1.1 Introduction

- Physics is a quantitative science, where we measure various physical quantities during experiments. 

- In our day to day life, we need to measure a number of quantities,

 e.g., size of objects, volume of liquids, amount of matter, weight of vegetables or fruits, body temperature, length of cloth, etc. 

- A measurement always involves a comparison with a standard measuring unit which is internationally accepted. 

- For example, for measuring the mass of a given fruit we need standard mass units of 1 kg, 500 g, etc. 

- These standards are called units. 

- The measured quantity is expressed in terms of a number followed by a corresponding unit, 

e.g., the length of a wire is written as 5 m where m (meter) is the unit and 5 is the value of the length in that unit. 

- Different quantities are measured in different units, 

e.g. length in meter (m), time in seconds (s), mass in kilogram (kg), etc. 

- The standard measure of any quantity is called the unit of that quantity.