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If according to physics, we cannot touch anything and the sensation appears only due to a repulsive force between the atoms, then how does friction occur?

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  • $\begingroup$ Possible duplicate of How is frictional force dependent on normal reaction? $\endgroup$ – John Rennie Jan 5 '18 at 17:35
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    $\begingroup$ @JohnRennie The question your link guides to is considering friction in the macro world. I asked about friction in the micro world. $\endgroup$ – user160598 Jan 5 '18 at 18:01
  • $\begingroup$ @user160598 redefining the interaction by stating that there is no contact at the micro level does not change the mechanism, and cannot possibly alter our understanding of the process. Given that our understanding is built upon that same system—of subatomic interactions—redefining the process will only lead to the same ultimate understanding through a different means of measurement. $\endgroup$ – Kieran Moynihan Jan 5 '18 at 18:41
  • $\begingroup$ In truth, the only things we can touch, are those which exert a repulsive force of some sort! Even two attractive magnets, are only deemed to be touching once they move so close as to repel each other. Two water droplets that attract each other only touch in the moment when their surface tension repels - if it is overcome, they cease to be touching and instead become a single undifferentiable unit. $\endgroup$ – Steve Jan 6 '18 at 20:55
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The most fundamental explanation - the electromagnetic force. Atoms trying to push against other atoms. And either the push or pull is deflected or shears off atoms molecules or groups of molecules leading to energy loss, through a greater degree of'jiggling' of the atoms in the vicinity of the frictional interface (increase in temperature). And so then this energy eventually lost to radiation or conduction.

Engineers and I suppose physicists also categorize friction as static or dynamic according to whether the object or system experiences friction in a non-moving or moving state respectively. In static friction the two members are locked in equilibrium, the applied force being countered by opposition forces at the atomic level. This state can only exist up to a threshold of applied force after which motion happens and you have dynamic friction.

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  • $\begingroup$ What happens in a dynamic friction? What happens there? $\endgroup$ – user160598 Jan 5 '18 at 18:07
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    $\begingroup$ @user160598 "after which motion happens" and all described in first paragraph $\endgroup$ – anna v Jan 5 '18 at 18:34
  • $\begingroup$ dynamic friction often called viscous friction because of the shearing action I suppose. In many physical situations the viscous frictional force can be approximately modeled as linearly proportional to velocity of the interfacing surfaces. In other cases a Coulomb friction model is more appropriate where the force reaches a constant, independent of velocity. And there's stiction ... but that models the static friction. Google, and read! $\endgroup$ – docscience Jan 5 '18 at 19:56

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