Zero gravity means zero friction?

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.

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.

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.