also known as sonic lubrication occurs when sound
(measurable in a vacuum by placing a microphone on one element of the
sliding system) permits vibration to introduce separation between the
sliding faces. This could happen between two plates or between a series of
particles. The frequency of sound required to induce optimal vibration, and
thus cause sonic lubrication, varies with the size of the particles (high
frequencies will have the desired, or undesired, effect on sand and lower
frequencies will have this effect on boulders).
If there is a dynamic
coefficient of friction between two objects of 0.20, and vibration
causes them to be in contact only half of the time, that would be equivalent
to a constant coefficient of friction of 0.10. This substantial reduction in
friction can have a profound effect on the system.