Definition

Acoustic/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).

Examples

If there is a dynamic coefficient of friction between two object 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. World War II Panzer tank treads lubricated by their own squeak provide the most famous, if serendipitous, example. This article is about the resistive force. ... PzKpfw V-D, a Panther tank   Panzer? is German for armour. ... Serendipity is finding something unexpected and useful while searching for something else entirely. ...

Another example occurs during landslides. Most landslides do not involve this effect, but occasionally the frequency of vibrations caused by the landslide is optimal to cause the boulders to vibrate. In this case, feedback causes the boulders to slide much faster and quicker than typical, which can pose an increased danger to those in their path. One notable feature of such a landslide is that it appears to be flowing water, or mud, not sliding rocks.

Applications

Besides the study of landslides, there could be many other applications for acoustic lubrication, particularly where variable friction is required or traditional lubricants can't be used. One case might be drilling wells (for water, oil, etc.) through sand. The proper frequency sound could reduce the friction between the drill and sand considerably.

See also

• Friction