O’zbekiston respublikasi oliy va o’rta maxsus ta’lim vazirligi mirzo ulug’bek nomidagi o’zbekiston milliy universiteti

Notes
1. as a result of heat - issiqlik natijasida.

2. thus repeating the cycle — shunday qilib, davrni qaytalab.

XI. Check these statemants after reading the text given below

1. 
   The state of weightlessness does not exist when the engine of a space vehicle is working.
   
2. 
   Weightlessness does not depend either on the force of the Earth's gravitation or on the distance from the Earth.
   
3. 
   Gravity appears in space vehicle only when it passes through the medium which offers resistance.
   

WHAT IS WEIGHTLESSNESS?
In all vehicles traveling in space, i e. outside the atmosphere, such as space rockets, artificial satellites and spaceships of the future, there exists — when the engine is not working — a state of weightlessness. This simply means that nothing falls down, everything remains "suspended in air" — in the air of the ship's cabin.

There is much misunderstanding about the phenomenon of weightlessness and misconception as to the reasons for it; For instance some people think that weightlessness is due to the great distance from the Earth, the argument being that according to Newton's law of gravitation there would be practically no force of gravity so far away. This argument is of course misplaced and false. We have to think only of satellites circling the Earth at a distance of a few hundred kilometers. It is obvious that the state of weightlessness may exist close to our globe, in such regions where the gravitational field is practically as powerful as on the surface of the Earth.

Let us take the following examples: at a distance of 600 kilometers from the Earth one kilogram (that is 'the mass of 1 kilogram) weighs 900 grams, while at a distance of 1000 kilometers — only 700 grams; at a distance of thousands of kilometers the reading would become insignificant (at a distance of 20 thousand kilometers 1 kilogram would weigh only 60 grams). Now, as everybody knows, a state of weightlessness exists on artificial satellites circling quite close to the Earth, and indeed even on airplanes flying at an altitude of a few thousand meters (though only for a period of a few seconds). Obviously weightlessness has nothing to do with the distance from the Earth, nor with its force of gravity.

The problem will be simplified, if we keep in mind that we can speak of a body only when there is something to support it. When we are in a lift, its floor supports our weight but if the cables on which the lift is suspended break, and ourselves and the lift shall fall down, we would have no weight inside that lift (i. e.¹ in relation to the cabin floor), although the local gravitational field would remain as powerful as before.

All bodies which move in space are in a state identical to the "falling" lift. A "perfect stale" of weightlessness exists on all artificial satellites, space-stations, space rockets and spaceships, in short, in all "vehicles" moving outside the Earth's atmosphere. They represent bodies in a state of a "free fall"; the fact that the satellites are circling the Earth, and not falling towards it, is immaterial. They are moving freely in Earth's gravitation field, exactly like the "falling" lift.

Inside a space vehicle gravity appears only when it is no more in free fall, i. e. when the engine is working, or when the vehicle passes through the medium which offers resistance. This happens when it enters the atmosphere. Such "artificial gravity" is brought about by acceleration due to the working of an engine, or deceleration (decrease of speed) due to² resistance offered by atmospheric air.

In a word, on board artificial satellites and in all space vehicles weightlessness is due to their free movement in Earth's gravitational field. All bodies not "supported" by the Earth or its atmosphere (i. e. balloons and aircraft) and not accelerated or decelerated are in a state of free fall.

During the first few minutes after the take off — when the engine is still on — a rocket vehicle is being "driven" and gains speed. Every part of the rocket, as well as all objects inside it, are being accelerated due to the "pushing" force of the rocket engine which is called the engine "thrust".

Owing to this force, the engine together with the vehicle body gaing speed and gives a "push" to every object inside the vehicle — thus also to the man in the cabin. When standing on the cabin floor which rises upwards, he will feel — added to his own weight — the pressure of the upwards "accelerating" floor. It means that due to the work of the rocket engine he will feel heavier, i. e. he will weigh more as related to the cabin floor of the rocket vehicle.
Notes
1. i. e.qthat is — shunday

2. due to — ko’ra, asoslanib

3. owing to — ko’ra, asoslanib.