In day to day life we measure the weight of fruits and vegetables, the volume of liquids, the temperature of the body and the speed of vehicles. Quantities such as mass, weight, distance, temperature and volume are called physical quantities. This chapter covers fundamental and derived quantities, area, volume, density and the units used to measure very large distances – the astronomical unit and the light year.
1. Physical Quantities
A value and a unit are used to express the magnitude of a physical quantity. For example, if you walk 2 kilometre every day, '2' is the value and 'kilometre' is the unit used to express the magnitude of distance.
Physical quantities are generally classified into two types:
- Fundamental quantities
- Derived quantities
2. Fundamental Quantities and Units
A set of physical quantities which cannot be expressed in terms of any other quantities are known as fundamental quantities (e.g. length, mass, time). Their corresponding units are called fundamental units.