mathematics

Kilometre

Kilometre is a mathematics 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 Kilometre rather than just read about it. In short: The kilometre (SI symbol: km; or ), spelt kilometer in American English, is a unit of length in the International System of Units (SI), equal to one thousand metres (kilo- being the SI prefix for 1000). It is the preferred measurement unit to express distances between geographical places on land in most of the world; notable exceptions are the United States, the United Kingdom, and Liberia where the statute mile is…

Key takeaways

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

Reference excerpt

The kilometre (SI symbol: km; or ), spelt kilometer in American English, is a unit of length in the International System of Units (SI), equal to one thousand metres (kilo- being the SI prefix for 1000). It is the preferred measurement unit to express distances between geographical places on land in most of the world; notable exceptions are the United States, the United Kingdom, and Liberia where the statute mile is used.

Pronunciation

There are two common pronunciations for the word.

The first pronunciation follows a pattern in English whereby SI units are pronounced with the stress on the first syllable (as in kilogram, kilojoule and kilohertz) and the pronunciation of the actual base unit does not change irrespective of the prefix (as in centimetre, millimetre, nanometre and so on). It is generally preferred by the British Broadcasting Corporation (BBC), the Canadian Broadcasting Corporation (CBC), and the Australian Broadcasting Corporation (ABC). Many other users, particularly in countries where SI (the metric system) is not widely used, use the second pronunciation with stress on the second syllable. The second pronunciation follows the stress pattern used for the names of measuring instruments (such as micrometer, barometer, thermometer, tachometer, and speedometer). The contrast is even more obvious in countries that use the American spelling of the word metre. This pronunciation is irregular because it makes the kilometre the only SI unit with the stress on the second syllable. After Australia introduced the metric system in 1970, the first pronunciation was declared official by the government's Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, insisted that the second pronunciation was the correct one because of the Greek origins of the two parts of the word.

Equivalence to other units of length

History

By a decree on 8 May 1790, the French National Constituent Assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the sole length measurement system in the French Republic and it was based on ⁠1/10⁠ millionth of the distance from the orbital poles (either North or South) to the Equator, this being a truly internationally based unit. The first name of the kilometre was "Millaire". Although the metre was formally defined in 1799, the myriametre (10000 metres) was preferred to the "kilometre" for everyday use. The term "myriamètre" appeared a number of times in the text of Develey's book Physique d'Emile: ou, Principes de la science de la nature, (published in 1802), while the term kilometre only appeared in an appendix. French maps published in 1835 had scales showing myriametres and "lieues de Poste" (Postal leagues of about 4288 metres). The Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the mijl. It was only in 1867 that the term "kilometer" became the only official unit of measure in the Netherlands to represent 1000 metres. Two German textbooks dated 1842 and 1848 respectively give a snapshot of the use of the kilometre across Europe: the kilometre was in use in the Netherlands and in Italy, and the myriametre was in use in France. In 1935, the International Committee for Weights and Measures (CIPM) officially abolished the prefix "myria-" and with it the "myriametre", leaving the kilometre as the recognised unit of length for measurements of that magnitude. The symbol km for the kilometre is in lower case and has been standardised by the BIPM. A slang term for the kilometre in the US, UK, and Canadian militaries is klick.

See also Conversion of units, for comparison with other units of length Cubic metre Distance traveled Metric prefix Orders of magnitude (length) Square kilometre

Notes

References

External links

Media related to Distance indicators at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with Kilometre

Start with the simplest possible case. Write down what Kilometre claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, 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 Kilometre 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 Kilometre 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 Kilometre

In research: Kilometre appears in mathematics 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 Kilometre 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: Kilometre is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1000 (number), Metre, Orders of magnitude (length), so understanding it makes those chapters shorter.
In everyday life: Look for Kilometre 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 Kilometre in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kilometre 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 Kilometre out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kilometre in simple terms?

Why does Kilometre matter?

Because it connects several mathematics 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 Kilometre?

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 Kilometre.