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Friction at the atomic scale. From the article "Friction at the Atomic Scale" by Jacqueline Krim we learn that standard friction and friction at the atomic scale are quite different. In my summary paper I would like to try to explain that fact based on the article. Having used different apparatus, the scientists made an experiment to prove that physicists didnt pay enough attention to the study of frictions atomic level or nano tribology for a long time wrongly. However now it was determined that the force originates from different surprising sources, including sound energy.
For there experiment scientists used the following apparatus: Quartz-crystal microbalance that can make the measurements of friction between its electrode and a cover of substance with small thickness put on the electrode. Alternating of the vibration parameters of the quartz show how much the put layer slips on the object lying under it. The artful simulations of the sliding layers made on the computer, such liquid krypton are applied to prove the results. The next apparatus is Surface-forces apparatus that apply two cleaved mica surfaces. These surfaces are applied because they are the smoothest. Researcher can put lubricant lamina, the thickness of which can be just two molecules, between the mica surfaces and slide them in order to see how the lamina influence the sliding.
The next apparatus used is Lateral-Force Microscope. It is a sort of the atomic-force microscope. It uses a small needle fixed on a cantilever with its tip on the sample object. The light is reflecting off the tip shows the degree of deflection that means that it shows a measure of the friction between the tip and the surface.
Investigator used the microscope to pull islands of carbon 60 across a salt surface. Friction is more difficult than the standard explanation suggests. Scientists still try to understand what really originate friction. Actually the first testing on that question was made by Leonardo da Vinci.
The friction may drop off with coarseness and in the other case in cold welding very flat surface may have colossal friction. This disproves standard description because according to the result of the experiments friction is defined by the contact area of the two things. The contact area is a place where the one object touches the other, and not the evident place of contact. It is the area of all the infinitesimal place of contact of the two of them.
The Friction depends on the contact area size. If the contact area is large, the friction is higher and vice versa. This is perfectly explained by the special model called the model of molecular cohesion. It is showing the friction as the solidarity of molecules of the testing objects. The molecules of one surface need to come very close to the molecules of the other object for the interaction.
These contact places should create some kind of wear. This model was explained in the wrong way when in the 1970 's Jacob Israelashvili presented obvious proof for a wear-free friction. The present model explaining wear-free friction was built on the basis of the atomic lattices vibrations. The main idea was that friction appears when atoms of the one substance are moving because of sliding of the other surface atoms. These oscillations are defined by the term phonon.
They are actually sound waves which ultimately became heat. The amount of the mechanical energy (the energy that is necessary to provide the movement of the object) becoming phonons is defined by the features of the sliding surface because various substances oscillate a definite special frequencies. If one surface has many identical frequencies with another substance friction will be higher. Microscopy of friction force under ultrahigh vacuum conditions appears to be a perfect method to examine miniature contacts. Atomic scale slipping is investigated with the help of the experiment made under ultrahigh vacuum conditions. The loading and velocity dependence are investigated with keen probing elements on objects, such as KBr (001) and Cu (111).
The velocity contingent atomic friction is studied according to thermal activation. Microscopic strictures, such as the substance potential barrier height and the test frequency of that atomic contact, become known during this testing. For undersized used normal forces, a changing of atomic-stick slip to the sliding with smallest squandering is noticed. Now we see that friction is more difficult than the standard explanation suggests. I would like to show the difference between the standard explanation of friction and friction at the atomic scale. In order to do that I will use the properties of standard friction given by Getty's, Keller, and Skove in Classical and Modern Physics and the properties given by Jacqueline Krim in her article "Friction at the Atomic Scale." Getty's, Keller, and Skove, Classical and Modern Physics, McGraw-Hill, Inc, (1989) p. 106.
The friction force that resists sliding is proportional to the normal load (or the force that squeezes the surfaces together). This proportionality constant is usually referred to as the friction coefficient. The amount of friction is independent of the area of contact (for a wide range of areas). The friction force is independent of sliding speed (once the sliding starts). Scientific American, October 1996, "Friction at the Atomic Scale" by Jacqueline Krim, pp. 48 - 56.
The friction force depends on how easily to surfaces become stuck relative to becoming unstuck: it is proportional to the degree of irreversibility of the force that squeezes the two surfaces together, rather than the outright strength of the force. This is called the adhesion hysteresis, which differs from adhesion. The friction force is directly proportional to the ACTUAL, rather than the apparent, area of contact. The friction force is directly proportional to the sliding speed of the interface at the true contact points, as long as the surfaces do not heat up and are sliding at speeds below the speed of sound. Bibliography: Getty's, Keller, and Skove, Classical and Modern Physics, McGraw-Hill, Inc, (1989) p. 106. Scientific American, October 1996, "Friction at the Atomic Scale" by Jacqueline Krim, pp. 48 - 56.
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Research essay sample on Friction At The Atomic Scale
