Units and Measurement

Units and Measurement

1.1 Introduction

• Measurement involves comparing a physical quantity to a standard unit.

• The result is expressed as a number and a unit.

• Physical quantities can be fundamental or derived.

  • Fundamental quantities: Independent and not expressible in terms of others (e.g., length, mass, time).

  • Derived quantities: Expressible in terms of fundamental quantities (e.g., volume, velocity, force).

Fundamental and Derived Units

• Fundamental units are for fundamental quantities.

• Derived units are combinations of base units.

1.2 The International System of Units

• A system of units includes both base and derived units.

• Examples of unit systems:

  • CGS: centimetre, gram, second

  • FPS: foot, pound, second

  • MKS: metre, kilogram, second

• In 1971, the General Conference on Weights and Measures created the Système Internationale d’ Unites (SI).

• The SI system is used internationally for scientific, technical, industrial, and commercial purposes.

• It consists of seven base units and two supplementary units.