In this article, I would like to disprove the notion that astronauts experience weightlessness in ISS because of the absence of gravity. First off, let us find the acceleration due to gravity experienced by an astronaut on the ISS.
Altitude of the ISS from the surface of the Earth=330km to 410km
Average height from the surface of the Earth=370km
Radius of the Earth=6384km
Distance of the ISS from the centre of the Earth=6754km
We are now going to use the formula,
A=(GM)/r^2
Where, G is the Universal gravitational constant, M is the mass of the Earth,
r is the distance of the object from the Earth’s centre.
A=(6.67384 x 10^-11 x 5.9722 x 10^24)/(6754000)^2
We get,
A=8.738 ms^-2
Thus there is not a big difference between the acceleration due to gravity on the Earth when compared to the Acceleration due to gravity exerted by the Earth on the ISS (enough to cause the acceleration to become negligible).
So the question that arises is: Why do we experience weightlessness while orbiting the Earth?
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| Weightlessness. |
While in orbit the astronauts are in a state of free-fall i.e. they are falling towards the Earth. This is because of the Earth’s gravity that acts as centripetal force. Imagine this: You are in an elevator that is ascending at a constant rate, suddenly all the chords are cut and the elevator is in the state of free-fall. I am not being mathematically rigorous here. Resuming, we are in a state of free-fall as the elevator starts its free-fall but the reason we don’t experience “weight” is there is no other object that is exerting a force on us to make us feel the “weight”. It is true that we do have weight but we just don’t “feel” it! Recall Newton’s Third Law : Every action has an equal and opposite reaction. This reaction is what makes us feel our weight.
In the ISS, we are in a similar state of free-fall that is directed toward the Earth but we never get there! This is because of the centrifugal force experienced by the ISS.
Therefore we do have weight on satellites such as the ISS while in orbit, the only reason behind not experiencing weight is because we don’t have any “opposite reaction” being applied on us when we are experiencing free-fall, as illustrated in the example of the elevator.
By Kartik Thooppal Vasu (PdeP Team Member)
I would like to add something here. While on earth, we are receiving reaction forces on only some 'surfaces' on our body. The other parts of the body are 'supported' by these parts. For example our hands are supported to the main body at the shoulders. But while in free fall, there is this absence of 'support' between one part and another that we 'feel' as weightlessness.
ReplyDeleteYes exactly. Thanks a lot for your view. Cheers! :)
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