A standard unit of measurement is a quantifiable language that describes the magnitude of the quantity. It helps to understand the association of the object with the measurement. Although measurement is an important part of everyday life, kids don’t automatically understand the different ways to measure things. In this article, we will discuss in detail the different units and measurement and why we need them.
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Need For Standard Units and Measurement?
Imagine a situation when a man wants to buy a red coloured shirt, so he goes to a store. The shopkeeper speaks only English. The man says, “Ureed qameesan ahmar allawn”. The shopkeeper says, “What?!” The man asked for a red coloured shirt, but he said it in Arabic. Obviously, the shopkeeper couldn’t understand anything since it was not a standard language.
Similarly, there are many systems and units in place for measuring different quantities like length, area, mass, volume and other things. For example, an acre is a common way of representing area measurement in India. One acre is around 4046 square meters if you look at the metric system. So now you can guess how difficult it would be if there were no standard units and measurement.
Similarly temperature is measured in degree celsius and the same unit of measurement cannot be used to measure the length of a rod. Each quantity has to be measured in its own way. Magnitude and the measurement varies along with the quantity. Hence the need for the units of measurement for each quantity arises.
Also, read about using Dimensional Analysis to convert units.
Read more about: Unit conversion
What is the International System of Units?
After learning the importance of units and measurements, let us focus on the International System of Units. Traditionally, people didn’t have any measuring devices to calculate standard measurement units. To tackle this problem they came up with different innovative ways of measuring with the tools available at hand. For example, they used a foot as a measurement of length. 1 foot is around 0.3 meters which is 30 cm. Another measurement our ancestors used for length was a league. One league was the amount of distance covered by a person when we walked for an hour. This unit, however, is no longer in use.
To tackle this problem of different systems of measurement (just like the different languages), a system of units called the International System of Units was established and has been adopted by most developed and developing countries. Although this has been established and adopted across major fields like science and technology and government operations, normally people still refer to their customary or traditional units. For example, in the United States of America people even now refer to lengths in terms of inches and feet instead of centimetres and meters.
International System of Units
The International System of Units or SI units defines standard units for measurement of all physical quantities.
In principle, any physical quantity can be expressed in terms of seven base units.
| Property | Unit | Symbol |
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric Current | Ampere | A |
| Temperature | Kelvin | K |
| Amount of Substance | mole | mol |
| Luminous Intensity | candela | cd |
Derived Units
Apart from the base units, there are SI units of derived units. These are called as such because their value is determined based on one or more base units. Some examples are given below.
- Frequency – Hertz (Hz); 1 Hz = 1 s-1
- Power – Watt (W); 1 W = 1 kg·m2s−3
SI Unit Prefixes
The SI system utilizes a standard system of prefixes to the basic units that allow them to be more relevant to and descriptive of relative magnitude. Prefixes are used to identify the multiples or the fractions of the original unit. There are 20 accepted prefixes. The table below lists the standard prefixes for the SI units of measurement
Frequently Asked Questions – FAQs
Can a quantity have dimensions but no units associated with it?
No. If a quantity has dimensions then it should have units associated with it.
What are the dimensions of a physical quantity?
Dimensions of a physical quantity refer to the nature of quantity which defines it in some measurable terms. The physical dimensions are expressed in terms of length, mass and time represented by L, M and T respectively.
Define a unit
Any given physical quantity is measured in comparison to a basic unit that is arbitrarily chosen, internationally accepted. The result of a measurement is expressed by a number which is accompanied by a unit.
What are supplementary units?
Supplementary units are dimensionless physical quantities that are used along with fundamental units.
Give an example of Derived units.
Velocity is a physical quantity derived from fundamental quantities of length and time.
The unit of velocity is ms-1.
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