Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is there friction in space?

  1. Nov 24, 2014 #1
    As you know there is vacuum in space. So when there is a vacuum there cant be friction. For friction to happen gas should be there in the space. Is there gas in space and is that the reason why there is friction or not in space?
  2. jcsd
  3. Nov 24, 2014 #2
    There's gas and dust, but the density is extremely low and as such the friction effects are usually negligible.
  4. Nov 24, 2014 #3
    There is definitely gas and dust in space, but the densities are incredibly low. Around black holes, gas and dust falling into it are pulled into orbit, forming an acretion disk. The acretion disk has a whole lot of friction due to the fact that so many particles are rubbing against each other as they swirl around the black hole at colossally high speeds. Temperatures, electric fields, and magnetic fields in these kinds of environments get vey chaotic and hot. So hot in fact, that the disk surrounding the black hole begins to glow with energetic X-ray light.
    In other cases, like the average density of the whole universe, that comes into a factor of about five hydrogen atoms per cubic meter, or approximately 9.47 x 10(-27) kilograms/ m^3
    To get an even better idea, imagine a cubic yard of empty space, then put only 5 protons in that cubic yard. That is the critical density of our universe.
  5. Nov 24, 2014 #4
    Well... Air Drag is given by ##(0.5).C.d.v^2##
    Where d I density...since density of gas in space I very low, air drag is negligible.
  6. Nov 24, 2014 #5


    User Avatar

    Even at very low densities, air friction -drag- does exists. For example, if at ground level, with an air density of 1280 kg/m3, a moving object has a drag of 100 newtons at a velocity of 10 m/s

    But with a diminishing density, drag may be kept constant by rising the speed. If we fly so high that the density is 1/10000 of that at sea level, we can keep the drag (and the lift) constant if we compensate by rising the speed by a factor of 100...
  7. Nov 24, 2014 #6


    User Avatar
    Science Advisor
    Gold Member

    This is true, but space is way way emptier than 1/10000 the atmosphere at sea level. The actual density of particles in space is something like 1 particle per cubic meter or something like that...IIRC (but I think this is for the intergalactic medium, the ISM might be a little bit denser). So something like 26 or more orders of magnitude thinner than the air we breathe. So, to get some appreciable drag, you have to be traveling quite close to the speed of light I think...and at those velocities, I'm not sure how to calculate the drag correctly.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook