Weightlessness - more precisely, microgravity - is a special state outside the Earth (or any other) gravity, when it is practically not felt, and the astronaut's body is in a state of incessant free fall. Zero gravity can be experienced, for example, in a free-fall elevator or plane (such acrobatic planes are used for training in artificial zero gravity), or in Earth orbit, on the International Space Station. Long-term exposure to zero gravity has a detrimental effect on the physical condition of astronauts, so scientists are studying how to reduce the level of loss of muscle and bone mass in microgravity conditions in order to protect future travelers to Mars and beyond. Literally six months spent in orbit cause irreversible changes in the human body.
Prolonged exposure to zero gravity leads to health problems - this is a fact. For example, people already know that flying astronauts will be able to experience a wide range of medical problems, including muscle wasting, calcium deficiency, impaired cardiopulmonary function, visual impairment, and even weakened immunity. Researchers at the Henry Ford Hospital in Michigan have added another problem to this list - weightlessness has been shown to destroy joints that do not heal even after returning to Earth.
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 enough from massive objects that can attract it.
The International Space Station is located 350 km from the Earth. At such a distance, the acceleration of gravity (g) is 8.8 m / s2, which is only 10% less than on the planet's surface.
In practice, you rarely meet - the gravitational effect always exists. The cosmonauts on the ISS are still affected by the Earth, but weightlessness is present there.
Another case of weightlessness occurs when the force of gravity is compensated by other forces. For example, the ISS is subject to the force of gravity, slightly reduced due to the distance, but the station also moves in a circular orbit with the first cosmic speed 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. A classic example given by physicists is a falling elevator.
If the elevator moves downward with acceleration, then the pressure on the floor of the elevator, and therefore the weight, will decrease. Moreover, if the acceleration is equal to the acceleration of gravity, that is, the lift falls, the weight of the bodies will become zero.
Negative weight is observed if the acceleration of the lift exceeds the acceleration of free fall - the bodies inside "stick" to the ceiling of the car.
This effect is widely used to simulate weightlessness in astronaut training. The plane, equipped with a training camera, climbs to a considerable height. After that, it dives down along a ballistic trajectory, in fact, at the surface of the earth the car is leveled. 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 obtain weightlessness. In fact, for training, modified serial passenger aircraft are used, which are incapable of complex maneuvers.
Physical expression
The physical formula of weight (P) with accelerated movement of the support, whether it is a falling bodice or a diving plane, is as follows:
where m is body weight,
g - acceleration of gravity,
a - acceleration of the support.
When g and a are equal, P = 0, that is, weightlessness is achieved.
What is weightlessness? Floating cups, the ability to fly and walk on the ceiling, to move even the most massive objects with ease - this is the romantic idea of this physical concept.
If you ask an astronaut what weightlessness is, he will tell you how difficult it is during the first week on board the station and how long after returning you have to recover, getting used to the conditions of gravity. The physicist, however, will most likely omit such nuances and reveal the concept with mathematical precision using formulas and numbers.
Definition
Let's start our acquaintance with the phenomenon with the disclosure of the scientific essence of the issue. Physics defines weightlessness as a state of a body when its motion or external forces acting on it do not lead to mutual pressure of particles on each other. The latter always arises on our planet when an object moves or rests: it is pressed by the force of gravity and the oppositely directed reaction of the surface on which the object is located.
The exception to this rule are cases, that is, falling with a speed that gives the body the force of gravity. In such a process, there is no pressure of particles on each other, weightlessness appears. Physics says that the state that occurs in spaceships and sometimes in airplanes is based on the same principle. Weightlessness appears in these vehicles when they move at a constant speed in any direction and are in a state of free fall. An artificial satellite or delivered into orbit using a launch vehicle. It gives them a certain speed, which is maintained after the device turns off its own engines. In this case, the ship begins to move only under the influence of gravity and weightlessness occurs.
Houses
The implications of flying for astronauts don't stop there. After returning to Earth, they have to adapt back to gravity for some time. What is weightlessness for an astronaut who has completed a flight? First of all, it is a habit. Consciousness for some period refuses to accept the fact of the presence of gravity. As a result, there are often cases when the astronaut, instead of putting the cup on the table, simply let go of it and realized the mistake only when he heard the sound of the dishes being broken on the floor.
Nutrition
One of the difficult and at the same time interesting tasks for the organizers of manned flights is to provide astronauts with food that is easily assimilated by the body under the influence of weightlessness in a convenient form. The first experiments did not arouse much enthusiasm among the crew members. Indicative in this regard is the case when the American astronaut John Young, contrary to strict prohibitions, brought on board a sandwich, which, however, they did not eat, so as not to violate the charter even more.
To date, there are no problems with diversity. The list of dishes available for Russian cosmonauts includes 250 items. Sometimes a cargo ship starting at the station will deliver a fresh meal ordered by someone from the crew.
The basis of the diet is all liquid meals, drinks, and purees are packed in aluminum tubes. The containers and shells of products are thought out in such a way as to avoid the appearance of crumbs floating in zero gravity and able to get into someone's eye. For example, cookies are made quite small and covered with a shell that melts in the mouth.
Familiar environment
At stations like the ISS, they try to bring all conditions to the usual terrestrial conditions. These are national dishes on the menu, and the air movement necessary both for the functioning of the body and for the normal operation of the equipment, and even the designation of the floor and ceiling. The latter is, rather, of psychological significance. An astronaut in zero gravity does not care what position to work in, however, the allocation of a conditional floor and ceiling reduces the risk of loss of orientation and facilitates faster adaptation.
