tense your muscles all the time. And this is exactly what is needed so that they do not weaken.

They also make a “treadmill” at orbital stations. In order not to float away, the astronaut fastens himself with elastic bands. They replace the astronaut’s weight, pull him by the belt and shoulders down to the floor, and press him to the “track.” She runs back under the astronaut. And he runs forward along it. Not everyone easily tolerates weightlessness, especially at first. Many people feel like they have been hung upside down. Some people experience nausea. The first day or two, astronauts usually get used to weightlessness.

Weightlessness occurs when a spacecraft enters orbit. But the disappearance of weight should not be confused with the disappearance of gravitational attraction - for example, on the International Space Station (at an altitude of 350 km) it is only 10% less than on Earth. The state of weightlessness on the ISS arises not due to the lack of gravity, but due to movement in a circular orbit at the first escape velocity, that is, the cosmonauts seem to constantly “fall forward” at a speed of 7.9 km/s.

How astronauts are trained in zero gravity on Earth

On Earth, for experimental purposes, it is possible to create a short-term state of weightlessness (up to 40 seconds) when an aircraft flies along a parabolic trajectory. To achieve this effect, the aircraft must have a constant downward acceleration g (zero g). Such an overload can be created for a long time (up to 40 seconds) by performing a special aerobatics maneuver (“failure in the air”). The pilots sharply lower the altitude; at a standard flight altitude of 11,000 meters, this gives the required 40 seconds of “weightlessness”; Inside the fuselage there is a chamber in which future cosmonauts train; it has a special soft coating on the walls to avoid injuries when climbing and dropping altitude. A person experiences a feeling similar to weightlessness when flying on civil aviation flights upon landing. But for reasons of flight safety and heavy load on the aircraft structure civil Aviation drops altitude gradually, making several long spiral turns (from a flight altitude of 11 km to an approach altitude of about 1-2 km). Those. The descent is carried out in several passes, during which the passenger only feels for a few seconds that he is being lifted up from the seat. The state of weightlessness can be felt at the initial moment of free fall of a body in the atmosphere, when air resistance is still small.

Weight as the force with which any body acts on a surface, support or suspension. Weight arises due to the gravitational attraction of the Earth. Numerically, the weight is equal to the force of gravity, but the latter is applied to the center of mass of the body, while the weight is applied to the support.

Weightlessness - zero weight, can occur if there is no gravitational force, that is, the body is sufficiently away from massive objects that can attract it.

The International Space Station is located 350 km from Earth. At this distance, the acceleration of gravity (g) is 8.8 m/s2, which is only 10% less than on the surface of the planet.

This is rarely seen in practice - gravitational influence always exists. Astronauts on the ISS are still affected by the Earth, but there is weightlessness there.

Another case of weightlessness occurs when gravity is compensated by other forces. For example, the ISS is subject to gravity, slightly reduced due to distance, but the station also moves in a circular orbit at escape velocity and centrifugal force compensates for gravity.

Weightlessness on Earth

The phenomenon of weightlessness is also possible on Earth. Under the influence of acceleration, body weight can decrease and even become negative. The classic example given by physicists is a falling elevator.

If the elevator moves downward with acceleration, then the pressure on the elevator floor, and therefore the weight, will decrease. Moreover, if the acceleration is equal to the acceleration of gravity, that is, the elevator falls, the weight of the bodies will become zero.

Negative weight is observed if the acceleration of the elevator movement exceeds the acceleration of gravity - the bodies inside will “stick” to the ceiling of the cabin.

This effect is widely used to simulate weightlessness in astronaut training. The aircraft, equipped with a training chamber, rises to a considerable height. After which it dives down along a ballistic trajectory, in fact, the machine levels off at the surface of the earth. When diving from 11 thousand meters, you can get 40 seconds of weightlessness, which is used for training.

There is a misconception that such people perform complex figures, like the “Nesterov loop,” to achieve weightlessness. In fact, modified production passenger aircraft, which are incapable of complex maneuvers, are used for training.

Physical Expression

The physical formula for weight (P) during accelerated movement of a support, be it a falling bodice or a diving aircraft, is as follows:

where m is body mass,
g – free fall acceleration,
a is the acceleration of the support.

