Class 9 Science Complete Notes — Motion, Matter, Cells, Gravitation

PHYSICS

Chapter 1: Motion

Scalar vs Vector:

• Scalar: magnitude only — speed, distance, mass, time
• Vector: magnitude + direction — velocity, displacement, acceleration, force

Key Equations of Motion (Uniform Acceleration):

v = u + at
s = ut + ½at²
v² = u² + 2as
s_n = u + a(2n-1)/2

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

Graphical Analysis:

• Displacement-time graph: slope = velocity
• Velocity-time graph: slope = acceleration; area = displacement

Circular Motion:

• Uniform circular motion has constant speed but changing velocity (direction changes)
• Centripetal acceleration: a = v²/r (directed toward center)

Chapter 2: Newton's Laws of Motion

First Law (Inertia): Objects resist change in their state of motion.

• Inertia of rest, inertia of motion, inertia of direction
• Greater mass = greater inertia

Second Law: F = ma (Force = mass × acceleration)

• 1 Newton = force that gives 1 kg mass an acceleration of 1 m/s²
• Momentum: p = mv
• F = dp/dt = rate of change of momentum

Third Law: Action-reaction forces are equal and opposite

• Act on DIFFERENT bodies (so they don't cancel)
• Examples: rocket propulsion, walking, swimming, jumping

Conservation of Momentum: In absence of external forces, total momentum = constant m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

Chapter 3: Gravitation

Newton's Law of Universal Gravitation: F = Gm₁m₂/r² G = 6.67×10⁻¹¹ N·m²/kg²

g (acceleration due to gravity): g = GM/R² = 9.8 m/s² on Earth's surface

Factors affecting g:

• Altitude: g decreases with height
• Depth: g decreases inside Earth
• Latitude: g slightly more at poles

Mass vs Weight:

• Mass = amount of matter (kg) — constant everywhere
• Weight = mg (Newtons) — varies with location
• Weight on Moon = (1/6)×Weight on Earth

Free Fall: Object falling under gravity only (no air resistance)

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

Escape Velocity: v_e = √(2gR) = 11.2 km/s for Earth

Chapter 4: Work, Energy, Power

Work: W = F·d·cosθ (Joules)

• Positive work: force and displacement in same direction
• Negative work: force opposite to displacement (friction)
• Zero work: force perpendicular to displacement

Kinetic Energy: KE = ½mv²

Potential Energy: PE = mgh

Work-Energy Theorem: Work done = Change in KE = ΔKE

Conservation of Energy: KE + PE = constant (in absence of friction)

Power: P = Work/Time = W/t (Watts) 1 Horsepower = 746 Watts

Commercial Unit of Energy: 1 kWh = 3.6×10⁶ J

Chapter 5: Sound

Properties of Sound:

• Mechanical longitudinal wave (needs medium)
• Speed: 343 m/s in air (at 20°C), faster in solids > liquids > gases

Characteristics:

• Pitch: Related to frequency (high freq = high pitch)
• Loudness: Related to amplitude (large amplitude = loud)
• Timbre: Quality that distinguishes different sources

Human ear range: 20 Hz to 20,000 Hz

• Infrasound: <20 Hz (elephants, earthquakes)
• Ultrasound: >20,000 Hz (bats, medical imaging, SONAR)

Echo: Reflected sound; minimum distance = 17.2 m for echo perception

SONAR: Sound Navigation And Ranging — uses ultrasound to measure underwater depth Distance = (Speed of sound × Time)/2

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CHEMISTRY

Chapter 1: Matter and Its Nature

States of Matter: | Property | Solid | Liquid | Gas | |---|---|---|---| | Shape | Fixed | Takes container | Takes container | | Volume | Fixed | Fixed | No fixed volume | | Compressibility | Very low | Low | High | | Particle spacing | Very close | Close | Far apart |

