Physical quantity and units

Nine Standard >> Physical quantity and units

Physical Quantity and Units – Class 8 Science

In science, we measure many things like length, weight, time, and temperature. These things that we can measure are called physical quantities. To measure them correctly, we use units.

What is a Physical Quantity?

A physical quantity is anything that can be measured. Examples include:

Length
Mass
Time
Temperature
Speed
Volume

Types of Physical Quantities

Fundamental Quantities: These are the basic physical quantities that are independent and cannot be derived from any other quantity. Example: length, mass, time.
Derived Quantities: These are made by combining two or more fundamental quantities. Example: speed (distance/time), area (length × breadth).

What is a Unit?

A unit is a standard quantity used to measure physical quantities. For example, we measure length in metres, mass in kilograms, and time in seconds.

SI Units (International System of Units)

SI units are the internationally recognized system of measurement used worldwide. Here are some common SI units:

Physical Quantity	SI Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Electric current	ampere	A
Luminous intensity	candela	cd
Amount of substance	mole	mol

Why Are Units Important?

Units help in comparing and understanding measurements easily.
Without proper units, measurements would be meaningless.
They bring uniformity and accuracy in science and everyday life.

Fun Fact

The SI system was officially adopted in 1960 by the 11th General Conference on Weights and Measures.

Conclusion: Units and physical quantities form the basic framework for all scientific measurements. By using standard units, we can make accurate and meaningful observations and comparisons in science and daily life.