Why do astronauts float?
And how is it related to falling elevators?
We all know that astronauts who visit space do not feel gravity. How else do you get all the neat spacewalks and the floating globules of water? But, the reason for why this happens is actually a little-known fact.
The Common Explanation
We are told that astronauts float in space because there is no gravity at such high altitudes. This also makes sense.
The International Space Station is approximately 408 kilometers above the atmosphere. We all know that gravity decreases with height. It was in fact shown by Isaac Newton, that gravity obeys a particular pattern: as you increase your distance from Earth (or generally any object) the force of gravity decreases substantially.
We call this zero-g or zero gravity. But this explanation fails to take into account one big thing:
The Moon
The moon is more than 300,000 kilometers away from the Earth. Yet, it does feel gravity and is at orbit around the planet. Compared to that, astronauts are way too closer to be not feeling gravity at all.
So, what exactly is the reason for the astronauts floating in space? For that, we have to conduct a thought experiment.
A Thought Experiment
Albert Einstein, a renowned physicist, devised a thought experiment in 1907. Imagine a man in a falling elevator.
Now, will this falling man feel any weight. Let’s think about what weight exactly is. Contrary to popular belief, weight is not actually mass.. Mass is a measure of how heavy objects are.
Instead weight is just a force exerted on us. Gravity pulls us down. Our chair or floor exerts an opposite force on us. This opposite force is going to be as strong as the force of gravity. But the direction is going to be different. This is just everyday physics, which you may recognize as Newton’s Third Law.
Okay. Coming back to the falling elevator. We know, by courtesy of Galileo, that all objects fall at the same speed under the influence of gravity, no matter how heavy they are.
So, the falling elevator and the man inside it are both falling at the same speed. Now, the man is not touching the floor of the elevator anymore. He is trying to catch up with the floor but he can’t, as it is moving away at the same speed.
The result is that the man is floating now. As he can’t catch up to the floor of the elevator, he does not feel his own weight. So, he feels weightless and will continue to hover around till the elevator finally reaches the ground.
The takeaway here is that any falling objects do not feel weight. If that all sounded somewhat counter-intuitive, don’t fret: it’s supposed to. Just take your time to absorb the concept well.
Orbits
Objects in space are continuously following orbits. Even the moon is on an orbit around the Earth. Orbits are circular and stable paths around a planet or a moon.
Here’s how they work, briefly: The Earth is moving, revolving. If you can set up your craft or satellite in a suitable position and with a suitable speed, you can get it to orbit.
The satellite starts to fall towards the Earth, but due to its high speed, it takes some time to do that. By that time, the Earth has moved a bit, so the satellite sort of misses falling to the Earth. The satellite continues this process until it can no longer able to maintain that suitable speed.
The satellite in orbit is technically falling, just slow enough to go around the Earth entirely, and repeating this process again.
The real solution
So, now we come to the actual explanation of why astronauts float in space.
As I mentioned above, orbits are technically falling trajectories. If an object is falling, it feels no gravitational force, as we concluded from the thought experiment.
The International Space Station, and every other spacecraft carrying humans to space are taking orbits. So, the astronauts in them feel no weight at all.
That is the real reason. Not zero-gravity, but weightlessness caused by them orbiting the Earth.
Hopefully, now you have a much clear understanding of why this phenomenon occurs. This is one of the classic examples in science, when one myth takes a prominent place in public opinion, instead of actual facts.
But, the actual facts are much more fascinating, and I hope this article gave you a sense of that fascination.
This was a pretty unusual one after the previous article in this publication. This was written just as a heads up to one of the classic misconceptions in science. ‘Hard as rocket science’ articles are coming up soon.
This article is part of Einstein’s Cup Of Tea, a physics, math, and astronomy publication.
