Friction is electricmagnetic force; why friction is not conserved?

[Haorong Wu]

Obviously, friction is not a result of other three kinds of force, and electricmagnetic force is conserved, then why friction is not conserved?

 

[Dale]

Energy is always conserved, so that is not relevant. For a force to be conservative it must satisfy $\oint \vec F \cdot d\vec r = 0$ which friction does not.

 

[nasu]

Forces may be conservative (or not). There is no such thing as "conservation of forces".

If you look at a microscopical picture, indeed most of the macroscopic forces (not just friction) are the result of electromagnetic interactions. But then you have to be consistent with the microscopic view. The result of friction is the increase in the kinetic energy of some molecules but this increase does not result in an increase of the KE of the macroscopic bodies.
So as Dale said, the energy is conserved.
The mechanical, macroscopic energy is not.

 

[gmax137]

If you are sitting at the breakfast table and gently push your bowl away from you, you can "feel" the friction, right -- you have to "push"? Now when you pull the bowl back closer to you do you feel the same, or does the bowl seem to be pushing your hands along?

Now compare that to say, picking up a suitcase. You pull on up the handle, the suitcase rises up from the floor. When you let it back down, you feel it pulling down? Or do you have to push it back down?

 

[jtbell]

Friction is electricmagnetic force; why friction is not conserved?

Did you mean to say "why friction is not a conservative force"?

The electromagnetic force in general is also not conservative.

The electrostatic force (Coulomb's law) is indeed conservative, and you can define a potential energy for it. However, the "electrodynamic" force (e.g. in Faraday's law) is not conservative, neither is the magnetic force in general.