Physical Quantities
Physical quantities are the quantities that can be measured. Length, mass, time and volume are examples of physical quantities.
Physical quantities have two things in common: magnitude and unit. Magnitude represents the size or amount of a quantity, while the unit is the standard used to express its measurement. For example, when measuring a brick, its length, width, height and mass are physical quantities.
Types of Physical Quantities
Physical quantities are classified into two types:
1. Fundamental Physical Quantities
Fundamental physical quantities are independent quantities that cannot be expressed in terms of other physical quantities. Their units are called fundamental units.
There are seven fundamental physical quantities in the International System of Units (SI). 
| Fundamental Quantity | SI Unit | Symbol |
|---|---|---|
| Length | Metre | m |
| Mass | Kilogram | kg |
| Time | Second | s |
| Temperature | Kelvin | K |
| Electric current | Ampere | A |
| Amount of substance | Mole | mol |
| Luminous intensity | Candela | cd |
2. Derived Physical Quantities
Derived physical quantities are quantities that depend on one or more fundamental quantities. They are obtained by combining fundamental quantities mathematically through multiplication, division or other mathematical operations. Their units are called derived units.
Examples of derived physical quantities include area, volume, speed, density and force.
| Derived Quantity | Relationship | SI Unit |
|---|---|---|
| Area | Length × Width | Square metre (m²) |
| Volume | Length × Width × Height | Cubic metre (m³) |
| Speed | Distance ÷ Time | Metre per second (m/s) |
| Density | Mass ÷ Volume | Kilogram per cubic metre (kg/m³) |
| Force | Mass × Acceleration | Newton (N) |
For example, area is a derived physical quantity because it is calculated by multiplying length by width. Similarly, speed is calculated by dividing distance travelled by the time taken.