Changes of State: Solid ↔ Liquid: Melting/Freezing Liquid ↔ Gas: Evaporation-Boiling/Condensation Solid → Gas: Sublimation (dry ice, naphthalene)

Evaporation: Surface phenomenon; increases with temperature, surface area, wind; decreases with humidity

Latent Heat:

• Latent heat of fusion: heat to melt solid without temperature change
• Latent heat of vaporization: heat to vaporize liquid

Chapter 2: Atoms and Molecules

Laws of Chemical Combination:

1. Conservation of Mass: Mass of reactants = mass of products
2. Definite Proportions: Compound always has elements in fixed mass ratio
3. Multiple Proportions: When two elements form more than one compound

Dalton's Atomic Theory: Matter made of tiny indestructible atoms; atoms of same element identical; compounds = atoms in fixed ratios.

Atomic Mass: Relative mass compared to 1/12 of Carbon-12 atom (amu)

Molecular Formula: Shows actual number of atoms — H₂O, CO₂, NH₃, H₂SO₄

Mole Concept:

• 1 mole = 6.022×10²³ particles (Avogadro's number)
• Molar mass = mass in grams of 1 mole
• Number of moles = given mass / molar mass

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BIOLOGY

Chapter 1: Cell — The Unit of Life

Cell Theory:

1. All living things are made of cells
2. Cell is the basic structural and functional unit of life
3. All cells arise from pre-existing cells

Prokaryotic vs Eukaryotic: | Feature | Prokaryotic | Eukaryotic | |---|---|---| | Nucleus | No membrane-bound nucleus | True membrane-bound nucleus | | Size | Smaller (1-10 μm) | Larger (10-100 μm) | | Organelles | Very few | Many membrane-bound organelles | | Examples | Bacteria, cyanobacteria | Plants, animals, fungi |

Cell Organelles:

• Cell wall: Plant cells only; cellulose; gives rigidity and shape
• Cell membrane: Selectively permeable; controls entry/exit
• Nucleus: Control center; contains DNA; has nucleolus (ribosome synthesis)
• Mitochondria: Powerhouse; aerobic respiration; produces ATP; has own DNA
• Chloroplast: Photosynthesis in plants; has chlorophyll; has own DNA
• Endoplasmic Reticulum: Rough (has ribosomes, protein synthesis) and Smooth (lipid synthesis)
• Golgi Apparatus: Packaging and dispatching of proteins
• Ribosome: Site of protein synthesis
• Vacuole: Large in plant cells; stores water, maintains turgidity
• Lysosomes: "Suicide bags"; contain digestive enzymes; clean up old organelles

Osmosis: Movement of water through semi-permeable membrane from low solute (high water) to high solute (low water) concentration.

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Solved PYQs

Q1 (2023): A car starts from rest and accelerates at 5 m/s² for 10 seconds. Find final velocity and distance. v = u + at = 0 + 5×10 = 50 m/s s = ut + ½at² = 0 + ½×5×100 = 250 m

Q2 (2023): Calculate the force needed to give a 5 kg ball an acceleration of 3 m/s². F = ma = 5 × 3 = 15 N

Q3 (2022): What is the weight of a 60 kg person on the Moon? (g on Moon = 1.67 m/s²) W = mg = 60 × 1.67 = 100.2 N (Compare: on Earth W = 60 × 9.8 = 588 N)

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Quick Revision Checklist

• 3 equations of motion: v=u+at, s=ut+½at², v²=u²+2as
• Newton's 3 laws with examples
• F = ma; p = mv; conservation of momentum formula
• g = 9.8 m/s² on Earth; 1/6 on Moon
• Weight = mg (Newtons); Mass = kg (constant)
• W = Fs cosθ; KE = ½mv²; PE = mgh
• Sound: mechanical, longitudinal, 343 m/s in air
• Human hearing: 20 Hz - 20,000 Hz
• 4 states of matter changes with correct terms
• Osmosis: water moves from low to high concentration of solute