Stuck on a Class 9 physics numerical because you cannot recall the right formula? This page is your single starting point for every Class 9 physics formula.
It links to three focused formula pages — one for forces and motion, one for work, energy, and simple machines, and one for sound waves — so you reach the exact formula sheet you need in one tap.
Each page lists the chapter’s key formulas, the SI units and symbols for every variable, worked examples with full substitution, and the common mistakes that cost marks. If you are revising for another class too, the main physics formulas hub collects the formula pages for every class in one place.
Class 9 Physics Formulas – Chapter Directory
Three formula pages cover the entire Class 9 physics syllabus. Choose the chapter you are revising — each page works as a standalone formula sheet for that topic.
Here is what each page actually covers, so you land on the right one:
| Ch | Chapter notes | Key topics covered |
|---|---|---|
| 6 | How Forces Affect Motion (coming soon) | Coming soon |
| 7 | Work, Energy, and Simple Machines (coming soon) | Coming soon |
| 10 | Sound Waves: Characteristics and Applications (coming soon) | Coming soon |
- How Forces Affect Motion — Newton’s laws, force, mass, acceleration, and momentum. Use these formulas to calculate net force, acceleration, and the effect of unbalanced forces.
- Work, Energy, and Simple Machines — work done, kinetic and potential energy, power, and the mechanical advantage of simple machines. Apply them to energy conservation and machine efficiency problems.
- Sound Waves: Characteristics and Applications — frequency, wavelength, speed, amplitude, and the echo formula. Use them to solve problems on sound propagation, reflection, and applications such as sonar.
How to Use These Formula Pages
A formula page is a revision tool, not a substitute for the chapter. Use it in this order:
- Read the formula page after studying the chapter, not before — the formulas make sense only when you already know the concepts they come from.
- Start with the symbol legend. Identify what each variable stands for and its SI unit before you substitute anything.
- Write each formula by hand three times, saying the units aloud. Writing “v = u + at, with v and u in m/s, a in m/s², t in s” fixes the formula and its units in memory together.
- Solve the worked examples step by step to see how substitution happens, then try one yourself without looking.
- Read the common-mistakes section last so you know which errors to check before you submit your answer.
When more than one formula seems to fit, ask what the question gives you and what it asks for:
| What you have | What you need | Formula to use |
|---|---|---|
| Force and mass | Acceleration | F = ma |
| Work done and time taken | Power | P = W/t |
| Mass and height above ground | Potential energy | P.E. = mgh |
| Mass and speed | Kinetic energy | K.E. = ½ mv² |
| Frequency and wavelength of a wave | Wave speed | v = fλ |
| Initial velocity, acceleration, displacement | Final velocity | v² = u² + 2as |
When you know the mass and the change in speed over a distance, use the work-energy theorem (work done = change in kinetic energy, W = ½mv² − ½mu²). Use the power formula P = W/t only when time is given — no time in the question usually means the power formula is the wrong choice.
If a formula or definition feels unclear, open the official NCERT Class 9 Science textbook to read the derivation, and check the CBSE curriculum page to confirm which topics are in your syllabus.
What’s Inside Each Formula Page
All three pages follow the same structure, so you can move through them quickly:
- A formula table for the chapter with the SI unit of every quantity
- A symbol legend explaining each variable
- 2–3 original worked examples with full substitution
- A common-mistakes section showing wrong and corrected working
- Exam-smart tips for presenting answers cleanly
Here is how the symbol legend works, using the first equation of motion as an example:
| Symbol | Quantity | SI unit |
|---|---|---|
| v | Final velocity | m/s |
| u | Initial velocity | m/s |
| a | Acceleration | m/s² |
| t | Time | s |
Numericals usually need SI units before substitution. Keep this conversion table handy:
| Quantity | Common unit | SI unit | Conversion |
|---|---|---|---|
| Speed / velocity | km/h | m/s | 1 km/h = 5/18 m/s |
| Force | kgf | N | 1 kgf = 9.8 N |
| Work / energy | kWh | J | 1 kWh = 3.6 × 10⁶ J |
| Power | horse power | W | 1 hp = 746 W |
| Frequency | kHz | Hz | 1 kHz = 1000 Hz |
Sound is an exception on this table: loudness is compared in decibels (dB), while sound intensity — the sound energy passing per second through unit area — is measured in W/m².
Common mistake: substituting without converting units
Wrong working: A bus travels 36 km in one hour. A student writes v = 36 km ÷ 1 h = 36 km/h and stops there. The answer is not in SI units.
Corrected: Convert first: 36 km = 36,000 m and 1 h = 3,600 s. Then v = 36,000 ÷ 3,600 = 10 m/s. If the final unit is not the SI one, the conversion was missed.
Another frequent error is using v² = u² + 2as without squaring the velocities. Square u and v first, rearrange for the unknown, and take a square root only if v is the unknown.
How marks are allocated in numericals
Most Class 9 school exam marking schemes split a numerical question’s credit into three parts: the formula written with correct symbols and units, the substitution of values in SI units, and the final answer with its unit. Write the formula first even if you cannot finish the arithmetic — it earns partial credit.
Frequently Asked Questions
Do I need to memorize all formulas from Class 9 Physics?
No. Rote memorising formulas without understanding the variables is how formulas get mixed up. Learn what each symbol stands for, its SI unit, and the situation it applies to; the formulas you use often will be memorised naturally while solving problems.
How can I remember formulas for exams without confusion?
Group the formulas by chapter, write each one by hand several times while saying the units aloud, and immediately solve one worked example using it. When two formulas look similar, compare their symbol legends — a different variable usually means a different situation.
What is the most common mistake students make when using physics formulas?
Substituting values without converting to SI units first — leaving speed in km/h when the formula needs m/s, or time in minutes instead of seconds. Convert first, substitute second, and check that the unit of the final answer makes sense.
Which formulas from Class 9 are most frequently asked in board exams?
Class 9 does not have a CBSE board exam, so these formulas are tested in school annual exams and reappear in Class 10. The equations of motion (v = u + at, s = ut + ½at², v² = u² + 2as), F = ma, W = Fs, P.E. = mgh, K.E. = ½mv², P = W/t, and v = fλ are used most often.
Reference: NCERT textbooks (CBSE).