Physics Class 9 Definitions

Complete collection of key terms, concepts, formulas, and laws from all 9 chapters

Physics Class 9 Definitions

This comprehensive collection contains all key definitions, terms, formulas, and laws from the Class 9 Physics syllabus according to the Punjab Textbook Board. Each chapter is organized systematically with clear explanations and examples.

How to Use This Resource:

  • Click on any chapter in the sidebar to jump directly to its definitions
  • Each term is highlighted for easy reference
  • Important formulas are boxed for quick identification
  • For detailed explanations, visit the individual chapter pages

Chapter 1: Physical Quantities and Measurements

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Physics

The branch of science that deals with the study of matter, energy, and their interactions.

Physical Quantity

A property of a material or system that can be quantified by measurement (e.g., length, mass, time).

Base Quantities

Fundamental quantities that cannot be defined in terms of other physical quantities (length, mass, time, electric current, temperature, amount of substance, luminous intensity).

SI Units:
• Length: meter (m)
• Mass: kilogram (kg)
• Time: second (s)
• Electric current: ampere (A)
• Temperature: kelvin (K)

Chapter 2: Kinematics

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Kinematics

The study of motion of objects without considering the forces that cause the motion.

Equations of Motion:
\( v = u + at \)
\( s = ut + \frac{1}{2}at^2 \)
\( 2as = v^2 - u^2 \)

Acceleration

The rate of change of velocity with time. Unit: m/s²

Chapter 3: Dynamics

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Force

A push or pull that changes or tends to change the state of rest or uniform motion of a body.

Newton's First Law

A body continues its state of rest or uniform motion unless acted upon by an external unbalanced force.

Newton's Laws:
First Law: Law of Inertia
Second Law: \( F = ma \)
Third Law: Action-Reaction

Chapter 4: Turning Effect of Forces

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Torque

The turning effect of a force about an axis of rotation. \( \tau = F \times d \)

Conditions for Equilibrium:
• Sum of all forces = 0 (translational equilibrium)
• Sum of all torques = 0 (rotational equilibrium)

Center of Mass

A point where the whole mass of the body is assumed to be concentrated.

Chapter 5: Work and Energy

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Work

Product of force and displacement in the direction of force. \( W = F \times d \times \cosθ \)

Energy

Capacity to do work. Unit: joule (J)

Forms of Energy:
Kinetic Energy: \( KE = \frac{1}{2}mv^2 \)
Potential Energy: \( PE = mgh \)

Chapter 6: Properties of Matter

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Density

Mass per unit volume. \( \rho = \frac{m}{V} \)

Elasticity Formulas:
Stress: \( \frac{F}{A} \)
Strain: \( \frac{\Delta L}{L} \)
Young's Modulus: \( \frac{Stress}{Strain} \)

Hooke's Law

\( F = kx \)

Chapter 7: Thermal Properties of Matter

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Temperature

A measure of the average kinetic energy of the particles in a substance.

Heat Formulas:
Specific Heat: \( Q = mc\Delta T \)
Latent Heat: \( Q = mL \)

Thermal Expansion

The increase in size of a substance due to increase in temperature.

Chapter 8: Magnetism

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Magnetic Field

The region around a magnet where its magnetic force can be detected.

Magnetic Properties:
Magnetic Flux: \( \Phi = BA \)
Flux Density: \( B = \frac{F}{Il} \)

Electromagnet

A temporary magnet created by passing electric current through a coil.

Chapter 9: Nature of Science

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Scientific Method

A systematic approach to research consisting of observation, hypothesis, experimentation, and conclusion.

Scientific Principles:
Empirical evidence
Testability
Reproducibility

Technology

The application of scientific knowledge for practical purposes.