The state of weightlessness of the body on the artificial satellite is caused. State of weightlessness. How to simulate weightlessness on Earth
Weightlessness, state of a material body in which the forces acting on it external forces or the movement it makes does not cause mutual pressure of the particles on each other. If a body is at rest in the Earth's gravitational field at horizontal plane, then the force of gravity and the reaction of the plane directed in the opposite direction act on it, resulting in mutual pressure of the particles of the body on each other. Human body perceives such pressures as a feeling of weight. A similar result occurs for a body that is in an elevator moving vertically downward with acceleration a¹ g, Where g- acceleration of gravity. But when A =g the body (all its particles) and the elevator fall in free fall and do not exert any mutual pressure on each other; as a result, the phenomenon of N occurs here. In this case, gravity forces act on all particles of a body in a state of N., but there are no external forces applied to the surface of the body (for example, support reactions) that could cause mutual pressure of particles on each other friend. A similar phenomenon is observed for bodies placed in artificial satellite Earth (or spaceship); these bodies and all their particles, having received the corresponding initial speed together with the satellite, move under the influence of gravitational forces along their orbits with equal accelerations, as if free, without exerting mutual pressure on each other, i.e., they are in the H state. As in a body in an elevator, they are acted upon by the force of gravity, but there are no external forces applied to the surfaces of the bodies that could cause mutual pressure of the bodies or their particles on each other.
In general, a body under the influence of external forces will be in a state of gravity if: a) the acting external forces are only mass (gravitational forces); b) the field of these mass forces is locally homogeneous, that is, the field forces impart acceleration to all particles of the body in each position that are identical in magnitude and direction; c) the initial velocities of all particles of the body are identical in magnitude and direction (the body moves translationally). Thus, any body whose dimensions are small compared to the Earth’s radius, performing free translational motion in the gravitational field of the Earth, will, in the absence of other external forces, be in the state H. The result will be similar for the movement in the gravitational field of any other celestial tel.
Due to the significant difference between the conditions of N. and the terrestrial conditions in which instruments and assemblies of artificial Earth satellites, spacecraft and their launch vehicles are created and debugged, the problem of N. occupies an important place among other problems of astronautics. This is most significant for systems that have containers partially filled with liquid. These include propulsion systems with liquid-propellant rocket engines, designed for repeated activation during space flight conditions. Under N conditions, the liquid can occupy an arbitrary position in the container, thereby disrupting the normal functioning of the system (for example, the supply of components from fuel tanks). Therefore, to ensure the start of liquid propulsion systems under N conditions, the following are used: separation of liquid and gaseous phases in fuel tanks using elastic separators (for example, on the Mariner station); fixing part of the liquid at the intake device with a grid system (Agena rocket stage); creating short-term overloads (artificial “heaviness”) before turning on the main propulsion system with the help of auxiliary rocket engines, etc. The use of special techniques is also necessary for separating the liquid and gaseous phases under low-level conditions in a number of system units life support, in fuel cells of the power supply system (for example, collection of condensate by a system of porous wicks, separation of the liquid phase using a centrifuge). Mechanisms of spacecraft (for opening solar panels, antennas, for docking, etc.) are designed to operate in N conditions.
N. can be used to carry out certain technological processes that are difficult or impossible to implement under terrestrial conditions (for example, obtaining composite materials with a uniform structure throughout the entire volume, obtaining bodies of precise spherical shape from molten material due to surface tension forces, etc.). The first experiment on welding various materials under low and vacuum conditions was carried out during the flight of the Soviet spacecraft Soyuz-6 (1969). A number of technological experiments (on welding, studying the flow and crystallization of molten materials, etc.) were carried out at the American orbital station Skylab (1973).
It is especially important to take into account the uniqueness of the conditions of N. during the flight of manned spacecraft: the living conditions of a person in the state of N. differ sharply from the usual earthly ones, which causes changes in a number of his vital functions. So, N. puts the central nervous system and receptors of many analyzer systems (vestibular apparatus, muscular-articular apparatus, blood vessels) under unusual operating conditions. Therefore, N. is considered as a specific integral stimulus that acts on the human and animal body throughout the entire orbital flight. The response to this stimulus is adaptive processes in physiological systems; the degree of their manifestation depends on the duration of N. and, to a much lesser extent, on individual characteristics body.
With the onset of N.'s condition, some astronauts experience vestibular disorders. Long time a feeling of heaviness in the head area persists (due to increased blood flow to it). At the same time, adaptation to N. occurs, as a rule, without serious complications: in N. a person maintains working capacity and successfully performs various work operations, including those that require fine coordination or large expenditures of energy. Motor activity in the N state requires much less energy expenditure than similar movements under weight conditions. If no preventive measures were used during the flight, then in the first hours and days after landing (the period of readaptation to earthly conditions), a person who has completed a long space flight experiences the following set of changes. 1) Impaired ability to maintain a vertical posture in static and dynamic conditions; a feeling of heaviness of parts of the body (surrounding objects are perceived as unusually heavy; there is a lack of training in dosing muscle efforts). 2) Violation hemodynamics during work of medium and high intensity; Pre-fainting and fainting states are possible after moving from a horizontal to a vertical position (orthostatic tests). 3) Disorders of metabolic processes, especially water-salt metabolism, which is accompanied by relative dehydration of tissues, a decrease in the volume of circulating blood, and a decrease in the content of a number of elements in the tissues, in particular potassium and calcium. 4) Violation of the body’s oxygen regime during physical activity. 5) Reduced immunobiological resistance. 6) Vestibulo-vegetative disorders. All these changes caused by N. are reversible. Accelerated restoration of normal functions can be achieved through physiotherapy and exercise therapy, as well as the use of medications. The adverse effects of N. on the human body during flight can be prevented or limited using various means and methods (muscle training, electrical stimulation of muscles, negative pressure applied to the lower half of the body, pharmacological and other means). In a flight lasting about 2 months (the second crew on the American Skylab station, 1973), a high preventive effect was achieved mainly due to the physical training of the astronauts. High-intensity work, which caused an increase in heart rate to 150-170 beats per minute, was performed on a bicycle ergometer for 1 hour a day. Restoration of circulatory and respiratory function occurred in the astronauts 5 days after landing. Changes in metabolism, stato-kinetic and vestibular disorders were mild.
An effective means is likely to be the creation of artificial “heaviness” on board the spacecraft, which can be obtained, for example, by constructing the station in the form of a large rotating (i.e., non-translationally moving) wheel and placing work areas on its “rim.” Due to the rotation of the “rim”, the bodies in it will be pressed against its side surface, which will play the role of a “floor”, and the reaction of the “floor” applied to the surfaces of the bodies will create artificial “gravity”. The creation of even a small artificial “heaviness” on spaceships can prevent the adverse effects of N. on the body of animals and humans.
To solve a number of theoretical and practical problems of space medicine, laboratory methods of modeling N. are widely used, including limiting muscle activity, depriving a person of the usual support along the vertical axis of the body, reducing hydrostatic blood pressure, which is achieved by keeping a person in a horizontal position or at an angle (head below the legs), long-term continuous bed rest or immersion of a person for several hours or days in a liquid (so-called immersion) environment.
Lit.: Kakurin L.I., Katkovsky B.S., Some physiological aspects of long-term weightlessness, in the book: Results of Science. Series Biology, v. 8, M., 1966; Medical and biological research in zero gravity, M., 1968; Physiology in space, trans. from English, M., 1972.
S. M. Targ, E. F. Ryazanov, L. I. Kakurin.
What is weightlessness? Floating cups, the ability to fly and walk on the ceiling, and move even the most massive objects with ease - such 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 it takes to recover after returning, getting used to the conditions of gravity. A physicist, most likely, will omit such nuances and reveal the concept with mathematical precision using formulas and numbers.
Definition
Let's begin our acquaintance with the phenomenon by revealing scientific essence question. Physicists define weightlessness as a state of a body when its movement or external forces acting on it do not lead to mutual pressure of particles on each other. The latter always occurs on our planet when an object moves or is at rest: it is pressed by gravity and the oppositely directed reaction of the surface on which the object is located.
An exception to this rule is cases of falling at the speed that gravity imparts to the body. In such a process there is no pressure of particles on each other, weightlessness appears. Physics says that the condition that occurs in spaceships and sometimes in airplanes is based on the same principle. Weightlessness appears in these devices when they move with constant speed in any direction and at the same time 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.
At home
The consequences of flights for astronauts do not 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 his flight? First of all, it's a habit. Consciousness for some period still refuses to accept the fact of the presence of gravity. As a result, there are often cases when an astronaut, instead of putting a cup on the table, simply let it go and realized the mistake only after hearing the sound of dishes breaking 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 digestible 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 American astronaut John Young, despite strict prohibitions brought a sandwich on board, which, however, they did not eat, so as not to violate the regulations even more.
Today there are no problems with diversity. The list of dishes available to Russian cosmonauts includes 250 items. Sometimes a cargo ship departing for the station will deliver a fresh meal ordered by one of the crew.
The basis of the diet is All liquid dishes, drinks, and purees are packaged in aluminum tubes. The packaging and packaging of products is designed in such a way as to avoid the appearance of crumbs that float in weightlessness and could get into someone’s eye. For example, cookies are made quite small and covered with a shell that melts in your mouth.