Zero gravity is one of the reasons why not everyone is hired as astronauts. Adaptation upon arrival at the station and after returning to Earth is comparable to several times enhanced acclimatization. A person with poor health may not be able to withstand such a load.
We live at a time when flights of spaceships around the Earth, to the Moon and to other planets of the solar system are no longer surprising. We know that during flight, astronauts and all objects on spaceships are in a special state called the state of zero gravity. What is this state and can it be observed on Earth? Weightlessness is a complex physical phenomenon. In order to understand it, you need to remember something from the physics course.
So, by the weight of the body, we mean the force with which the body, due to its attraction to the Earth, presses on the support.
Imagine that the support and the body fall freely. After all, a support is also a body on which gravity acts. What will be the weight of the body in this case: with what force will the body act on the support?
Let's do the experiment. Take a small body and hang it from a spring attached to a fixed support. Under the action of gravity, the body begins to move downward, so the spring is stretched until an elastic force arises in it, which balances the force of gravity. If you cut the thread holding the spring to the body, the spring to the body will fall. You can see that during the fall, the tension of the spring disappears and it returns to its original size.
So what happens? When the spring with the body falls, it remains unstretched. That is, the falling body does not act on the spring falling along with it. In this case, the weight of the body is zero, but the body and the spring fall, which means that the force of gravity is still acting on them.
In the same way, if the body and the support or support on which the body lies fall freely, then the body will stop pressing on the support or support. In this case, the body weight will be zero.
Similar phenomena are observed on spaceships and satellites. The satellite revolving around the Earth, the astronaut and all the bodies that are inside the satellite are in continuous free fall (they seem to fall to the Earth). As a result of this, the bodies, during the fall, do not press on the support and do not stretch the spring. Such bodies are said to be in a state of weightlessness ("no weight", the weight is equal to zero).
Bodies not fixed in the spaceship freely "hover". The liquid poured into the vessel does not press on the bottom and walls of the vessel, therefore it does not flow out through the hole in the vessel. The pendulums of the clock rest in whatever position they were left in. An astronaut does not need any effort to keep an arm or a leg in an extended position. His idea of where is up and where is down disappears. If you tell any body the speed relative to the satellite's cabin, then it will move rectilinearly and uniformly until it collides with other bodies.
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In more detail about what it is and where it can be felt, and will be discussed in this article.
Static
There are two types of weightlessness. It 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, however, 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 get out of the zone of action of the gravitational field.
Dynamic
Another type of weightlessness is dynamic. It is constantly tested by cosmonauts and pilots. The effect of the gravitational field of a massive object can be neutralized by free falling on it. This requires the object to gain a certain speed and become a satellite.
Having gained the required speed, the satellite begins to go into a state of constant free fall. The 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. It all depends on the mass of the object and its density. In such places 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 one can experience the state of weightlessness without leaving the planet. True, for a very short period. For example, a passenger in a car driving over a curved bridge will experience weightlessness for a while at the top of the bridge bulge.
Passengers traveling in public transport on bumpy roads constantly experience the effect of weightlessness every time the bus runs into a hole or bump. They are in free fall for a short period of time.
Entertainment
Recently, special training grounds have appeared in the entertainment industry, where everyone can experience weightlessness.
After passing a medical commission and paying a certain amount of money, you can get on board an airplane that flies along a wave-like trajectory, and during a peak, people can experience an unusual feeling of weightlessness for half a minute.
The pilot of the aircraft through the intercom announces the beginning of the effect of weightlessness. This is for security reasons. The fact is that after a free fall, the plane is rapidly gaining altitude. At the same time, people on board experience a diametrically opposite effect - overload.
Sometimes this value reaches three times the acceleration due to gravity. In other words, the weight of the body in zero gravity will be three times its natural weight. Falling from a height of several meters with such a body weight can be very easily injured.
For these purposes, specially trained instructors sit on board the aircraft in the zero-gravity compartment. Their task is to put those people who did not manage to meet the given time interval to the floor of the plane in time.
A series of ups and downs occurs with a frequency of up to twenty times during one plane flight.
In Russia, for example, for those wishing 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 feel the effect of weightlessness.
Effect on the human body
By definition, weightlessness is absolutely harmless to the human body. Difficulties begin when it lasts for several days, weeks or months.
In most cases, this only applies to the inhabitants of space stations. Astronauts who have been on board for a long time begin to experience significant discomfort. This is primarily due to the vestibular mechanism.
On Earth, under usual conditions, the otoliths of the vestibular apparatus press on the nerve endings, thus prompting our brain where the top and bottom are, orienting the human body in space.
Weight and weightlessness
It's quite another matter when the body weighs nothing. All processes in it proceed differently. Due to the lack of pressure from the otoliths, a violation of orientation in space occurs. The concept of "up" and "down" in space completely disappears. Lack of physical activity also harms the human body. In this state, muscle tissue will atrophy if no measures are taken. Bone tissue also suffers with its degradation. In the absence of load, less phosphorus enters the bones of the body.
Difficulty eating and swallowing fluids. At the same time, all liquids tend to take a spherical shape, which makes everyday things very difficult. Even a common runny nose in zero gravity can be a very difficult test for the body due to the fact that phlegm is not removed by gravity, but form spherical drops.
To maintain the required tone, astronauts constantly train for several hours a day. When going to sleep, they tie themselves with special straps so as not to get injured during sleep.
To feed the astronauts, special food in tubes and bread that does not crumble have been developed.
Before experiencing weightlessness for a long time, a person must feel its effect on the ground in order to find out how the absence of gravity will affect him in the future.
