Back to: SPM Form 4 Chapter 1 Measurement
Physical Quantities
A physical quantity is a characteristic or property of an object that can be measured or calculated from other measurements. For example: length, mass, speed. The term “quantities” is the short form of the term “physical quantities” and can be used interchangeably.
A unit is a standard for expressing and comparing the measurement of physical quantities. For example: metre (m), kilogram (kg), metre per second (m/s).
SI units are the international system of units which are the standard of units ascribed to each physical quantity.
Base and Derived Quantities
Physical quantities can be classified into base and derived quantities.
Base Quantities
Base quantities are quantities which cannot be derived from any other physical quantity.
There are 7 base quantities:
| Physical Quantity | SI unit |
|---|---|
| length | metre (m) |
| time | second (s) |
| mass | kilogram (kg) |
| electric current | Ampere (A) |
| temperature | Kelvin (K) |
| amount of substance | mole (mol) |
| luminous intensity | candela (cd) |
Derived Quantities
Derived quantities are physical quantities which can be derived from other physical quantities through multiplication or division (or both).
For example:
| Derived Quantity | Formula for derivation |
|---|---|
| Area of a rectangle (m2) | length x width (m x m) |
| Volume of a cube (m3) | length x width x height (m x m x m) |
| Speed (m/s) | distance / time (m / s) |
| Density (kg/m3) | mass / volume (kg / (m x m x m)) |
| Force (N) | mass x acceleration (kg m / s2) |