Familiar surroundings
At stations like the ISS, they try to bring all conditions to those familiar on Earth. These include national dishes on the menu, air movement necessary both for the functioning of the body and for the normal operation of equipment, and even the designation of the floor and ceiling. The latter has, rather, psychological significance. An astronaut in zero gravity does not care in what position to work, however, the allocation of a conditional floor and ceiling reduces the risk of loss of orientation and promotes faster adaptation.
Weightlessness is one of the reasons why not everyone is accepted as an astronaut. Adaptation upon arrival at the station and after returning to Earth is comparable to acclimatization, enhanced several times. A person with poor health may not be able to withstand such a load.
Today, perhaps even people know about the fact that weightlessness is observed in space. Small child. Such widespread this fact served as inspiration for numerous science fiction films about space. However, in reality, few people know why there is weightlessness in Space, and today we will try to explain this phenomenon.
False Hypotheses
Most people, having heard the question about the origin of weightlessness, will easily answer it by saying that such a state is experienced in Space for the reason that the force of gravity does not act on bodies there. And this will be a completely wrong answer, since the force of gravity acts in Space, and it is this force that holds all cosmic bodies in their places, including the Earth and the Moon, Mars and Venus, which inevitably revolve around our natural luminary - the Sun.
Having heard that the answer is incorrect, people will probably pull out another trump card from their sleeves - the absence of an atmosphere, the complete vacuum observed in Space. However, this answer will not be correct either.
Why is there weightlessness in space?
The fact is that the weightlessness experienced by astronauts on the ISS arises due to a whole combination of various factors.
The reason for this is that the ISS orbits the Earth at a tremendous speed exceeding 28 thousand kilometers per hour. This speed affects the fact that the astronauts on the station cease to feel Earth’s gravity, and a feeling of weightlessness is created relative to the ship. All this leads to the fact that the astronauts begin to move around the station exactly as we see in science fiction films.
How to simulate weightlessness on Earth
It is interesting that the state of weightlessness can be artificially recreated within the Earth’s atmosphere, which, by the way, is being successfully done by specialists from NASA.
NASA has such an aircraft on its balance sheet as the Vomit Comet. This is a completely ordinary airplane, which is used to train astronauts. It is he who is able to recreate the conditions of being in a state of weightlessness.
The process of recreating such conditions is as follows:
- The airplane sharply gains altitude, moving along a pre-planned parabolic trajectory.
- Reaching the top point of the conventional parabola, the airplane begins a sharp downward movement.
- Due to sudden change trajectory, as well as the downward thrust of the aircraft, all people on board begin to be in conditions of weightlessness.
- Having reached a certain point of descent, the airplane levels its trajectory and repeats the flight procedure, or lands on the surface of the Earth.
The weight of a body is the force with which the body, due to the attraction of the Earth, presses on a fixed (relative to the Earth) horizontal support or tensions the suspension thread. Body weight equal to force gravity.
Since the support or suspension, in turn, acts on the body, a characteristic sign of weight is the presence of deformations in the body caused by its interaction with the support or suspension.
When bodies fall freely, there are no deformations in them; in this case, the bodies are in state of weightlessness. The figure shows a setup that can be used to detect this. The installation consists of spring scales from which a load is suspended. The entire installation can move up and down on guides.
If the scales with the load fall freely, then the scale pointer is at zero, which means that the scale spring is not deformed.
Let's analyze this phenomenon using the laws of motion. Let us assume that a mass suspended on a spring moves downward with acceleration a. Based on Newton's second law, we can say that it is acted upon by a force that is equal to the difference between the forces P and F, where P is the force of gravity and F is the elastic force of the spring applied to the load. So,
ma = P - F or ma = mg - F
F = m (g - a)
When the load is in free fall, a = g and, therefore,
F - m (g - a) = 0
This indicates the absence of elastic deformations in the spring (and in the load).
The state of weightlessness occurs not only during free fall, but also during any free flight of a body when only gravity acts on it. In this case, the particles of the body do not act on the support or suspension and do not receive acceleration relative to this support or suspension under the influence of gravity towards the Earth.
If the installation shown in the figure is forced to move freely upward with a sharp tug on the rope, then the scale indicator will stand at zero during such a movement. And in this case, the scales and the load, moving upward with the same acceleration, do not interact with each other.
So, if only gravity acts on bodies, then they are in a state of weightlessness, a characteristic feature of which is the absence of deformations and internal stresses.
The state of weightlessness should not be confused with the state of a body under the influence of balanced forces. So, if a body is inside a liquid, the weight of which in the volume of the body is equal to the weight of the body, then the force of gravity is balanced by the buoyant force. But the body will put pressure on the liquid (as on a support), as a result of which the stresses caused in it by the force of gravity will not disappear, but This means that it will not be in a state of weightlessness.
