Science Class 9 — Complete Notes NCERT

Chapter 1: Matter in Our Surroundings

Matter = kuch bhi jiska mass ho aur space ghera ho.

States of Matter:

| Property | Solid | Liquid | Gas | |---|---|---|---| | Shape | Fixed | No fixed shape | No fixed shape | | Volume | Fixed | Fixed | No fixed volume | | Compressibility | Very low | Very low | High | | Diffusion | Very slow | Slow | Fast | | Density | High | Medium | Very low |

Changes of State:

Solid ──[Melting → ]── Liquid ──[Vaporisation → ]── Gas
       ←[ Freezing ]           ←[ Condensation ]

Solid ──[Sublimation → ]── Gas  (dry ice, naphthalene)
Liquid → Gas at surface = Evaporation (below boiling point)

Latent Heat:

• Latent heat of fusion — solid to liquid at melting point (336 kJ/kg for ice)
• Latent heat of vaporisation — liquid to gas at boiling point (2260 kJ/kg for water)

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Chapter 2: Is Matter Around Us Pure?

Pure substance — fixed composition (elements + compounds)
Mixture — two or more substances mixed (homogeneous + heterogeneous)

Separation methods:

| Method | For separating | |---|---| | Evaporation | Salt from water | | Filtration | Insoluble solid from liquid | | Distillation | Two miscible liquids with different BP | | Chromatography | Dyes, pigments, dissolved substances | | Centrifugation | Cream from milk, blood components | | Magnetic separation | Iron from non-magnetic substances |

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Chapter 3: Atoms and Molecules

Atom — smallest particle of an element that can take part in a chemical reaction.

Atomic mass unit (u) = 1/12 mass of C-12 atom

Important atomic masses:

• H=1, C=12, N=14, O=16, Na=23, Mg=24, Al=27, S=32, Cl=35.5, Ca=40, Fe=56

Molecule — smallest particle of substance with independent existence.

Law of Conservation of Mass — mass of reactants = mass of products
Law of Constant Proportions — compound always has same ratio of elements

Mole concept:

1 mole = 6.022 × 10²³ particles (Avogadro's number)
Molar mass = mass of 1 mole in grams = atomic mass in g

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Chapter 4: Structure of the Atom

Bohr's Model:

Nucleus (protons + neutrons) ← central
Electrons ← orbit in fixed energy levels (K, L, M, N...)

Subatomic particles:

| Particle | Charge | Mass | Discoverer | |---|---|---|---| | Proton | +1 | 1 u | Rutherford | | Neutron | 0 | 1 u | Chadwick | | Electron | -1 | 0.0005 u | Thomson |

Electron configuration:

• K shell: max 2 electrons (2n²)
• L shell: max 8 electrons
• M shell: max 18 electrons
• Valence electrons = outermost shell electrons

Isotopes — same Z (protons), different A (mass number) — e.g., ¹²C and ¹⁴C
Isobars — same A, different Z — e.g., ⁴⁰Ca and ⁴⁰Ar

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Chapter 5: The Fundamental Unit of Life — Cell

Cell = basic structural and functional unit of life.

Cell organelles:

| Organelle | Function | |---|---| | Cell wall | Protection, support (plants only) | | Cell membrane | Semi-permeable, controls entry/exit | | Nucleus | DNA storage, controls cell activities | | Mitochondria | Energy production — ATP (powerhouse) | | Chloroplast | Photosynthesis (plants only) | | Ribosome | Protein synthesis | | Endoplasmic reticulum | Transport + lipid synthesis | | Golgi body | Packaging + secretion | | Vacuole | Storage (large in plants) | | Lysosome | Digestion of waste (suicide bags) |

Osmosis = movement of water through semi-permeable membrane from high water concentration to low.

