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Stick-slip (or "slip-stick") refers to the phenomenon of a spontaneous jerking motion that can occur while two objects are sliding over each other.
Cause
Stick-slip is caused by the surfaces alternating between sticking to each other and sliding over each other, with a corresponding change in the force of friction. Typically, the static friction coefficient between two surfaces is larger than the kinetic friction coefficient. If an applied force is large enough to overcome the static friction, then the reduction of the friction to the kinetic friction can cause a sudden jump in the velocity of the movement.
The attached picture shows symbolically an example of stick-slip.
V is a drive system, R is the elasticity in the system, and M is the load that is lying on the floor and is being pushed horizontally. When the drive system is started, the Spring R is loaded and its pushing force against load M increases until the static friction coefficient between load M and the floor is not able to hold the load anymore. The load starts sliding and the friction coefficient decreases from its static value to its dynamic value. At this moment in fact the spring can give more power and accelerates M. During M’s movement, the force of the spring decreases, until it is insufficient to overcome the dynamic friction. At this point, the M stops. The drive system however continues, and the spring is loaded again etc.
Examples
Examples of stick-slip can be heard from hydraulic cylinders, honing machines etc. Special dopes can be added to the hydraulic fluid or the cooling fluid to overcome or minimize the stick-slip effect. Stick-slip is also experienced in lathes, mill centres, and other machinery where something slides on a slideway. Slideway oil typically lists "prevention of stick-slip" as one of their features. Other examples of the stick-slip phenomenon include the music that comes from a violin, the noise of car brakes and tires, and the noise of a stopping train. Another example of the stick-slip phenomenon occurs when you play musical notes with a glass harp by rubbing a wet finger along the rim of a crystal wine glass. One animal that produces sound using stick-slip friction is the spiny lobster which rubs its antennae over smooth surfaces on its head. 1
Stick-slip can also be observed on the atomic scale using a friction force microscope2. In such case, the phenomenon can be interpreted using the Tomlinson model.
See also: Simulation of stick-slip behaviour in a friction force microscope (movie)
The behaviour of seismically-active faults is also explained using a stick-slip model, with earthquakes being generated during the periods of rapid slip.
References
- ^ S. N. Patek (2001). "Spiny lobsters stick and slip to make sound". Nature 411: 153–154. doi:.
- ^ Atomic-scale friction of a tungsten tip on a graphite surface C.M. Mate, G.M. McClelland, R. Erlandsson, and S. Chiang Phys. Rev. Lett. 59, 1942 (1987)
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- This page was last modified on 6 November 2008, at 04:34.
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