# Weightlessness

##### Article

January 27, 2022

Weightlessness is a state in which an object does not experience weight because that object has no suspension or support in that particular state. This is the case during free fall, that is, when no force is exerted on the object except gravity. One does not feel the effects of gravity. The g-force is zero. Standing on the floor or sitting on a chair you are attracted by the gravity of the earth. What you experience as a feeling of weight is the reaction force generated where you are standing or under your buttocks. Without a surface there is no weight and you would feel weightless. As soon as there is a surface again, the state of weightlessness ceases. In everyday language, weight and mass are used interchangeably, although weight results from the combination of mass, gravity and the presence of a substrate that holds things back. Weight is expressed in newtons, the unit of force, while mass is expressed in kilograms. Weightlessness does not mean that you no longer have mass. Inducing weightlessness is used in science to see the influence of gravity on certain processes. During his stay in the International Space Station, André Kuipers conducted experiments on the influence of weightlessness on germinating seeds.

## Weightlessness in a spacecraft

In a spacecraft outside the atmosphere, weightlessness prevails when no rocket engine is running. Objects and astronauts experience the same acceleration as the spacecraft, so they are not pressed against the floor or wall. This is not to say that the gravity is very small: at an altitude of 100 kilometers, the gravity is only 3% lower than on the earth's surface.

## Weightlessness in airplanes

Airplanes can temporarily induce a feeling of weightlessness when you fly up at a high altitude at a steep angle and then put the plane into near-free fall by running the engines at low power. You then imitate the trajectory of a stone thrown at an angle, first slanting upwards with decreasing speed and then again with increasing speed and at an increasingly steep angle downwards (a parabolic trajectory). This technique is used when training astronauts. The aircraft must have the acceleration of gravity g (approx. 9.8 m/s2) in vertical direction. It goes without saying that such training can only last for a short time, a few minutes. To experience weightlessness for a longer period of time, you need to orbit the Earth in a spacecraft.

## Weightlessness in the center of a planet

In the center of a planet, in addition to enormous heat and gigantic pressure (on Earth: 1 million times the air pressure at sea level), you would also experience a feeling of weightlessness. The attractive forces are the same in all directions.

## Weightlessness under water

Under water you can experience weightlessness. As a result, astronauts practice underwater to develop routines that are useful in the weightlessness of space. The person, wrapped in a diving suit, is provided with his tools and possibly with so many extra weights that, when he goes under water, his volume, and thus the buoyancy he experiences there, is exactly in balance with his full weight. He then floats in the water. The difference with "real" weightlessness is the resistance that the water creates with every movement and that other objects, such as iron tools, are not weightless.

## Influence of weightlessness on health

Parts of the vestibular system perceive how the head is directed, in weightless condition this is done by the eyes. General reactions to weightlessness are, often initially hilarity, ma

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