What Is Friction?
Friction is the contact force between two surfaces that opposes (or opposes the tendency of) relative sliding. Two regimes:
Static friction, Fs ≤ μs N, prevents sliding from starting. The actual value adjusts to whatever is needed up to the maximum μs N.
Kinetic (sliding) friction, Fk = μk N, acts while surfaces slide. Almost always μk < μs. The coefficients depend on both surfaces (rubber on dry asphalt μs ≈ 0.9; steel on ice μk ≈ 0.03) but only weakly on the apparent contact area.
Microscopically, friction arises from adhesion at asperity contacts and from plastic deformation. Kinetic friction converts mechanical energy into heat (and to a small extent sound and wear).
Recent research on this topic from arXiv
Preprints and papers indexed on arXiv.org. Links open the public abstract pages.
- Sliding with Friction and The Brachistochrone Problem
Alexander Kurilin · 2025 ·arXiv:2501.18622v1
We analyze the motion of a particle in the gravity field along a family of differentiable curves taking into account the Coulomb friction forces. A parametric equation of the optimal curves is given that generalizes the cycloid one in this... - A Pedagogical Model of Static Friction
Galen T. Pickett · 2015 ·arXiv:1507.04015v1
While dry Coulombic friction is an elementary topic in any standard introductory course in mechanics, the critical distinction between the kinetic and static friction forces is something that is both hard to teach and to learn. In this pape... - Granular Brownian motion with dry friction
A. Gnoli, A. Puglisi, H. Touchette · 2013 ·arXiv:1303.5241v2
The interplay between Coulomb friction and random excitations is studied experimentally by means of a rotating probe in contact with a stationary granular gas. The granular material is independently fluidized by a vertical shaker, acting as... - Large scale inhomogeneity and local dynamical friction
A. Just, J. Penarrubia · 2004 ·arXiv:0410740v1
We investigate the effect of a density gradient on Chandrasekhar's dynamical friction formula based on the method of 2-body encounters in the local approximation. We apply these generalizations to the orbit evolution of satellite galaxies i...