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cause of friction is said to be electromagnetic forces between the surfaces of solids in contact. it is defined to be the horizontal component of the contact force. this implies that friction acts on a body at rest also; which is strange? if such interparticle electromagnetic forces are responsible for friction why is it independent of surface area of contact? for surfaces of given materials, friction is more in case the surfaces are smooth or rough? can the value of coefficent of friction (static or dynamic) be greater than 1?

10 years ago

Answers : (1)

Askiitians Expert Bharath-IITD
23 Points

Dear Raghav,

               As u explained the friction is due to electromagnetic forces forces but these are only interactions and they will be in equilibrium. Now when we try to move the object this equilibrium is lost. Thus an oppositie foce known to be frictional force is developed to regain the equilibrium.

But these forces depends only on the nature of the materials in contact but not the area(the force we experience is not the net effect of the electromagnetic interactions). The statement given below is Amontons' 2nd Law

"The force of friction is independent of the apparent area of contact". (Amontons' 2nd Law) (Amontons' 2nd Law does not work for elastic, deformable materials. For example, wider tires on cars provide more traction than narrow tires for a given vehicle mass because of surface deformation of the tire)

Friction is more in the case of rough materials because of both electromagnetic interactions and the interlocking of the surfaces in contact (but not due to the increase of surface area).

Yes it can be greater than 1 in case of nail pinned into a wall, while walking or driving on sand, etc.


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Adapa Bharath

10 years ago
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