Understanding Fundamental and Derived units
Fundamental units are the basic units of measurement that cannot be expressed in terms of any other unit, nor can they be broken down into simpler forms. They represent the building blocks of all physical quantities, such as length, mass, and time.
Derived units, on the other hand, are units of measurement obtained by combining fundamental units according to mathematical relationships. For example, velocity is measured in metres per second (m/s), which is derived from the units of length and time.
Understanding System of Units
A system of units refers to a complete set of both fundamental and derived units that are used consistently for measurement in science and daily life. Over time, several systems of units have been developed, four of which are especially notable:
What is the CGS sytem
CGS System (Centimetre–Gram–Second) Widely used in early scientific work, this system measures length in centimetres (cm), mass in grams (g), and time in seconds (s).
What is FPS system
FPS System (Foot–Pound–Second) Also known as the British system of units, it measures length in feet (ft), mass in pounds (lb), and time in seconds (s).
What is MKS system
MKS System (Metre–Kilogram–Second) This system uses the metre (m) for length, kilogram (kg) for mass, and second (s) for time. It became the foundation for the modern SI system.
International System of Units (SI)
International System of Units (SI) An expanded version of the MKS system, the SI system includes seven base units (such as metre, kilogram, second, ampere, kelvin, mole, and candela) and two supplementary units. Together, these provide a standardized framework for scientific and technological work worldwide.
Basic Units
| Quantity | Unit | Symbol | Definition |
|---|---|---|---|
| Length | Metre | m | The metre is defined by taking the fixed numerical value of the speed of light in vacuum, c, as 299,792,458 metres per second. |
| Mass | Kilogram | kg | The kilogram is defined by taking the fixed numerical value of the Planck constant, h, as 6.62607015 × 10−34 J·s. |
| Time | Second | s | The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. |
| Electric Current | Ampere | A | The ampere is defined by taking the fixed numerical value of the elementary charge, e, as 1.602176634 × 10−19 C. |
| Thermodynamic Temperature | Kelvin | K | The kelvin is defined by taking the fixed numerical value of the Boltzmann constant, k, as 1.380649 × 10−23 J·K−1. |
| Amount of Substance | Mole | mol | The mole is defined by containing exactly 6.02214076 × 1023 elementary entities (Avogadro’s number). |
| Luminous Intensity | Candela | cd | The candela is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz as 683 lm·W−1. |