Notes Chapter 6 Science Curiosity Class 8 CBSE Board

Notes For All Chapters – Science Curiosity Class 8

1. Introduction

• Wind exerts force → causes doors to slam, trees to sway, leaves to rise.
• Force of wind = Wind pressure.
• This chapter explains how pressure, wind, storms, and cyclones are related.

2. Pressure

• Definition: Pressure = Force ