Friction in a vacuum?

Discussion in 'Physics' started by tjohnson, Jan 29, 2015.

  1. Papabravo

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    Feb 24, 2006
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    Friction depends on the normal force and the surface properties of two materials. There is no dependence on ambient pressure or lack thereof. Did your degree come from the University of Kingman Reef?

    https://en.wikipedia.org/wiki/Kingman_Reef
     
  2. MrAl

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    Jun 17, 2014
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    Hi,

    This has probably been mentioned before, but are you talking about the resistance due to air near the surface of the earth vs that in free space where there is no air?

    Air resistance is due to the density of air and something moving through it experiences the molecules in the air.

    Sliding friction on the other hand depends on the surface roughness which has much less to do with the air because the surface friction will usually be much more than the air resistance. If the sliding friction was low, then the air might have a significant effect, but we usually aim to separate the two functions so we can understand them independently of each other, then add the two when needed.

    Since a vacuum is less dense than air, there would be less friction. We then get into the question of is there such a thing as a perfect vacuum.
     
  3. nsaspook

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    Last edited: Apr 11, 2017
  4. Sitara

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  5. wayneh

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    The quality of answers here greatly exceeds the quality of the question.

    That's harsh. I went back and re-read the original question and it's fine.

    My opinion is that drag due to motion through fields is not friction. To my mind, friction requires matter moving against matter. Perfect vacuum would have zero 'air' friction.
     
    Last edited: Apr 13, 2017
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  6. BillO

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    Nov 24, 2008
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    When 'matter' moves against 'matter' the interaction is all in the fields produced by the particles of which the matter is composed. Specifically, friction is due to the interaction of EM fields created by the particles in the matter.

    The OP's question arose from an article to which he gave a link. The friction discussed there is friction associated with 'virtual' photons. Virtual photons, according to QM, are constantly created and destroyed in otherwise empty space. They do not exist for very long, but even a short interaction between them and some matter possessing mechanical energy of some kind would presumably turn them form 'virtual' photons to real photons and in doing so extract a tiny amount of the mechanical energy from the matter.

    A true vacuum can only exist in theory and will never be achievable. The reason I say this is that if one were obtained, it would cease to be observable simply due to the fact that there would be no exchange particles (photons, or any other kind) coming from it to be observed.
     
  7. nsaspook

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    Virtual photons and friction? Oh god! https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
     
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  8. BillO

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    Well,

    I'm not going to say who guess is right, Alejandro Manjavacas and F. Javier García de Abajo's or Arnold Neumaier's. They are both expressing as of yet untested notions. I was just summarizing the hypothesis presented by the Spaniards that lead to the OP's question. However, I'll keep an open mind about it until we have a resolution of the question one way or the other. Like I did for the HIggs boson and cold fusion. One of those proved to exist, the other did not.
     
  9. nsaspook

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    I think it helps to actually understand what is a “virtual particle” before we start giving it properties that are unlikely to exist for it.
    https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/
     
  10. BillO

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    I'm not in argument with you on this nsaspook. What Strassler presents here is a layman's explanation of a virtual particle, and I don't really have an issue with it. I think what the Spaniards were imagining was that if one of these 'disturbances' coincides with the opportunity to extract mechanical energy from a mass that perhaps a real particle (or a real particle pair) will be produced. The resulting particle(s) will then travel off through space taking their stolen energy with them. Energy they stole from the mass leaving it with a bit less.

    Again, I want to stress that I'm not proponent of their musings, nor am I a proponent of Neumaier or Strassler. What I am a proponent of is everyone and anyone using their noggins to come up with considered notions. None of this has been tested, but it is all interesting thought and, prima facie, plausible.
     
  11. nsaspook

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    I understand but the basic problem is 'virtual' particles only add a BS factor to the understanding of how this might be happening. There is zero evidence of it being a actual scientifically proven process of energy transfer using virtual photons from random vacuum fluctuations. Neumaier or Strassler and most actual experts imply most of what that newscientist article says is a simplistic myth and a confusing misstating of the process that might account for a possible energy transfer if its ever seen by a future experiment..

    The actual scientific paper sticks to proper science without the 'virtual' photon crap.
    https://arxiv.org/pdf/1009.4107.pdf
     
    Last edited: May 16, 2017
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