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 to expand and view 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
Physical Quantities
Quantities that can be measured directly or indirectly using tools and instruments.
SI Units
A system of measurement consisting of seven base units: meter (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount), candela (luminous intensity).
Measurement Tools:
• Metre rule (least count: 1 mm)
• Vernier Calliper (least count: 0.1 mm)
• Screw gauge (least count: 0.01 mm)
• Stopwatch (least count: 0.1 s)
📗 Chapter 2 – Kinematics
Motion Types
Translatory, rotatory, vibratory, linear, random, and circular motion.
Scalar vs Vector
Scalar quantities have magnitude only; vector quantities have both magnitude and direction.
Kinematic Equations:
\( v = u + at \)
\( s = ut + \frac{1}{2}at^2 \)
\( 2as = v^2 - u^2 \)
Speed = \( \frac{Distance}{Time} \), Velocity = \( \frac{Displacement}{Time} \)
📙 Chapter 3 – Dynamics
Newton's Laws of Motion
1st: Law of inertia, 2nd: F=ma, 3rd: Action-reaction pairs.
Force Types
Contact forces (friction, normal, tension) and non-contact forces (gravity, electromagnetic).
Key Formulas:
• Force: \( F = ma \)
• Momentum: \( p = mv \)
• Impulse: \( F \times \Delta t \)
• Weight: \( w = mg \)
📕 Chapter 4 – Turning Effect of Forces
Torque/Moment of Force
The turning effect of a force about an axis of rotation. \( \tau = F \times l \)
Equilibrium
A body is in equilibrium when net force and net torque are both zero.
Key Concepts:
• Principle of moments
• Center of gravity and center of mass
• Stable, unstable, and neutral equilibrium
• Couple: Two equal and opposite parallel forces
📔 Chapter 5 – Work and Energy
Work
Product of force and displacement in the direction of force. \( W = F \times S \times \cos\theta \)
Energy Forms
Kinetic, potential, chemical, thermal, nuclear, and renewable energy sources.
Energy Formulas:
• Kinetic Energy: \( E_k = \frac{1}{2}mv^2 \)
• Potential Energy: \( E_p = mgh \)
• Power: \( P = \frac{W}{t} \)
• Efficiency: \( \frac{\text{Useful output}}{\text{Total input}} \times 100\% \)
📒 Chapter 6 – Properties of Matter
Elasticity
Property of solids to return to original shape after deforming force is removed.
Pressure
Force exerted normally per unit area. \( P = \frac{F}{A} \)
Key Formulas:
• Density: \( \rho = \frac{m}{V} \)
• Pressure: \( P = \frac{F}{A} \)
• Hooke's Law: \( F = kx \)
• Liquid Pressure: \( P = \rho gh \)
📚 Chapter 7 – Thermal Properties of Matter
Temperature vs Heat
Temperature measures hotness/coldness; heat is energy transfer due to temperature difference.
Thermometers
Liquid-in-glass thermometers and thermocouples for temperature measurement.
Temperature Scales:
• Celsius: 0°C (ice point) to 100°C (steam point)
• Fahrenheit: 32°F to 212°F
• Kelvin: 273 K to 373 K (absolute scale)
• Absolute Zero: -273°C or 0 K
📖 Chapter 8 – Magnetism
Magnetic Properties
Like poles repel, unlike poles attract. Magnetic field lines from N to S pole.
Electromagnetism
Electric current produces magnetic field. Right-hand grip rule determines direction.
Magnetic Materials:
• Ferromagnetic (iron, nickel, cobalt)
• Paramagnetic (aluminum, lithium)
• Diamagnetic (copper, bismuth)
• Temporary vs permanent magnets
📙 Chapter 9 – Nature of Science
Scientific Method
Systematic approach: Observation → Hypothesis → Experiment → Theory → Law.
Physics Branches
Mechanics, thermodynamics, optics, electromagnetism, quantum mechanics, relativity.
Interdisciplinary Fields:
• Biophysics
• Medical Physics
• Astrophysics
• Geophysics
• Climate Physics
• Computational Physics