Let us now consider the weightlessness of bodies on artificial Earth satellites. When a satellite flies freely in orbit around the Earth, the satellite itself and all the bodies on it, in the reference system associated with the Earth’s center of mass or with the “fixed” stars, move with the same acceleration at any given moment in time. The magnitude of this acceleration is determined by the gravitational forces acting on them towards the Earth (the gravitational forces towards other cosmic bodies can be ignored, they are very small). As we have seen, this acceleration does not depend on the mass of the body. Under these conditions, there will be no interaction between the satellite and all the bodies located on it (as well as between their particles) due to gravity towards the Earth. This means that during the free flight of the satellite, all the bodies in it will be in a state of weightlessness.
The bodies not secured in the satellite ship, the astronaut himself floats freely inside the satellite; liquid poured into a vessel does not press on the bottom and walls of the vessel, so it does not flow out through the hole in the vessel; plumb lines (and pendulums) are at rest in any position in which they are stopped.
The astronaut does not need any effort to keep his arm or leg in an inclined position. His idea of where is “up” and where is “down” disappears.
If you give a body speed relative to the satellite cabin, then it will move rectilinearly and uniformly until it collides with other bodies.
To eliminate possible dangerous consequences the effects of the state of weightlessness on the life activity of living organisms, and above all humans, scientists are developing various ways creating artificial “gravity”, for example by giving future interplanetary stations a rotational motion around the center of gravity. The elastic force of the walls will create the necessary centripetal acceleration and cause deformations in the bodies in contact with them, similar to those they had under Earth conditions.
Body weight R is the force with which a body, due to its attraction to the Earth, acts on a horizontal support or stretches a suspension thread. Body weight should not be confused with its mass. Mass is measured in kilograms, and weight, like any force, is measured in newtons. Mass is a scalar quantity (has no direction), weight is a vector quantity (has direction).
The weight of a body is numerically equal to the force of gravity if it is on a support at rest relative to the Earth or suspended on a thread stationary relative to the Earth (i.e. in an inertial reference frame). If the support or suspension together with the body moves rapidly up or down, then the weight of the body will differ from the force of gravity, i.e. P≠ mg.
Force N acting on given body from the side of the support perpendicular to its surface is called normal ground reaction force .
If a body lies on a stationary support, then two forces act on it: the reaction force of the support and the force of gravity (Fig. 2.5).
Based on Newton's second law, and since the body is at rest, its acceleration is . Therefore, and . This means that the modules of these forces are equal: N=mg. The weight of a body P is a force that counteracts, according to Newton’s third law, the force of normal pressure N. Then N = P and P = mg.
If the support or suspension together with the body moves rapidly up or down, then the weight of the body will differ from the force of gravity.
Let's consider three cases.
· If the support or suspension together with the body moves upward with uniform acceleration or
down equally slow (acceleration in both cases is directed upward, a> 0), then
P = m(g+ A),
those. body weight is greater than gravity P > mg. The state of a body in which its weight exceeds the force of gravity is called overload .
Overload is characterized quantitatively by the ratio, which is denoted by the letter n and is called load factor.
The shorter the duration of the overload, the greater the magnitude of the overload a person can withstand. Thus, it has been established that a person, being in an upright position, tolerates overloads quite well from 8g for 3s to 5g for 12-15s. With an instantaneous action, when they last less than 0.1 s, a person is able to endure twenty-fold and even greater overloads.
In the acceleration section of the launch vehicle, the load factor is several units.
· If the support or suspension together with the body moves downward with equal acceleration or upward with equal deceleration (acceleration in both cases is directed downward, A< 0), then
P=m(g- A),
those. body weight is less than gravity P< mg.
· At A= g . P =0, i.e. the body does not press on the support. The state of a body in which its weight is zero is called weightlessness.
Any freely falling body is in a state of weightlessness. To experience this state, it is enough to take a simple jump. After turning off the engines, when spaceship enters orbit around the Earth, its acceleration becomes equal to the acceleration of free fall, and the astronaut in orbital space station will be in a state of equilibrium.
Each body of mass m located on the Earth is attracted to the Earth under the influence of a gravitational force directed towards its center and equal to
(M is the mass of the Earth, R is the distance from the body to its center (near the surface of the Earth this distance is approximately equal to its radius R 3).
If this body lies on a stationary support, then two forces act on it: the reaction force of the support N and the gravitational force F. These two forces give a resultant force F n directed perpendicular to the axis of rotation (Fig. 1.17):
The resultant force Fn, according to Newton’s second law, causes normal (centripetal) acceleration, i.e.
Taking into account that υ= ωr, we find
Therefore, Fn, has maximum value at the equator and F n =0 at the poles. Therefore, at all points earth's surface, except for the poles, the weight of the body P is less than the gravitational force F. However, in a number of practical problems, we can neglect the daily rotation of the Earth and assume that the weight of the body P is equal to the force of gravity.