SI Based Unit:
SI Base Units are Standard Units for a scientific measurement made using SI Units. The SI unit stands for Système international d’unités. SI Base Units are direct measurements of a system.
Examples of SI Base Units
| Physical Quantity | SI Base Unit |
|---|---|
| Length | Metre (m) |
| Mass | Kilogram (kg) |
| Current | Ampere (A) |
| Temperature | Kelvin (K) |
| Time | Second (s) |
| amount | mole (mol) |
SI Derived Unit
SI Derived units are units derived using measurements of SI Base Units. SI Derived Units are not direct measurements but can only derived from Known Measurements of SI Base Unit.
Examples of Derived Unit.
Speed is a unit of physical quantity. The SI unit of speed is ms-1. There is no direct measurement for Speed. However Speed can be derived by the following equation.
Speed = Distance Travelled/ Time Taken
Imagine a car travels 5 m in 2 s, and Now have to find the speed of the car.
To find the speed of the care We can apply the equation for Speed,
Therefore the Speed of the car is 5m/2s = 2.5 m/s = 2.5 ms-1.
| Physical Quantity | Derived SI unit |
|---|---|
| Speed | ms-1 |
| force | kg m s-2 |
| acceleration | ms−2 |
| work | N m |
| density | kg m−3 |
| resistance | V A-1 |
| charge | A s |
| pressure | N m-2 |