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Why don't we ever see astronauts on space walks, or floating 'weightless' in the ISS, adjusting their orientation by rotating their arms like we do instinctively when about to lose our balance and fall backwards head over heels. Would it work? How about adjusting one's orientation by rotating a hand in a circle over one's head and/or moving a hand in a horizontal circle in front of one's chest and consequently one's body rotating the opposite way around a vertical axis? Or by twiddling one's thumbs for a very long time?

I'm thinking that conservation of angular momentum should make this work. It would be a great physics lesson to see it, if it worked.

Could a space ship be turned around by the crew running or walking in a circle inside it? How about by a crew member sitting on the outside of the ship and whirling a mass on a long string?

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We do not see astronauts in the ISS adjusting their orientation by rotating their arms , because it is much simpler to rotate themselves by pushing off the walls of the compartment, they are in. Rotating themselves, using just their body and arms is much more strenuous and hence not very efficient.

But it can be done, somewhat like how a cat rotates itself while falling using just the contortions of its body. You can see an astronaut demonstrating how he can rotate himself in space in this video https://youtu.be/VJcno_XL4RU?t=43

Even better example is this video as suggested by OP in comments https://youtu.be/7ZPVg3qD07g?t=127

Regarding if the spaceship can be turned around by its crew walking and running around, of course theoretically it can be done. But obviously, the scale and mass of the spaceship compared to that of a few humans makes it nearly impossible to do in practice.

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    $\begingroup$ I vaguely recall that the Hubble telescope initially had an aiming problem which was traced to the angular momentum of its magnetic-tape data recorder. A small angular momentum, but a precision system. $\endgroup$
    – rob
    Apr 15 at 16:38
  • $\begingroup$ @rob I couldn't find anything about the Hubble data recorder, but I did find this similar scenario regarding the Voyager spacecraft, but it seems (unfortunately?... it would have been a great story to pique students' interest in angular momentum) to be a myth: space.stackexchange.com/q/10223/40252 $\endgroup$ Apr 19 at 8:58
  • $\begingroup$ The YouTube video is fascinating. The astronaut certainly does seem to do a lot strenuous work to change his orientation only slightly. But I suspect this is because he is not doing it right. $\endgroup$ Apr 19 at 9:01
  • $\begingroup$ youtube.com/watch?v=7ZPVg3qD07g from two minutes in to two minutes forty in shows an astronaut who seems to have got it down. $\endgroup$ Apr 22 at 20:21

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