Telangana Project

Physics is a science of measurement. Every observation or phenomenon in the physical world can be described using physical quantities. These quantities are essential for understanding and expressing the laws of nature mathematically. Below is a structured explanation of physical quantities:

What Are Physical Quantities?

A physical quantity is any property of matter or energy that can be measured or quantified. It consists of two components:

Magnitude: The numerical value of the quantity.
Unit: The standard used to measure the quantity.

For example:

"The length of a table is 5 meters."
- Magnitude: 5
- Unit: meters

Types of Physical Quantities

Physical quantities are classified into two main categories:

1. Fundamental Quantities

These are the basic quantities that cannot be derived from other quantities. They form the foundation of all measurements.

Examples: Length, Mass, Time, Temperature, Electric Current, Luminous Intensity, Amount of Substance.

2. Derived Quantities

These are quantities that can be expressed in terms of fundamental quantities.

Examples: Speed (derived from length and time), Force (derived from mass, length, and time), Area, Volume, etc.

Units of Measurement

To ensure consistency in measurements, scientists use standardized systems of units. The most widely accepted system is the International System of Units (SI).

1. SI Units for Fundamental Quantities

Physical Quantity	SI Unit	Symbol
Length	Meter	m
Mass	Kilogram	kg
Time	Second	s
Temperature	Kelvin	K
Electric Current	Ampere	A
Luminous Intensity	Candela	cd
Amount of Substance	Mole	mol

2. SI Units for Derived Quantities

Derived quantities are expressed using combinations of fundamental units.

Example:
- Speed = Distance ÷ Time → Unit: m/s
- Force = Mass × Acceleration → Unit: kg·m/s² (also called Newton, N)

Systems of Units

Before the adoption of SI units, various systems were used globally. Here’s a comparison:

System	Length	Mass	Time
SI (Modern)	Meter (m)	Kilogram (kg)	Second (s)
CGS (Older)	Centimeter (cm)	Gram (g)	Second (s)
FPS (British)	Foot (ft)	Pound (lb)	Second (s)

Quick Recall Points

Physical Quantity: Consists of magnitude and unit.
Fundamental Quantities: Cannot be derived (e.g., length, mass, time).
Derived Quantities: Expressed in terms of fundamental quantities (e.g., speed, force).
SI Units: Standardized system of measurement (e.g., meter, kilogram, second).

Unit 1.2 – Physical Quantities