Boundary friction occurs when a surface is at least partially wet, but not so lubricated that there is no direct friction between two surfaces.
The Effect
When two consistent, unlubricated surfaces slide against each other, there is a specific, predictable amount of friction that occurs. This amount increases as velocity does, but only up to a certain point. That increase generally follows what is known as a
Stribeck curve, after
Richard Stribeck Richard Stribeck (7. July 1861 in Stuttgart , † 29. March 1950) was a German engineer, after whom the Stribeck Curve is named.
Life
Stribeck studied mechanical engineering in 1880 at the Technical University of Stuttgart in 1885 and worked as a ...
. On the other hand, if the two surfaces are completely lubricated, there is no direct friction or rubbing at all. In real life, though, there is often a situation where the surfaces are not completely dry, but also not so lubricated that they do not touch.
This "boundary friction" produces various effects, like an increase in lubrication through the generation of
shearing force
In solid mechanics, shearing forces are unaligned forces acting on one part of a body in a specific direction, and another part of the body in the opposite direction. When the forces are collinear (aligned with each other), they are called ...
s, or an oscillation effect during motion, as the friction increases and decreases.
Kinetic Boundary Friction
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For example, one can experience vibration when trying to brake on a partially damp road, or a cold glass that is slowly condensing moisture can be lifted until it spontaneously slides across the surface it is resting on.
References
Friction
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