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Homework Help: Intermolecular bonds and static friction

  1. Feb 27, 2006 #1
    Hey there,
    I'm trying to find some information on static friction, particularly extended theories of Amonton's. So far, I've found that Amonton said that static friction is a result of surfaces conforming to each other while not moving. I'm tyring to find recent extensions to this theory, mainly like this: "On the molecular level, it has been extended lately to propose that the intermolecular forces have time to make tiny bonds between molecules of the object with molecules of the surface. These extra forces have to be overcome to start the object moving, causing the static friction to be higher than the kinetic friction." I've done searches on Google, but I can't seem to come up with anything. I find lots of information about the surfaces conforming with each other, but nothing on bonds formed on stationary objects.


    Edit: By doing further research I am guessing that the bond that forms between the object and the surface would be classified as Dipole-Dipole since this is a relatively weak force but involves neutral molecules?

    Last edited: Feb 27, 2006
  2. jcsd
  3. Feb 27, 2006 #2

    Andrew Mason

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    Most of the friction (static or kinetic) is the result of mechanical contact between two slightly rough surfaces. Little pieces of matter in one surface (ie fixed to one surface by molecular bonds) are mechanically displaced by the motion of the other surface. So the force of friction is used to break those molecular bonds.

    There is another, much weaker aspect involving molecular bonds. Think of a rolling tire made of soft rubber on an asphalt surface on a hot day. The rubber is mildly 'sticky' and so is the road. So some hydrogen bonds are formed between the rubber and the tar surface of the road. As the tire rolls, these bonds are continually made and broken. This contributes to the coefficient of 'rolling friction'.

    I suspect that there are always some of these bonds forming between any surfaces in contact.

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