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After watching Chris Hadfield make a Space Burrito, I saw his bits and pieces floating away here and there.

Inside the ISS, and any other manned craft, there is Oxygen (and other gases) which is obviously to keep them alive. On Earth, when someone throws a ball, it's not only pulled down by gravity, but is slowed down because of drag.

In space, the ISS is also pulled down towards Earth indefinitely because of Orbital Decay.

If I was to slightly prod that Space Burrito inside a manned ship in any "direction", will it eventually slow down to the point where it's moving relative to the ship itself because of the Oxygen (and again, other gases) which is creating drag against it?
Or will it continue floating until it hits the wall?

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  • $\begingroup$ "will it eventually slow down" Yes, eventually. It would have to be an enormous space craft before it was large enough to prevent an object from hitting the wall, though. $\endgroup$ – Andrew Thompson Jan 4 '15 at 12:57
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    $\begingroup$ Note that the air in the station is continuously ventilated by fans to prevent pockets of carbon dioxide forming, provide some air cooling and to remove excess carbon oxides and replenish it with oxygen. That's also one of the reasons why visiting spacecraft have to remain continuously powered while remaining docked to the station. Pressure due to air circulation wouldn't be great but still sufficient to show on video, such as with long-haired astronauts (e.g. Sunita Williams or Karen Nyberg made some nice video tours of the station). $\endgroup$ – TildalWave Jan 4 '15 at 14:09
  • $\begingroup$ @AndrewThompson Yeah, thats why I said prod, because if you lobbed the thing, it would just pong back and forth. :P $\endgroup$ – user7078 Jan 4 '15 at 21:04
  • $\begingroup$ @TidalWave I know! I've seen those tours and their brilliant in their own ways. Not something you see everyday... $\endgroup$ – user7078 Jan 4 '15 at 21:05
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There is air inside the space station so, yes, anything moving within that air will experience air resistance. Whether that air resistance is enough to stop a thrown object before it hits the wall depends entirely on the object and how hard it is thrown. If the object is very aerodynamic (i.e., experiences little air resistance) and/or is thrown hard, it will hit the wall. If the object is very unaerodynamic and/or is thrown gently, it may well stop before it hits the wall.

Here's an equivalent experiment you could do on earth. If you start throwing burritos around in your kitchen, some of them will hit the floor because of gravity. To take that out of the equation, suppose you have two very tall towers, close enough together that you could throw a burrito from one to the other. The idea is that the ground is so far away that all the interesting stuff will happen before any burrito splats on the pavement. Assume there's no wind.

If you stand on top of one of the towers and throw your burrito horizontally and hard enough it will splat on the other tower. If throw it a little more gently, it will still hit the other tower, but lower down. However, if you throw it significantly more gently, air resistance will slow its horizontal velocity to zero before it reaches the other tower and, from that point, it will fall vertically and splat on the pavement.

Now, suppose that you jumped off your tower at the moment you throw the burrito. Let's assume that you are also a burrito so you both fall at the same rate. What would you see? Well, in the first two cases, you'd see the other burrito moving horizontally away from you, slowing down until it hits the wall. In the third case, you'd see it slow down and eventually stop without hitting the other wall, exactly as Chris Hadfield would see in the ISS. Think about that for a moment but don't forget to open your parachute before you hit the ground.

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    $\begingroup$ "Let's assume that you are also a burrito" - that deserves a thumbs up! $\endgroup$ – ThePlanMan Jan 4 '15 at 13:06
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    $\begingroup$ The stunts above are performed by individuals that are trained professionals. Do not try this at home :-) $\endgroup$ – mins Jan 4 '15 at 13:21
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    $\begingroup$ You answered first, so you get the prize. :P Detailed and fun to read explanation. Thanks for that. $\endgroup$ – user7078 Jan 4 '15 at 13:25
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Yes it experiences drag. The burrito is also experiencing the pull of gravity but due to it's velocity relative to the ISS this would be equal and hence unnoticeable.

Will it hit the wall? That depends on how hard you throw it! You can work out how far it will travel by calculating the drag force and then integrating through time. If it requires a longer distance to stop than the longest inside length of the ISS then it'll hit the wall.

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From the other answers I make out that if the speed changes, the drag force changes quadratically.

Without going into the calculations, I believe that it means the following:

  1. Yes, the air slows down the object, and keeps slowing it down
  2. No, the object does not ever have to stop due to drag force as the decrease in speed decreases too fast.

My intuition:

If the wall is far enough it may never be reached, but the object will keep moving forever.


It would be nice if someone could expand or refute this answer with a calculation.

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    $\begingroup$ Yes, the drag force varies as a function of velocity. So, in theory, a gently thrown burrito would neither stop nor reach the wall (Zeno was kinda right after all). However, all of this assumes that everything is continuous. In the real world, once the burrito has slowed to some tiny, tiny velocity, a collision with a single air molecule would be enough to stop it or even reverse its direction. Equations such as "drag is quadratic wrt velocity" are fine at a large scale but they treat air as an idealized fluid, not a bunch of molecules. (continues) $\endgroup$ – David Richerby Jan 5 '15 at 10:19
  • $\begingroup$ This works essentially by averaging the effect of the individual molecular collisions. At large scales, this is fine but, at small scales, the random variation ("noise") in the actual collisions is no longer negligible and may actually be the dominant effect. $\endgroup$ – David Richerby Jan 5 '15 at 10:21

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