science

Lubricant

Lubricant is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lubricant rather than just read about it. In short: A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces.

Key takeaways

Lubricant belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lubricant to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lubricant from memory before moving on to harder problems.

Reference excerpt

A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. A lubricant's effectiveness against friction is measured as its lubricity and the study of lubrication in material science is known as tribology. In addition to industrial applications, lubricants are used for many other purposes. Other uses include cooking (oils and fats in use in frying pans and baking to prevent food sticking), to reduce rusting and friction in machinery (through the use of motor oil and grease), and bioapplications on humans (e.g., lubricants for artificial joints, ultrasound examination, medical examination, and sexual intercourse). It is mainly used to reduce friction and to contribute to a better, more efficient functioning of a mechanism.

History Lubricants have been in some use for thousands of years. Calcium soaps have been identified on the axles of chariots dated to 1400 BC. Building stones were slid on oil-impregnated lumber during the construction of the Egyptian pyramids. In the Roman era, lubricants were based on olive oil and rapeseed oil, as well as animal fats. The development of lubrication accelerated in the Industrial Revolution to match the rise of metal-based machinery. Whale oil was a historically important lubricant, with some uses up to the latter part of the 20th century as a friction modifier additive for automatic transmission fluid. Relying initially on natural oils, needs for such machinery shifted toward petroleum-based materials early in the 1900s. A breakthrough came with the development of vacuum distillation of petroleum, as described by the Vacuum Oil Company. This technology allowed the purification of very non-volatile substances, which are common in many lubricants. In 1999, an estimated 37,300,000 tons of lubricants were consumed worldwide. Automotive applications dominate, including electric vehicles but other industrial, marine, and metal working applications are also big consumers of lubricants. Although air and other gas-based lubricants are known (e.g., in fluid bearings), liquid lubricants dominate the market, followed by solid lubricants.

Liquid lubricants Most lubricants are composed of a majority of "Base oil", often a viscous liquid hydrocarbon, plus a variety of additives. Many lubricants contain no additives, e.g. compressor and hydraulic oils. On the other hand, greases, metalworking fluids, and gear lubricants can contain up to 30% additives by weight.

Base oil The base oil is the main component of all liquid lubricants. Two main types of base oils are mineral oil and synthetic oils

Mineral oil The term "mineral oil" is used to refer to lubricating base oils derived from crude oil. The American Petroleum Institute (API) designates several types of lubricant base oil:

Group I – Saturates < 90% and/or sulfur > 0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120 Manufactured by solvent extraction, solvent or catalytic dewaxing, and hydro-finishing processes. Common Group I base oil are 150SN (solvent neutral), 500SN, and 150BS (brightstock) Group II – Saturates > 90% and sulfur < 0.03%, and SAE viscosity index of 80 to 120 Manufactured by hydrocracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color. Group III – Saturates > 90%, sulfur < 0.03%, and SAE viscosity index over 120 Manufactured by special processes such as isohydromerization. Can be manufactured from base oil or slax wax from dewaxing process. Group IV – Polyalphaolefins (PAO) Group V – All others not included above, such as naphthenics, polyalkylene glycols (PAG), and polyesters. The lubricant industry commonly extends this group terminology to include:

Group I+ with a viscosity index of 103–108 Group II+ with a viscosity index of 113–119 Group III+ with a viscosity index of at least 140 Can also be classified into three categories depending on the prevailing compositions: paraffinic, naphthenic, and aromatic.

Synthetic oils Petroleum-derived lubricant can also be produced using synthetic hydrocarbons (derived ultimately from petroleum), "synthetic oils". These include:

Polyalpha-olefin (PAO) Synthetic esters Polyalkylene glycols (PAG) Phosphate esters Perfluoropolyether (PFPE) Alkylated naphthalenes (AN) Silicate esters Ionic fluids Multiply alkylated cyclopentanes (MAC)

Additives

A large number of additives are used to impart performance characteristics to the lubricants. Modern automotive lubricants contain as many as ten additives, comprising up to 20% of the lubricant, the main families of additives are:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Lubricant

Start with the simplest possible case. Write down what Lubricant claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lubricant before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lubricant ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lubricant

In research: Lubricant appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lubricant in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lubricant is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lubricants, Petroleum products, Tribology, so understanding it makes those chapters shorter.
In everyday life: Look for Lubricant outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lubricant in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lubricant means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lubricant out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lubricant in simple terms?

Why does Lubricant matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lubricant?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lubricant.