# Helpless in zero G

2011-04-19

It occurred to me the other day that people would be incredibly helpless in a large, zero-gravity environment. If you managed to become stationary, out of reach from any walls or objects, you would effectively be stranded, screaming for someone to come collect you.

Unless you have some kind of rocket motor with you, you are dependent on being able to push off of things to control your movement. Also, zero gravity could involve other unpleasant elements. For instance, if you push off from one surface too aggressively, all you can do it wait until you crunch into the far wall. There would be no particularly effective way to reduce your rate of movement, though you could try splaying yourself out like a sky-diver trying to descend slowly.

This somewhat alters my sense of how much fun a huge recreational space station would be.

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Matt April 19, 2011 at 6:25 pm

You may find that your own gravitational interaction with your surroundings may be sufficient to prevent you from “getting stuck.” I haven’t tried calculating whether or not this is true, although the math isn’t that hard.

Milan April 19, 2011 at 6:27 pm

You could also expel saliva or urine in order to create a crude reaction engine.

Tristan April 19, 2011 at 11:38 pm

The gravitational interaction with your surroundings would be miniscule. GMm/r^2

If you weighed 100kg, and the space station was such that there was zero mass on one side and 1 million kg on the other side, with 5 meters between – the resulting force is 0.000266904 newtons.

But it doesn’t matter, because it would be impossible to get stuck because air resistance reduces towards zero as your speed reduces. The only way you could get “stuck” is if you caught an object of the right mass moving in the opposite direction, but then you could simply push off of it to get going again.

Matt April 20, 2011 at 12:03 am

Nice job on investigating my apparently ill-conceived claim.

Milan April 20, 2011 at 7:32 am

The only way you could get “stuck” is if you caught an object of the right mass moving in the opposite direction, but then you could simply push off of it to get going again.

You could collide with another person in such a way that you both lost almost all your momentum but still kept moving past each other slowly. Then, air resistance might be enough to stop you.

Tristan April 20, 2011 at 2:04 pm

“Then, air resistance might be enough to stop you.”

This would be true if the resistant force created by the drag were constant with respect to speed – you would decelerate at a roughly constant rate and arrive at a stop. Just like a car rolling along the ground at a low speed decelerated slowly and linearly to a stop.

However, air resistance is not constant – it decreases exponentially as your speed decreases. Therefore the resistant force will continue to reduce as you approach zero. So you don’t decelerate at a linear rate, but in such a way that as you decelerate you begin decelerating slower and slower.

And, even if you did stop with respect to the wind, for that to be “stopped” with respect to your environment, the air in the space station would have to be static. But no one will want to live in a stuff space station, so there will always be some amount of wind cased by circulation.

Matt April 20, 2011 at 2:12 pm

You could almost certainly “swim” away if you were patient enough. Flapping your arms quickly in one direction and slowly bringing them back up should suffice.

Milan April 24, 2011 at 1:05 pm

Even getting stranded for a few minutes while ‘swimming’ would take some of the fun out of zero gravity. Clearly, the human system of locomotion didn’t evolve to cope with zero gravity environments.

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