Measurements of physical quantities are expressed in terms of units, which are standardized values. There are two major systems of units used in the world: SI units (also known as the metric system) and English units (also known as the customary or imperial system). English units were historically used in nations once ruled by the British Empire and are still widely used in the United States. Virtually every other country in the world now uses SI units as the standard.
What’s a fundamental unit?
Fundamental units are the units of the fundamental physical quantities in SI system which are not formed from other units. In other words, they are quantities which are independent and don’t depend upon other quantities for their measurement. There are a total of seven fundamental units in the International System of Units. The units include:
- The meter (symbol: m), used to measure length.
- The kilogram (symbol: kg), used to measure mass.
- The second (symbol: s), used to measure time.
- The ampere (symbol: A), used to measure electric current.
- The kelvin (symbol: K), used to measure temperature.
- The mole (symbol: mol), used to measure amount of substance or particles in matter.
- The candela (symbol: cd), used to measure light intensity.
What’s a derived unit?
A derived unit is a unit that results from a mathematical combination of SI base units. They quantities depend upon other fundamental quantities for their measurement. Derived units are either dimensionless or else are the product of base units.
In other words, Derived units are all those units which are obtained by multiplying and/or dividing one or more fundamental units with or without introducing any other numerical factor.
There is a total of 22 derived units. They include:
- Meter per second (distance)
- Mole per cubic meter (amount of substance concentration)
- Specific volume (cubic meter per kilogram).
- Heat (J)
- Force (N)
- Power (W)
- Energy (J)
- Velocity (m/s)
- Density (kg/m3)
- Momentum (kg-m/s)
- Acceleration (m2/s)
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Fundamental Vs Derived Units In Tabular Form
| Fundamental Unit | Derived Unit |
|---|---|
| Fundamental units are all those units which are independent of any other unit (including themselves). | Derived units are all those units which are obtained by multiplying and/or dividing one or more fundamental units with or without introducing any other numerical factor. |
| Fundamental units cannot be further reduced to elementary level; in fact, these are elementary units. | Derived units can be reduced to its elementary level, which are composed of fundamental units. |
| Fundamental units cannot be expressed in terms of derived units. | Derived units can be expressed in terms of fundamental units. |
| Only seven fundamental units exist in Metric System or SI system. | There exist a large number of derived units in Metric System. |
| Examples of seven fundamental units, their abbreviation and corresponding physical properties are as follows: Length (Meter, m) Mass (Kilogram, kg) Time (Second, s) Temperature (Kelvin, K) Amount of substance (Mole, mole) Electric current (Ampere, A) Luminous intensity (Candela, cd) | Examples of few derived units along with corresponding physical properties are: Velocity (m/s) Acceleration (m2/s) Momentum (kg-m/s) Force (N) Density (kg/m3) Heat (J) Energy (J) Power (W), etc. |
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