
Ask HN: Gravity Less Room - curious_fellow
My friend had a very interesting question on gravity. How do we create a room with zero gravity ? I have seen those rooms in NASA and some other space based companies.
I found the below link for reference, thou could not get much out of it.
https:&#x2F;&#x2F;www.scienceabc.com&#x2F;innovation&#x2F;how-does-nasa-create-zero-gravity.html<p>Anyone care to explain ? 
Thanks.
======
gus_massa
If you go inside an elevator with a total opaque door and no windows, and
someone cut the cable (and disable all the other security devices), then it
will began to freefall with you inside. You will feel weightless until the
elevator crashes catastrophically with the bottom of the pit. Don't try this
at home.

So the elevator "simulates" a gravity 0 room. You can think that it is only a
gimmick, but it is actually a very important property of Special Relativity,
so it is "true" gravity 0.
[https://en.wikipedia.org/wiki/Equivalence_principle](https://en.wikipedia.org/wiki/Equivalence_principle)

If you want to do the experiment and survive, you have a few options that are
quite similar in the abstract sense:

* Vomit comet: It's a plane that follows during some time the trajectory of an object during free fall that is a parable. If you wake up when the plane is at the top, it is equivalent to the elevator experiment, but with some additional lateral movement that doesn't matter. (And some wings and jet motors to slow down before it crash with the ground.)

* An space station in orbit: The gravity in the ISS is almost equal to the gravity on the ground. It is in free fall, like the elevator or the plane in the previous experiments. The difference is that the ISS is going so fast that before crashing with the Earth, it reach the "end of the word".

It is easier to explain with a flat finite Earth that has the shape of a disc.
If you are in the center of the flat Earth and throw a ball too fast, it will
fly over the border of the disk and fall and hit the elephant or turtle.

The Earth is actually a sphere [citation needed], so the details are more
difficult, because gravity doesn't always go in the same direction, and there
is no borde at the end of the word. But the idea is similar. If you go too far
to one side, there is not more ground bellow you.

The article explain these examples with more details. Try to read it again.

------
bradknowles
1\. Put people into a swimming pool inside of a model space suit filled with
air. 2\. Add weights to balance out the excess buoyancy caused by the suits
filled with air. 3\. Profit?

~~~
eesmith
The referenced link is for the so-called 'Vomit Comet'.

I don't know what difficulty the OP had in reading it.

The idea is that someone falling feels no weight. At least at the beginning.
Air resistance quickly builds up, causing a feeling of weight.

So, surround the person with an aircraft. The engines compensate for the air
resistance, so inside the plane it feels weightless.

See also [https://en.wikipedia.org/wiki/Reduced-
gravity_aircraft](https://en.wikipedia.org/wiki/Reduced-gravity_aircraft) .

~~~
masonic

      The engines compensate for the air resistance
    

That's not how zero gravity is achieved. It's done by parabolic dives that
result in periods of simulated zero gravity.

~~~
eesmith
From the Wikipedia page I pointed to at
[https://en.wikipedia.org/wiki/Reduced-
gravity_aircraft](https://en.wikipedia.org/wiki/Reduced-gravity_aircraft) :

> The sensation of weightlessness is achieved by reducing thrust and lowering
> the nose to maintain a neutral, or "zero lift", configuration such that the
> aircraft follows a ballistic trajectory, with engine thrust exactly
> compensating for drag.

"air resistance" (my term) = "drag" (WP)

"The engines" (my term) = "engine thrust" (WP)

It seems that I am substantially correct, yes? Or are you picking at the
specific wording I used?

