Weightlessness in a gravitational field
Astronauts float inside the satellite while orbiting around the earth.Why? Is there no gravity overthere? The answer is "No". Artifical satellites are at the height of 300km to 400km from the surface of earth. The gravity is not only present, but it is the only unbalanced force which is enabling a sattelite to orbit the earth. Artificial satellite is under a single force i.e it is accelerating. If gravity is present overthere then what is the reason behind the weightlessness of astronauts?
To understand this we have to re-visit our concepts about:
- What is weight?
- What type of force is it?
- How it can be measured?
Let us find the answers of these questions.
If a person is sitting on a chair, earth's gravitational force is pulling him downwards, towards the centre of the earth which is called his weight. The chair is also exerting an upward force which is sometimes referred to, as a normal reaction force, it results from the contact between the chair and the person bottom end. The gravitational force is not a contact force and called field (gravitational) force, while the normal reaction force cannot be exerted on the person until a contact is made by the person and the chair. The other example of a contact force is frictional force.
Without a contact force ( normal reaction force) ther is no means of feeling or measuring the non contact or action at a distance force ( the force of gravity in this case). Weight can be measured indirectly by a scale or balance. In normal circumstances when a body and a balance are in equilibrium, the normal reaction force is equal to the weight of a body. If either balance or body are not in equilibrium or even both of them are not in equilibrium, normal reaction force
is not equal to the the weight of a body.
The scenario which was explained above helps us to understand why astronauts feel weightlessness.If a body is accelerating, it is not in equilibrium its weight will be different to its actual weight. The value of new weight let say it apparent weight depends upon the magnitude and the direction of the acceleration of a body.
If a body is accelerating upwards its apparent weight will be greater than its actual weight.
If a body is accelerating downwards its apparent weight will be less than its actual weight.
If body is falling freely ( g=9.8ms2) there will be no upward reaction force, the sensation of weightlessnes can be experienced.
Finally we have concluded that astronauts experience weightlessness because they are falling freely along with the satellite while orbitting around the earth.
Reference:
https://www.wired.com/2008/09/gravity-weightlessness-and-apparent-weight/
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