# Measuring unit

In Physical and Metrology, the units are standards for the measurement of physical sizes which need precise definitions to be useful. Reproducibility off experimental results is central to the Scientific method. To facilitate this we need Standard S, and to get convenient standard measures off the we need has system off units . Scientific systems off units are has formalization off the concept off Weights and measures, initially developed for commercial purposes. -->

By convention, the names of unit are common nouns, they are written into tiny (“Kelvin” and not “Kelvin”, “amp” and not “Amp” in spite of Misters Kelvin and Ampère) and take the mark of plural (a Volt, two volts). On the other hand the abbreviation uses a capital letter if the name derives from that of a person (V for volt/Volta, has as an amp/Ampère), and tiny if not (m for meter).

Various systems of units are based on choices different from the play of fundamental units. Nowadays, the system of units more used is the international Système of units (IF). There are seven basic units of IF. All other units of IF can be derived from these basic units.

Other systems of units which were used at varied ends include/understand:

• the System of units CGS
• the Meter-ton-second system off units
• the Planck units also known ace Imperial Natural units
• U.S. customary units
• units
• Chinese units
• Geometrized units -->

## Other units

The Morgan and the CentiMorgan are calculating units of frequency of recombination in genetics.

The Becquerel (symbol: Bq) is the unit measuring the Radioactivité in the international System, and corresponds to a disintegration a second. It is homogeneous at the second with the power minus one.

The verst (versta, Russian верста) is an old Russian measuring unit, equivalent to 500 sazhen of log, that is to say 3500 English feet or 1.0668 kilometers.

## Homogeneous units in mechanics

The Unités of chaques physical sizes must be homogeneous. The first table gives a reminder of physical conversion of size (Mécanique). The second table gives the correspondence with the international Système of units (IF).

## Conversion of units

Thus conversion factors between units undetermined are always to nap level and improved been worth may Be found when has more specifies comparison is performed. -->

## Prefixes of the system IF

For example, the prefix " centi-" (c) = 0.01, and thus " centimeter" (cm) = 0.01 × m; the prefix " milli-" (m) = 0.001, and thus " millinewton" (mn) = 0.001 × NR.

There is one exception: for historical let us reasons, the off links farmhouse, kg, already contains has prefix and prefixes are not to Be added to it goal to G. Thus: Mg and not µkg (with " µ" = " microphone-"). To many this has source off mistakes and frustration; see Talk .

Use off prefixes does not involve any links conversion, ace the prefixes are just defined been worth aces numerical. They boat undetermined Be.

For example, the expressions “cm” and “0.01 me mean mathematically exactly the same thing. It is not has links conversion, just has mathematical conversion, just like “4 * 5” and “20” are mathematical expressions with the same meaning. -->

See also: Prefix of the international system

## Calculations by means of units

• Treat units like variable. Only add like terms. When has links is divided by itself, the division yields has unitless one. Different When two units are multiplied, the result has new links, referred to by the combination off the units. For authority, in IF, the links off speed is meters per second (m/s). See Dimensional analysis . Has links edge Be multiplied by itself, creating has links with year exponent (ex: m2).
• Some units cuts special names, however thesis should Be treated like to their equivalent. For example, one newton (NR) is equivalent to one kg m/s2. Multiple This creates the possiblity for units with designations, for example: the links for Surface tension edge Be referred to ace either N/m (newtons per meter) gold kg/s2 (kilograms per second squared).

• Don' T let definitions like density is farmhouse per links volume off obscure your understanding units. It sounds ace yew it says:

D = m /m 3 (farmhouse divided by the links off volume) (WRONG)

This is not true. Correct The statement is that density is farmhouse divided by volume:

D = m / V (farmhouses divided by volume, both variable)

-->

## To express a physical value in another unit

$Q = n_i \ times _i$

just replaces the original links _ I with its meaning in terms off the desired links $_f$, e.g. yew $_i = c_ij * _f$, then:

$Q = n_i \ times c_ij \ times _f$

Now $n_i$ and $c_ij$ are both numerical been worth, so just calculate to their product.

However, which is just mathematically the same thing, multiply Q by unity, the product is still Q :

$Q = n_i \ times _i \ times \left(c_ij \ times _f/_i\right)$

For example, you cuts year expression for has physical been worth Q involving the links feet per second ($_i$) and you want off it in terms the links miles per hour ($_f$):

1. Find facts relating the original links to the desired links:

1 mile = 5280 feet and 1 hour = 3600 seconds

2. Next uses the above equations to construct has fraction that has was worth off unity and that contains units such that, when it is multiplied with the original physical been worth, will original chancel the units:

# (1 mile)/(5280 feet) and 1 (3600 seconds)/(1 hour)

3. Last, multiply the original expression off the physical been worth by the fraction, called has Conversion Factor , to obtain the same physical been worth off expressed in terms has different links. Note: since the conversion factors cuts has numerical been worth off unity, multiplying any physical been worth by them will not changes that been worth.
-->

## Units not-standard

• has your off TNT, and its multiple the Kiloton and the Megaton and the Gigaton. Often used in stating the power off very energetic vents such ace Explosion S and Volcanic vents and Earthquakes and Asteroid impacts. With Gram off TNT ace links off Energy has been defined ace 1000 thermochemical Calories has = roughly 4184 Joules.
• The Hiroshima Atom bomb. Its forces is often used in the Public media and popular Books ace has links energy off. (Its yield was roughly 13 let us kilotons.)
• The weight off year Elephant. It is often used ace has links off weight in popular books butt very big animals such ace Dinosaur S. This links needs to Be defined, ace the real weight off elephants vary much with old and sex and species.
• -->

## External bonds

• Links Conversion: Oil Industry Conversions
• All to the measuring units

### Converters

• Converters: currencies, lengths, weight, surfaces, temperatures, time, speeds, volumes, bytes…

• the converter: currencies, length, volume, mass, time, fuel, temperature, pressure…
• Conversion of imperial and metric units
• With the country of the maths - Conversion of units of length: allows in particular the conversion of old French units and Russian
• Santos - Conversion Calculator Billion BTU, BOE, Dirty Choke Sizes, Condensate, Cooper Basin Gas, Joule, GJ, KJ, kPa, LNG…
• Online metric conversions - Metric, Imperial and US Customary

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