Why weightless spacecraft?
Spacecraft are always weightless. This is because many people think that the force of gravity decreases to zero as a result of moving away from the earth. The facts are different. Newton's law of the gravitational ball says that the force of gravity decreases in proportion to the square of the distance, that is, the force decreases four times when it moves at twice the distance, sixteen times when it moves at four times the distance. So we can easily estimate the force of gravity in a spacecraft. The distance from the center of the earth to the earth's surface is about six thousand kilometers. Suppose a space station orbits the earth and the astronauts live completely weightless. If the height of this space station is approximately four hundred kilometers from the surface of the earth. However, we can easily get out his gravitational force. If the force of gravity decreases at a rate proportional to the distance, then the weight is at least seven percent. But since it decreases in square rate with distance, the weight loss is close to fourteen percent. In other words, if a person weighing 60 kg appears at the same height as the space station, then his weight will be reduced by only 6 kg to around 53 kg! If a person weighing 60 kg thinks he is 53 kg, it is not weightless at all. So the weightless environment that astronauts feel in spacecraft is certainly not due to altitude, there is something else. A very simple example can be given to explain that. We feel a little lighter for a moment at the very beginning as we take the elevator from the tall building. It must have been noticed by many. It can be felt much more intensely when the merry-go-round goes down again. But it’s not just imaginary feeling, then we become really light. If we imagined that the whole elevator could fall down freely by tearing the rope of the elevator, then by that time we would have become completely light or weightless. When astronauts pour a glass of water into a spaceless spacecraft, the water floats or hangs in front of them without falling down. If we pour a glass of water inside a freely read elevator, we will see exactly the same thing. The water is floating in front of us without falling down.
Because in fact the water is falling down at the same speed as we are falling down. So it is more stable than us. No matter how simple the idea of creating a weightless environment inside the elevator by tearing the rope of the elevator freely, no one has ever tried it. But astronauts go through this experience.