• Hypotonic solution → cell swells (turgid)
• Hypertonic solution → cell shrinks (plasmolysis)
• Isotonic solution → no change

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Chapter 7: Diversity in Living Organisms

Whittaker's 5 Kingdom Classification:

1. Monera — prokaryotes (bacteria, cyanobacteria)
2. Protista — unicellular eukaryotes (Amoeba, Paramecium)
3. Fungi — decomposers (mushrooms, yeast)
4. Plantae — plants (algae to flowering plants)
5. Animalia — animals (porifera to mammals)

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Chapter 8: Motion

Distance vs Displacement:

• Distance — total path length (scalar)
• Displacement — shortest path, with direction (vector)

Speed vs Velocity:

• Speed = distance/time (scalar)
• Velocity = displacement/time (vector)

Equations of motion (uniform acceleration):

v = u + at
s = ut + ½at²
v² = u² + 2as
s = (u+v)t/2

where u=initial velocity, v=final velocity, a=acceleration, t=time, s=displacement

Graphical analysis:

• d-t graph: slope = velocity
• v-t graph: slope = acceleration, area = displacement

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Chapter 9: Force and Laws of Motion

Newton's 3 Laws:

1. Inertia Law — Object stays at rest or uniform motion unless net force acts
2. F = ma — Force = mass × acceleration
3. Action-Reaction — Every action has equal and opposite reaction (different objects)

Momentum p = mv (kg·m/s)
Impulse J = F×t = Δp

Law of Conservation of Momentum:

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
(Total momentum before = Total momentum after collision)

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Chapter 10: Gravitation

Newton's Law of Gravitation:

F = G × m₁ × m₂ / r²
G = 6.67 × 10⁻¹¹ N·m²/kg²

Acceleration due to gravity:

g = GM/R² = 9.8 m/s² (on Earth's surface)

Free fall — object falling under gravity only (no air resistance)

• All objects fall with same acceleration g (Galileo's experiment)

Weight vs Mass:

• Mass = amount of matter (constant everywhere)
• Weight = mg (changes with g — less on moon)

Thrust and Pressure:

Pressure P = Force/Area (Pa = N/m²)

Archimedes' Principle:

Buoyant force = weight of fluid displaced
Object floats if density < fluid density

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Chapter 11: Work and Energy

Work W = F × d × cosθ  (Joules)
No work if: F ⊥ d, or d = 0

Kinetic Energy KE = ½mv²
Potential Energy PE = mgh
Total Energy = KE + PE = constant (conservation)

Power P = Work/Time  (Watts = J/s)
1 kWh = 3.6 × 10⁶ J

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Chapter 12: Sound

Sound — mechanical longitudinal wave, needs medium.

Speed of sound:
  Air (25°C): 346 m/s
  Water: ~1500 m/s
  Steel: ~5100 m/s

Speed = λ × f  (wavelength × frequency)

Human hearing range: 20 Hz to 20,000 Hz
Ultrasound: >20,000 Hz (SONAR, medical imaging)
Infrasound: <20 Hz (earthquakes, elephants)

Echo — reflected sound, needs distance >17m from obstacle

Reverberation — multiple reflections causing prolonged sound

SONAR: Sound Navigation And Ranging

distance = v × t/2

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Chapter 13: Why do we fall ill?

Health — physical + mental + social well-being, not just absence of disease.

Types of diseases:

| Type | Examples | |---|---| | Infectious (communicable) | Cold, TB, cholera, AIDS | | Non-infectious | Diabetes, cancer, hypertension | | Acute | Short duration (cold, malaria) | | Chronic | Long duration (TB, diabetes) |

Pathogens and their vectors:

• Mosquito → Malaria (Plasmodium), Dengue, Filariasis
• Housefly → Typhoid, Cholera
• Sexual contact → AIDS (HIV), Syphilis

Antibiotics work against bacteria, NOT viruses.

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Photosynthesis (Chapter 6)

6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂

Conditions needed:

• Sunlight
• Chlorophyll (in chloroplasts)
• Carbon dioxide (from air through stomata)
• Water (from soil through roots and xylem)