CBSE · Class 9
Physics Formulas Class 9
All key formulas for CBSE Class 9 Physics — Motion, Force, Gravitation, Work-Energy and Sound
Ch 1.Chapter 8 — Motion
| Formula / Relation | Expression |
|---|---|
| Speed | v = d/t |
| Average speed | v_avg = Total distance / Total time |
| Velocity | v = displacement/time |
| Acceleration | a = (v − u)/t |
| 1st equation of motion | v = u + at |
| 2nd equation of motion | s = ut + ½at² |
| 3rd equation of motion | v² = u² + 2as |
| Distance-time slope (uniform motion) | Speed = slope of d-t graph |
| Velocity-time slope | Acceleration = slope of v-t graph |
| Displacement from v-t graph | s = area under v-t graph |
Ch 2.Chapter 9 — Force and Laws of Motion
| Formula / Relation | Expression |
|---|---|
| Newton's Second Law | F = ma |
| Momentum | p = mv |
| Newton's Second Law (momentum form) | F = Δp/Δt = (mv − mu)/t |
| Conservation of momentum | m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂ |
| Impulse | J = F × t = Δp |
| Weight | W = mg |
Ch 3.Chapter 10 — Gravitation
| Formula / Relation | Expression |
|---|---|
| Universal Law of Gravitation | F = Gm₁m₂/r² |
| Acceleration due to gravity | g = GM/R² |
| Weight | W = mg |
| Free fall: velocity after time t | v = gt |
| Free fall: distance fallen | h = ½gt² |
| Thrust and Pressure | P = F/A |
| Buoyancy (Archimedes' Principle) | Buoyant force = Weight of fluid displaced |
| Relative density | RD = density of substance / density of water |
Ch 4.Chapter 11 — Work, Energy and Power
| Formula / Relation | Expression |
|---|---|
| Work done | W = F × d × cosθ |
| Work done (force parallel to motion) | W = F × d |
| Kinetic Energy | KE = ½mv² |
| Potential Energy (gravitational) | PE = mgh |
| Conservation of Mechanical Energy | KE + PE = constant (no friction) |
| Power | P = W/t = Energy/time |
| Commercial unit of energy | 1 kWh = 3.6 × 10⁶ J |
Ch 5.Chapter 12 — Sound
| Formula / Relation | Expression |
|---|---|
| Wave speed | v = fλ |
| Time period and frequency | T = 1/f |
| Speed of sound in air (at 0°C) | v ≈ 332 m/s |
| Echo condition | Minimum distance = v × t/2 |
| Minimum distance for echo | d = 332 × 0.1 / 2 = 16.6 m |
| SONAR (echo ranging) | d = v × t/2 |
Frequently Asked Questions
How many Physics chapters are there in Class 9?
CBSE Class 9 Science has 5 Physics chapters: Chapter 8 (Motion), Chapter 9 (Force and Laws of Motion), Chapter 10 (Gravitation), Chapter 11 (Work, Energy and Power), and Chapter 12 (Sound). These are all in the NCERT Class 9 Science textbook.
Which is the most important Physics chapter in Class 9?
Chapter 8 (Motion) and Chapter 11 (Work, Energy and Power) are the most important. Motion introduces the three equations of motion (v=u+at, s=ut+½at², v²=u²+2as) which are tested heavily in Class 9 exams and form the basis for Class 11 Physics kinematics.
What is the formula for Newton's Second Law in Class 9?
Newton's Second Law: F = ma (Force = mass × acceleration). In momentum form: F = Δp/t = (mv − mu)/t. The force is measured in Newtons (N), mass in kilograms (kg), and acceleration in m/s². This is one of the most important formulas in all of Physics.
How to remember all Class 9 Physics formulas?
To remember Class 9 Physics formulas: (1) Understand the concept behind each formula — don't just memorise, (2) Group related formulas together (all Motion equations together), (3) Solve at least 10 numerical problems per chapter, (4) Make a formula card for each chapter and revise weekly, (5) The three equations of motion must be derived from memory — not just memorised.
What is g in Class 9 Physics?
g is the acceleration due to gravity = 9.8 m/s² (or 9.80 m/s²) near Earth's surface. For numerical problems, NCERT Class 9 uses g = 9.8 m/s² unless specified otherwise. Some problems specify g = 10 m/s² for easier calculation. g is NOT the same as G (the Universal Gravitational Constant, which is 6.67×10⁻¹¹ Nm²/kg²).
Related resources
Master Class 9 Physics with Expert Guidance
Class 9 Physics numericals (Motion, Gravitation, Work-Energy) are the foundation for Class 10 and JEE/NEET. Get expert tutoring to build real understanding.
Find a Physics TutorFor reference only. Formulas and information on this page may contain errors or may have been updated since publication. Always verify against your official NCERT textbooks, board-prescribed materials, or the relevant official source before use in exams or assessments. Learnizo is not responsible for any inaccuracies.