# Movement under weightless conditions **URL:** \ **Category:** Factual Questions\ **Created:** [September 30, 2015, 6:26pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062 "2015-09-30T18:26:02Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![halman](https://avatars.discourse-cdn.com/v4/letter/h/5f9b8f/32.png) [@halman](https://boards.straightdope.com/u/halman)\ **Post date:** [October 4, 2015, 5:54am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/21 "2015-10-04T05:54:36Z")
> [@theonemacduff](#): > > I’ve been trying to figure out how fast a person could move inside a space station when essentially they are “swimming” through an atmosphere. Swimmers can apparently go a max of about 1.6m per sec., but that’s a sprinting speed, and everyday movement would be a good deal slower. There’s the added complication that under conditions of weightlessness, one is also, in effect, friction free, thus, one could launch oneself and then only need to use energy to come to a halt, without crashing into a bulkhead too too heavily. To be honest, I’m not even sure there is a question here, but it’s been puzzling me for a while, and I’d be interested in the thoughts of others; by oneself, one tends to get stuck in ruts of thought, like a plough that never turns. > > I did several searches on the boards for this question, but nothing popped, hence the fresh thread. Movement in zero gravity is not done by ‘swimming’, as air offers practically no resistance at low speeds. Large airfoils are needed to move enough air to actually move your body. According to some science fiction writers, being stuck in the middle of a large enclosed space would require throwing some mass away from you to start yourself moving in the opposite direction. Like clothing. For the most part, moving in zero-gravity is difficult, because your body constantly reacts differently from what you expect. Pushing with one hand will make you spin around instead of moving away from what you pushed against. Trying to turn a wrench will make you spin around instead of the nut, unless you are properly braced. ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 4, 2015, 7:33am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/22 "2015-10-04T07:33:08Z")
One nasty problem this creates is how do you create a video game that models this correctly? If you don’t give players a magical jetpack, and they have to control the game using existing technology - a couple joysticks or about 6 keyboard keys - how would you do it? Handhold movement is easy. Plenty of video games model this just fine. Shove a thumbstick or WASD, and the astronaut moves to the handhold in the corresponding direction. But if you want to leap across a gap, how do you tell the game “jump to this handhold”. What if a player doesn’t want to go for a handhold and just wants to gently let go and float there? Etc. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 4, 2015, 8:29am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/23 "2015-10-04T08:29:33Z")
It should be possible to move youself by blowing air from your mouth. Inhaling air is less directioal than blowing it out through pursed lips. (If that seems difficult to accept, consider that the exhaust from a jet engine is a narrow, fast, long column of gases, but the intake is not. It woukd be tedious to propel youself that way, but if you were stuck in the middle of a space, it ought to work. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 4, 2015, 2:25pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/24 "2015-10-04T14:25:29Z")
The average human male has a 5 liter lung capacaty and can exhale at a maximum pressure of 2.1 psig (0.0145 MPa[SUB]gage[/SUB]) for about two seconds. Air is 1.19 g/L, giving a mass flow rate of about q = 3 g/s. Assume an effective velocity of approximately 0.5 m/s (experimentally measured using sophisticated aparatust consisting of a length of USB cable and a Post-It wind vane). Ignoring the expansion term in the Tsiolkovsky rocket equation, the force developed is around 0.0015 N and the total impulse from a single breath is 0.003 N-s. The resulting change in velocity is a miniscule ~4.3 x 10[SUP]-6[/SUP] m/s. (Note that I’ve used dry air in the calculation; exhaled air will be at saturation and will actually be less dense. There is also no way you’ll exhale the entire volume of the lung at peak pressure; average pressure of exhalation is 0.3 to 0.5 psi.) Even if you ignore the velocity loss from breathing in (adding back the 6 g of air per breath) and form drag from displacing the air in front of you, trying to jet yourself around by breathing air isn’t going to make an ant’s piss worth of difference. Stranger ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 4, 2015, 8:12pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/25 "2015-10-04T20:12:15Z")
OK, now keep on breathing for an hour, and see how far that force gets you. It’s not practical as an everyday means of getting around, but it is enough to keep you from starving to death if you’re stranded in a large area. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 4, 2015, 8:18pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/26 "2015-10-04T20:18:04Z")
> [@Chronos](#): > > OK, now keep on breathing for an hour, and see how far that force gets you. It’s not practical as an everyday means of getting around, but it is enough to keep you from starving to death if you’re stranded in a large area. If you exhale at full force continuously for an hour you’re going to end up with a pulmanory embolism. Stranger ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [October 4, 2015, 8:26pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/27 "2015-10-04T20:26:50Z")
> [@MikeS](#): > > Yup, [it’s been done;](https://www.youtube.com/watch?v=BTkFIE_-kL8) the brief shot of pigeons in weightlessness starts around 1:10. As you predicted, the birds seem generally disoriented, though if they were up there for long enough they might learn to compensate. I wonder how a hummingbird would do under such conditions. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [October 4, 2015, 8:38pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/28 "2015-10-04T20:38:14Z")
> [@Stranger\_On\_A\_Train](#): > > …trying to jet yourself around by breathing air isn’t going to make an ant’s piss worth of difference. Which begs the question, if you were an ant, how much momentum could you build up just by pissing? ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 4, 2015, 8:58pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/29 "2015-10-04T20:58:09Z")
