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The frictional force acting on a body placed on a horizontal plane is $F=\mu{R}$ where $R$ is the normal reaction and is equal to weight of a body in this case. And $\mu$ is the coefficient of friction. But, if gravity is zero, then is the frictional force zero (ignoring all other friction due to atmosphere etc.)? If friction is zero, then how do astronauts in a spaceship experiencing zero gravity move?

(I saw so many question related to this on this site, but they give explanations on cosmological effects on it. But I here avoid all such effects and I want answer to only this specific question.)

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    $\begingroup$ Are you referring to how astronauts more inside the international space station? $\endgroup$ – fibonatic Oct 10 '15 at 7:40
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    $\begingroup$ The normal reaction is not always equal to gravitational force. consider an inclined plane. We sometimes assume surface to be frictionless. It means $\mu$ is zero, not the normal reaction. $\endgroup$ – GRrocks Oct 10 '15 at 7:51
  • $\begingroup$ @fibonatic yea I'm asking about how they move in such stations where there is no gravity? $\endgroup$ – Muhsin Ibn Al Azeez Oct 10 '15 at 8:06
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The normal reaction force is not necessarily equal to weight. When you jump, you push down on the ground. That pushing force plus your weight result in a normal reaction force larger than your weight, which is why you are propelled off the ground.

For astronauts in a space ship, they can push against a wall to generate the normal force necessary for friction (or traction) to allow them to propel themselves parallel to the wall. They necessarily push themselves away from the wall at the same time, so they would need to use multiple walls to move from one place to another.

If you watch a video of astronauts on the International Space Station, you'll see that every spare section of wall has hand holds to allow for easier movement because of the reduced friction.

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    $\begingroup$ Don't forget that gripping something with your hand is a significant cause of normal force. $\endgroup$ – David Richerby Oct 11 '15 at 8:44
  • $\begingroup$ @DavidRicherby Also true. $\endgroup$ – Mark H Oct 11 '15 at 18:53
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Friction exists in space, just that not in the most familiar cases.

  • Walking or rolling are not normally possible without gravity pushing both bodies in contact with a normal force.
  • However the normal force does not have to be only gravity, it could be caused by pressure or some other force (thrusters, magnetism etc).
  • Fluid flowing through a pipe in space would suffer the same friction as it does on earth against pipe walls , the normal being caused by the fluid pressure.
  • Movement by astrounauts is possible either by pushing on a surface (normal Vector) or by creating the friction for a tangent force by for example:
    • In small halls by pushing against oposite walls, creating the normal force out of the normal force of pushing against both walls.
    • By grabbing on a handrail, the fingers of the closed hand cause the normal force on the railing, causing the friction allowing the astronaut to advance forward.
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Friction occurs only when a body starts or tries to start its motion in contact with another body. In space if two seperate bodies can stay in contact then friction must occur there. Here nothing to do with gravity.

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Yes there is friction in space. Friction and gravity are two different concepts. On earth mostly we experience friction because we are always in contact with earth surface due to gravity and whenever anything is in contact with other surface frictional force will come into picture(static of dynamic friction).

I have done some quick research for you who support my answer. I have shared the links and i hope they help you.

Description in Quora

Point no 5__just a random website on google search

Hope that answers your question. Don't forget to mark it answered if it satisfies you.

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  • $\begingroup$ We experience friction because on earth we are in constant contact with other material media and they try to oppose or help (sometimes) our motion. That media can be air, water, ground etc. Your answer includes some non-scientific terms like " we are glued to earth through gravity". They might not be wrong but it is better to edit and give an idea in "scientific words". Your "we experience friction only when two surfaces come in contact with different velocity and friction" is however wrong since there is something called static friction. $\endgroup$ – SchrodingersCat Oct 10 '15 at 12:34
  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. $\endgroup$ – Jon Custer Oct 10 '15 at 18:46
  • $\begingroup$ @JonCuster This user does not have the necessary reputation for commenting. $\endgroup$ – heinrich5991 Oct 10 '15 at 23:14
  • $\begingroup$ But can on their own posts... Different rules. $\endgroup$ – Jon Custer Oct 11 '15 at 3:42
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There's no friction in space?

Strange how every screw just fell out of the ISS!

What's actually going on is you are looking at the friction between an object and the surface it's resting on, neglecting any other force that might be pushing the surfaces together.

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