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Which materials have the highest coefficients of friction?

  1. Apr 3, 2017 #1
    I am aware that there needs to be two materials for there to be a coefficient of friction, but I mean in general. For example, I know synthetic setae are very resistant to slipping on surfaces.
     
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  3. Apr 3, 2017 #2

    phinds

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    Low grit sandpaper is really good at not slipping over wood :smile:
     
  4. Apr 4, 2017 #3

    CWatters

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  5. Apr 4, 2017 #4

    JBA

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    Depending upon your application, non-skid tape sold for boat and running board applications is quite good for both wood and other mating soft materials and for ice as well; but, it wears out quickly against concrete.
     
  6. Apr 4, 2017 #5

    Baluncore

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    The highest coefficients of static friction are for dry contact between identical metals.
    Examples of coefficients ≥ 1.00 are;
    1.00 Iron — self
    1.00 Copper — self
    1.05 Copper — Cast iron
    1.10 Cast iron — self
    1.10 to 1.35 Aluminium — self
    1.15 Rubber — self
    1.20 Platinum — self
    1.40 Silver — self
    1.46 Indium — self
     
  7. Apr 5, 2017 #6
    That's interesting I did not know that about self stick of metals
     
  8. Apr 6, 2017 #7

    Baluncore

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    The setae on small animals feet conform to follow the surface so a high proportion of the area can have an attractive adhesion. By conforming to the surface there is never a high pressure exerted on a high point that would push the foot away from the surface and counter the adhesion.

    The friction coefficient is I believe a different phenomenon. With friction, only the total force is important because some patches will carry higher contact force while others patches will have none. Friction is one sided. It does not allow you to walk across the ceiling, or even to climb a vertical wall.

    Yes, it is peculiar since the dry surfaces do not immediately cold weld to each other. Maybe there is enough surface oxidation to prevent a weld forming.

    The crystal structure in the two samples is extremely unlikely to be aligned on the sample interface so the contact surface must be the average of all the diagonal contact “dislocations”, hence the high coefficient without a weld forming.

    The thing that at first glance surprised me was indium. It has the highest static coefficient against itself in the list, yet it is used as the surface layer on thin shell engine bearings. I believe that is because it is highly resistant to acids and runs only against cast iron, steel or chrome that is very well lubricated with oil.

    The list also demonstrates another reason why copper sheet makes such a good head gasket for old tractors with cast iron blocks and heads.
     
  9. Apr 6, 2017 #8

    jack action

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    I once asked a tire company about drag tire friction coefficient. Here what was their response:
     
  10. Apr 6, 2017 #9
    This is pure speculation but maybe the similarities of field allow the two samples to get closer together ... The only way I can think to say it is, less zero distance?
     
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