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Friction Measurement, Its Importance and Use of a Tribometer

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Friction is an every day occurrence and has a lot of importance. It can be measured by a Tribometer

Before we measure Friction it is important to understand what Friction is. Friction is a force that is generated, when two surfaces are in contact with each other. An example is a motor tire in contact with a road surface. When the tire moves relative to the road it generates a force which is referred to as friction. This force is a general force and is all-pervading and will emanate from the relative motion of solid surfaces, fluids and any material that can move against another commodity or material. It flows directly from Newton’s laws of motion and their reference to force.

A layman can understand Friction as slipperiness. This quality of relative motion between two medium and surfaces results in friction. As a corollary when these surfaces move heat is generated. An example is when two Flintstones are rubbed to generate a spark and fire. This also generates heat. Along with the generation of heat another side effect of friction is wear and tear. Thus a motor tire when in constant use over a road surface is apt to suffer wear and tear and suffers degradation.

Keeping the above in mind a measurement of this force .i.e. Friction has importance in everyday life and also for science. The measurement of this force is done by a tribometer. This is an instrument that measures Friction on a surface. We must understand that this measurement of Friction refers to a number of types of friction like dry friction ( solids), fluid friction( liquids), lubricated friction( Fluid related to solids), skin friction( solid body through a fluid) and internal friction.

Another question that we must ask is as to what are we measuring? What is the unit for it? In this the tribometer will measure something called the ‘coefficient of friction' (COF). In scientific parlance it is represented by the symbol µ. The coefficient of friction depends on the materials used; for example, two greased surfaces will have a low coefficient of friction, while rubber on a tarred road will have a high coefficient of friction. Coefficients of friction range from near zero to greater than one. Thus it is not possible to have zero coefficient of friction as that will mean there is no motion and not as such possible. A tire on concrete may have a coefficient of friction of 1.7.

The coefficient of friction is an empirical measurement – it has to be measured experimentally. The principle is that rougher surfaces will have higher effective values than smoother surfaces.

As already brought out the tribometer is the instrument that measures the coefficient of friction, friction force, and wear volume, between two surfaces in contact with each other. It was invented by the 18th century Dutch scientist Musschenbroek.

A simple example of a tribometer is to have two masses in contact with each other with a string and moving one of the masses relative to the other mass. The coefficient of friction, µ, when the system is stationary, can be found out while moving one of the masses relative to the other mass. Then using the general equation for friction force:

N= µ F  

Where N, the normal force, is equal to the weight (mass x gravity) of the sitting mass (mT) and F, the loading force, the coefficient of friction can be worked out.

The science of friction and its measurement is important and the field is fascinating as a study for scientists and Physicists.

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Madan G Singh

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