When g and a are equal, P=0, that is, weightlessness is achieved.

More details about what it is and where it can be felt will be discussed in this article.

Static

There are two types of weightlessness. This is static - observed when moving away from an object with a large mass. For example, a body that has flown a considerable distance from the planet. It should be understood that its weight does not completely disappear.

The fact is that gravity from massive objects such as planets and stars, although it decreases with distance, does not completely disappear. Its action extends infinitely far to all corners of the Universe, inversely proportional to the square of the distance. This follows from the definition of weightlessness.

Thus, it is impossible to leave the zone of influence of the gravitational field.

Dynamic

Another type of weightlessness is dynamic. It is constantly experienced by astronauts and pilots. You can neutralize the effect of the gravitational field of a massive object by freely falling onto it. To do this, it is necessary for the object to gain a certain speed and become a satellite.

Having gained the required speed, the satellite begins to enter a state of constant free fall. Objects inside it will be in a state of weightlessness. This speed is called the first cosmic speed.

For planet Earth, for example, the speed is about 8 kilometers per second. For the Sun - already 640. Everything depends on the mass of the object and its density. In those where the density reaches hundreds of millions of tons per cubic centimeter, the cosmic speed approaches the speed of light.

Weightlessness on Earth

It turns out that you can experience the state of weightlessness without leaving the planet. True, for a very short period. For example, a passenger in a car driving on a curved bridge will experience weightlessness for a while at the top of the bridge's camber.

Passengers traveling to public transport on a bumpy road, they constantly experience the effects of weightlessness every time the bus hits a hole or bump. For a short period of time they are in a state of free fall.

Entertainment

Recently, special testing grounds have appeared in the entertainment industry, where everyone can experience weightlessness.

After passing a medical examination and paying a certain amount of money, you can get on board a plane that flies along a wave-like trajectory, and during the dive people can experience an unusual feeling of weightlessness for half a minute.

The pilot of the plane, through the intercom, reports the beginning of weightlessness. This is necessary for security reasons. The fact is that after a free fall the plane rapidly gains altitude. At the same time, people on board experience the diametrically opposite effect - overload.

Sometimes this value reaches three times the acceleration of gravity. In other words, your body weight in zero gravity will be three times its natural weight. If you fall from a height of several meters with such a body weight, you can very easily get injured.

For these purposes, specially trained instructors sit on board the aircraft in the zero-gravity compartment. Their task is to promptly lower to the floor of the plane those people who did not manage to meet the given time interval.

A series of ups and downs occurs at intervals of up to twenty times during one aircraft flight.

In Russia, for example, for those who want to experience weightlessness, there is a special centrifuge, which is located in the center for training cosmonauts and pilots. Again, after a medical examination and a monetary contribution of about 55 thousand rubles, a person can experience the effects of weightlessness.

Effect on the human body

By definition, weightlessness is absolutely harmless to the human body. Difficulties begin when it lasts several days, weeks or months.

In most cases, this only applies to the inhabitants of space stations. Cosmonauts who have been on board spacecraft for a long time begin to experience significant discomfort. This is primarily due to the vestibular mechanism.

On Earth, under normal conditions, the otoliths of the vestibular apparatus press on the nerve endings, thus telling our brain where is up and down, orienting the human body in space.

Weight and weightlessness

It's a completely different matter when the body weighs nothing. All processes in it proceed differently. Due to the lack of otolith pressure, spatial orientation is disrupted. The concept of “up” and “down” completely disappears in space. The absence of physical activity. In this condition muscle will atrophy if no measures are taken. With its degradation, it also suffers bone. When there is no load, less phosphorus enters the bones of the body.

There are difficulties with eating and swallowing liquids. All liquids tend to take on a spherical shape, which makes everyday things very difficult. Even an ordinary runny nose in conditions of weightlessness can be a very difficult test for the body due to the fact that sputum is not eliminated under the influence of gravity, but forms spherical drops.

To maintain the necessary tone, astronauts constantly train for several hours a day. When going to bed, they tie themselves with special straps so as not to get injured while sleeping.

To feed astronauts, special food in tubes and bread that does not crumble have been developed.

Before long time To experience weightlessness, a person must feel its effect on earth in order to find out how the absence of gravity will affect him in the future.