| MadSci Network: Physics |
Exciting research is happening in tribology--the science of rubbing surfaces. However, there still is much to learn about what exactly produces it. The simple answer to your question is no--I cannot explain what 'exactly' causes friction. We presently know that there are a number of contributing causes to what we call friction. Some of these are reasonably well understood. For example, real surfaces have some texture. They are not perfectly smooth and flat. For this reason, there can be some geometric components to the frictional force between two surfaces. Particles can get between these surfaces and affect friction. Whether the surfaces are smooth or flat, with or without particles, when one object is pressed against another, there are deformations. These produce energy losses within the deformed materials. All rubbing contacts produce some mechanical deformation friction loss. One source of friction results from these deformations. But these are only part of friction. Adhesion is the second basic source of friction loss. When we get into the details of adhesion, there are many theories, but much is yet to be learned. Electrons from the one surface may interact with those from another. Some think that friction results from vibrations induced by the rubbing. Others believe that quantum effects are involved as atoms of one surface pass close to those of another. We do know that there are electrostatic forces involved in friction. The electron clouds that surround the nucleus of an atom fluctuate randomly. For example, a dense- more negative-part of the cloud will repel the electron cloud on another atom, inducing a positive charge. These will then attract each other. Such forces are known as van der Waals forces. What makes friction here on earth very complex is the fact that all surfaces are contaminated by films, oxide layers, and adsorbed gasses. These alter friction, generally lowering it. For this reason, friction in the vacuum of space tends to be much higher than here on earth. You may find it worth your time to look up the following references on the Internet. The first two are basic, but should be easily understood. http://www.wpi.edu/~nab/atoms.html http://www.wpi.edu/~nab/stroking.html If you wish more information, a good reference on science that includes a section on electrostatic forces is: http://www.triz-journal.com/archives/2000/05/a/ Finally, you wish to tackle an article from New Scientist magazine, vol. 160 no. 2156, p.30(1998) http://fy.chalmers.se/~tfymp/Homepage/friction.html
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