Natural Phenomena
Natural Phenomena
Objects and Materials
| Property | Meaning | Example |
|---|---|---|
| Hardness | Ability to resist scratching | Iron, Stone |
| Solubility | Ability to dissolve in water | Salt dissolves, Sand does not |
| Transparency | Allows light to pass or not | Glass (Transparent), Butter paper (Translucent) |
- Metals: Shiny, hard, conduct electricity – Iron, Copper
- Non-metals: Dull, soft, poor conductors – Sulphur, Carbon
- Physical change: No new substance (Melting)
- Chemical change: New substance formed (Rusting)
- Rust prevention: Painting, Oiling, Galvanisation
Memory Tip: Rust needs AIR + WATER. Stop any one to prevent rust.
Exam Tip: Filtration separates insoluble solids from liquids.
Measurement and Motion
| Quantity | Unit | Instrument |
|---|---|---|
| Length | Metre (m) | Scale, Measuring tape |
| Mass | Kilogram (kg) | Weighing balance |
| Time | Second (s) | Clock, Stopwatch |
- Rectilinear: Straight line motion
- Circular: Movement in a circle
- Periodic: Repeating motion
- Uniform motion: Equal distance in equal time
- Non-uniform motion: Unequal distance in equal time
Memory Tip: Speed = Distance ÷ Time
Exam Tip: Horizontal line in distance-time graph shows rest.
Light, Shadows and Reflection
| Object | Type | Example |
|---|---|---|
| Transparent | Fully passes light | Glass |
| Translucent | Partially passes light | Butter paper |
| Opaque | Does not pass light | Wood |
- Pinhole camera forms inverted images
- Plane mirror forms same size image
- Concave mirror: Used in torch, shaving mirror
- Convex mirror: Used in vehicles
- Rainbow is formed due to dispersion of light
Memory Tip: ROYGBIV = Colours of rainbow
Exam Tip: Human eye defect for distant vision = Myopia
Electricity and Circuits
- Basic circuit has cell, switch, wire and bulb
- Conductors: Allow current (Copper, Aluminium)
- Insulators: Do not allow current (Plastic, Rubber)
- Fuse protects circuits from overcurrent
- MCB breaks connection during overload
| Component | Function |
|---|---|
| Battery | Provides electrical energy |
| Switch | Starts or stops current |
| Electric Bell | Works on magnetic effect |
Memory Tip: Closed circuit = Current flows.
Exam Tip: Fuse wire melts first if excess current flows.
Magnetism
| Material | Nature |
|---|---|
| Iron | Magnetic |
| Wood | Non-magnetic |
- Like poles repel, unlike poles attract
- Freely suspended magnet rests in North-South direction
- Magnets should be stored with keepers
- Compass contains magnetic needle
Memory Tip: N-N repel, S-S repel, N-S attract
Exam Tip: Heating or hammering weakens magnets.
Heat and Temperature
| Thermometer | Use |
|---|---|
| Clinical | Measures body temperature |
| Laboratory | Measures other temperatures |
- Units: Degree Celsius, Kelvin
- Heat transfer: Conduction, Convection, Radiation
- Metals are good conductors
- Wood and plastic are poor conductors
Memory Tip: Conduction needs contact, Radiation does not.
Exam Tip: Thermos flask reduces heat loss.
Force, Pressure and Friction
- Force = Push or Pull
- Contact force: Friction, Muscular
- Non-contact force: Gravitational, Magnetic
- Friction opposes motion
| Example | Concept |
|---|---|
| Sharp knife | More pressure due to small area |
| Camel feet | Less pressure due to large area |
Memory Tip: Pressure = Force ÷ Area
Exam Tip: Oil reduces friction in machines.
Sound
- Sound needs medium to travel
- No sound in vacuum
- High pitch = Shrill sound
- Loudness depends on amplitude
| Instrument Type | Example |
|---|---|
| String | Guitar |
| Wind | Flute |
| Percussion | Drum |
Memory Tip: Human audible range = 20 Hz to 20,000 Hz
Exam Tip: Noise pollution harms hearing.
Combustion, Flame and Fuels
- Combustion needs fuel + oxygen + heat
- Rapid, slow and explosive combustion
- Blue flame is hottest
- Fuel efficiency = Energy per unit fuel
| Fuel | Type |
|---|---|
| Coal | Solid |
| Petrol | Liquid |
| LPG | Gas |
Memory Tip: Fire needs triangle: Heat + Fuel + Oxygen
Exam Tip: CO gas is produced during incomplete combustion.
Some Natural Phenomena
- Charging by rubbing produces static electricity
- Like charges repel, unlike attract
- Lightning conductor protects tall buildings
- Earthquakes occur due to movement of tectonic plates
| Disaster | Safety Measure |
|---|---|
| Lightning | Stay indoors, avoid trees |
| Earthquake | Take cover under strong table |
Memory Tip: Rubber sole protects from earth shock.
Exam Tip: Always move to open space during earthquake if safe.