1.1 Physical Quantities and Their Units
The foundation of physics depends on physical quantities in terms of which the laws of Physics are expressed. Therefore, these quantities have to be measured accurately. These are mass, length, time, velocity, force, density, temperature, electric current, and numerous others.
Physical quantities are often divided into two categories: base quantities and derived quantities. Derived quantities are those which depend on base quantities. Examples of derived quantities are velocity, acceleration, force, etc. Base quantities are not defined in terms of other physical quantities. The base quantities are the independent physical quantities in terms of which the other physical quantities can be defined. Typical examples of base quantities are length, mass and time.
The measurement of a base quantity involves two steps:
- The choice of a standard
- The establishment of a procedure for comparing the quantity to be measured with the standard so that a number and a unit are determined as the measure of that quantity
Measurements must be reliable and accurate so that they can be used easily and effectively.