# At a microscopic level, how does friction come into exist? [duplicate]

The simplest answer is that the protuberances on the rough surfaces have inelastic collisions on each other and thus have a macroscopic tendency to impede motion.

Is there any more comprehensive and complete theory about how friction rises?

Is f=μN a theoretical conclusion or an approximate experimental result?

Why is the magnitude of friction LINEARLY proportional to the normal force exerted on the contact surface?

## marked as duplicate by John Rennie, valerio, Jon Custer, Chris♦, sammy gerbilFeb 5 '18 at 14:54

• Ultimately it's all about electrodynamics. – Rexcirus Feb 4 '18 at 15:46
• $F=\mu N$ is purely empirical. – valerio Feb 4 '18 at 15:54
• if you google "microscopic view of friction" a number of references come up – anna v Feb 4 '18 at 17:57