BlogNCERTImportant Topic of Physics: Lubrication

Important Topic of Physics: Lubrication


Friction and lubrication are influenced by parameters such as material properties, surface finish, temperature, sliding velocity, contact pressure, and lubricant characteristics. Each body or object experiences a contact force that always opposes the relative motion between the surfaces whenever the surface of a body slides over another. Such a contact force is known as frictional force. The intermolecular interaction developing due to the elastic properties of matter is the main cause of frictional force. The environment has been applying lubrication since the evolution of synovial fluid, which lubricates the joints and bursae of vertebrate animals.

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    The information about lubrication from various physics-related articles are available here. Lubrication and its type are important topics in physics. Students who want to flourish in physics need to be well known about lubrication to get deep knowledge about it to do well on their exams and it is very much useful in real life. The idea of lubricant, role, and types of lubrication are provided here to assist students in effectively understanding the respective topic. Continue to visit our website for additional physics help.


    Lubrication is a crucial component in the efficiency and life expectancy of any rotating equipment. According to a study by SKF, over 50% of bearing failures are the result of improper lubrication. Selecting the appropriate lubrication solution can help decrease premature bearing failures and increase machine uptime, productivity, and energy efficiency. The lubricant is used to facilitate the relative motion of solid objects. It can be a solid, fluid, or any plastic substance. The lubricants form a film between the metal surfaces of machine parts to avoid metal-to-metal contact and to keep the machine running safely and efficiently. The main objective of lubrication is reducing friction. There are various types of lubrication including boundary lubrication, mixed lubrication, and full film lubrication.


    Lubrication is defined as the technique that is used to reduce friction. The lubricant is a substance that is used to facilitate the relative motion of solid objects by reducing friction and wear between interacting surfaces.

    Various substances are used to lubricate a surface. Oil and grease are the most common examples of lubricants. Grease is made up of oil and a thickening agent to attain its consistency, but the oil is what actually lubricates. Whereas oils can be synthetic, vegetable or mineral-based as well as a combination of these. The application defines which particular oil, commonly referred to as the base oil, should be used. But in some conditions, synthetic oils can be beneficial.

    The lubricants consisting of oil may have some additives which increase, add or suppress properties within the base oil. The quantity of such additive substances depends on the type of oil and the application for which it is being used. For example, a dispersant is added to the engine oil.

    The dispersant keeps the matter that is insoluble together to be removed by the filter upon circulation. In some environments that undergo extremes in temperature, a viscosity index (VI) improver may be added. Such additives are very long organic molecules that stay bunched together in cold conditions and unravel in hotter conditions. This procedure changes the oil’s viscosity and lets it flow better in cold conditions while still maintaining its high-temperature properties. The one and only problem with addictive substances is that they can be depleted, and in order to retain them back to sufficient levels, generally the oil volume must be replaced.

    The Role of a Lubricant:

    The basic functions of a lubricant are:

    • Reduce friction
    • Prevent wear
    • Protect the equipment from corrosion
    • Control temperature (dissipate heat)
    • Control dilution
    • Transmit power (hydraulics)
    • Provide a fluid seal

    Sometimes the objectives of decreasing friction and avoiding wear are used interchangeably. Generally, friction is the resistance to motion, and wear is said to be the loss of material as a result of friction, contact fatigue, and corrosion.

    Decreasing friction is a key function of lubrication, but there are many other benefits of this process. The lubricating films can be used to prevent corrosion by protecting the surface from water and other corrosive materials. Also, they play an important role in limiting contamination within systems.

    The lubricant acts as a channel in which it transfers contaminants to filters to be removed. These liquids also aid in temperature control by soaking up heat from surfaces and transferring it to a point of lower temperature where it can be dissipated.

    Types of Lubrication:

    There are 3 various types of lubrication: boundary, mixed and full film. Each type is different, but they all rely on a lubricant and the additive substances within the oils to protect against wear.

    (1) Full-film lubrication:

    The condition in which the load-carrying surfaces are separated by a relatively thick film of lubricant. It can be broken down into two forms: hydrodynamic and elastohydrodynamic.

    Hydrodynamic lubrication takes place when two surfaces in sliding are fully differentiated by a film of fluid. Elastohydrodynamic lubrication is somewhat similar but happens when the surfaces are in a rolling motion. The film layer in elastohydrodynamic conditions is thinner than that of hydrodynamic lubrication, and the pressure on the film is comparatively greater. This type of lubrication is called elastohydrodynamic because the film elastically deforms the rolling surface to lubricate it.

    Sometimes, on the most polished and smooth surfaces, irregularities may present. They will stick out of the surface forming peaks and valleys at a microscopic level. Such peaks are called asperities. For full-film conditions to be met, the lubricating film should be thicker than the length of the asperities. This kind of lubrication saves surfaces the most effective and is the most desired.

    (2) Boundary lubrication:

    It can be seen where there are frequent starts and stops, and where shock-loading conditions are present. Some of the oils have extreme-pressure (EP) or anti-wear (AW) additives to protect surfaces in the event that full films cannot be achieved due to speed, load, or other factors.

    These additives hold on to metal surfaces and form a sacrificial layer that saves the metal from wear. The boundary lubrication happens when the two surfaces are contacting in such a way that only the EP or AW layer is all that is protecting them. This type is not ideal, as it results in high friction, heat, and other undesirable effects.

    (3) Mixed lubrication:

    It is a cross between boundary and hydrodynamic lubrication. When the bulk of the surfaces is differentiated by a lubricating layer, the asperities still make contact with each other. This is where the additive substances again come into play.

    Having a better understanding of this process, it must be easier to determine what lubrication actually is. This is a process of either separating surfaces or saving them in a manner to decrease friction, heat, wear, and energy consumption. It can be achieved by using oils, greases, gases, or other fluids.

    Also read: Work Done by a Constant Force

    Frequently Asked Question (FAQs):

    Question 1: What do you mean by the viscosity index of edible oil?

    Answer: The viscosity index available for lubricant oil explains the quality of that particular lubricant oil. So, the viscosity index of edible oil is related to the quality of edible oil.

    Question 2: Can two lubricants be mixed together in the same engine?

    Answer: It is not recommended, but if for some reason different oils must be mixed, it is important to follow certain recommendations. It is better to use an oil with the same level of quality as the one that is currently being used in the vehicle and, if possible, from the same manufacturer. In addition, during the next oil change, it is a good idea to replace the oil filter with a new one.

    Question 3: Can a lubricant reduce fuel consumption?

    Answer: Modern lubricants should be put through trials to certify that they lower fuel consumption or certain properties inherent to that feature are required. Some manufacturers’ specifications highlight the fuel-saving properties of the product, which are usually used to promote it.

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