> [@leahcim](#): > > Which begs the question, if you were an ant, how much momentum could you build up just by pissing? Ants don’t actually pee. Waste, in the form of a gelatinous mass is concentrated and excreted through the Malpighian tubes that exit in the forward postpetiole region. Stranger ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [October 4, 2015, 11:03pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/30 "2015-10-04T23:03:19Z")
> [@Mangetout](#): > > It should be possible to move youself by blowing air from your mouth. Inhaling air is less directioal than blowing it out through pursed lips. > > (If that seems difficult to accept, consider that the exhaust from a jet engine is a narrow, fast, long column of gases, but the intake is not. So astronauts could solve their motion problem by eating lots of beans, and farting their way across the space station? But that might upset those behind you, and lead to personal disagreements among residents on the space station. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 5, 2015, 12:55am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/31 "2015-10-05T00:55:25Z")
> [@t-bonham@scc.net](#): > > … and lead to personal disagreements among residents on the space station. So! I see you beans and raise you some cabbage!!! … an hour later … Houston, we’ve had a problem. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 5, 2015, 2:27am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/32 "2015-10-05T02:27:01Z")
No, no, no… Canned beans and buttermilk. Absolutely nothing but those two items on the spaceship, in every nook, cranny, and storage closet, in unmarked cans. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [October 5, 2015, 2:32am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/33 "2015-10-05T02:32:43Z")
I wonder… You could get yourself spinning around an axis the length of your body by movement of your arms. Could you then convert the rotational momentum to momentum along that axis? Divers use movement of their arms, bending and twisting the body to rotate in various ways. Changing spin and body angle. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 5, 2015, 2:54am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/34 "2015-10-05T02:54:22Z")
Not without contacting “the ground” or some other object to transfer momentum. If you could convert rotational momentum directly to linear momentum, you’d be able to create a (locally) inertialess thruster. The general concept of translating rotational momentum to linear momentum has been proposed many times, typically invoking some vague conception of Mach’s principle and transfer of momentum to the global field, but there is no practical mechanism to make this work. Stranger ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 5, 2015, 6:22am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/35 "2015-10-05T06:22:41Z")
> [@Stranger\_On\_A\_Train](#): > > If you exhale at full force continuously for an hour you’re going to end up with a pulmanory embolism. > > Stranger I’m not suggesting anyone exhale at full force, nor am I suggesting _blowing_ as a means of routine locomotion - inhaling normally and exhaling through pursed lips should still provide a little impulse, and the only thing working against it is air resistance. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [October 5, 2015, 10:59am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/36 "2015-10-05T10:59:16Z")
You could try blowing a balloon up and releasing it. Hey- you could blow hundreds of them up and release them one after the other. You can get about a metre a second out of a deflating balloon. What is the ratio of mass between a human and a balloon? -googles- -a party balloon apparently weighs 1.3g. A hundred would weigh 0.13 kg. A human weighs around 70kg. So a hundred uninflated balloons weighs about 0.0018 as much as a human. Inflate a party pack of 100 party balloons and you might get about 1.8 centimetres per second of velocity change if you let them off in rapid succession. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 5, 2015, 11:02am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/37 "2015-10-05T11:02:57Z")
> [@](#): > > Quoth **Kedikat** : > > I wonder… > You could get yourself spinning around an axis the length of your body by movement of your arms. Only for so long as you keep on moving your arms. Stop windmilling your arms, and your rotation will also stop. Like linear momentum, you can’t change your angular momentum without interacting with something else. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [October 5, 2015, 9:33pm UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/38 "2015-10-05T21:33:59Z")
> [@MikeS](#): > > Yup, [it’s been done;](https://www.youtube.com/watch?v=BTkFIE_-kL8) the brief shot of pigeons in weightlessness starts around 1:10. As you predicted, the birds seem generally disoriented, though if they were up there for long enough they might learn to compensate. That video has iffy descriptions. It says that cats have an automatic reflex action to rotate under gravity, which is lost under weightlessness. That reflex action is volitional - the cats choose to rotate to get their feet oriented under themselves. You can see the cats fighting to figure out which way to rotate, and spinning around depending on which way they are moving. ---
**Author:** ![ssgenius](https://avatars.discourse-cdn.com/v4/letter/s/b5ac83/32.png) [@ssgenius](https://boards.straightdope.com/u/ssgenius)\ **Post date:** [October 6, 2015, 2:27am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/39 "2015-10-06T02:27:51Z")
Interesting discussion. If an astronaut got caught in the middle of a big space away from any walls or holds and was stopped and motionless. Could they get going again without any assistance ? My thought would be to throw a boot or 2 to get moving again (but at a slow speed) but at least they would be moving ---
**Author:** ![Habeed](https://avatars.discourse-cdn.com/v4/letter/h/a587f6/32.png) [@Habeed](https://boards.straightdope.com/u/Habeed)\ **Post date:** [October 6, 2015, 4:40am UTC](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062/40 "2015-10-06T04:40:41Z")
I wonder what you could use as a jetpack to do maintenance in a station like this. It would be a massive, pressurized volume, but in zero G because it wouldn’t be practical to spin it up. You might be able to work on large spacecraft in a shirt sleeves environment. Maybe you could fuel it with a bottle of compressed hydrogen + interior air? [Previous page](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062.md?page=1) [Next page](https://boards.straightdope.com/t/movement-under-weightless-conditions/733062.md?page=3)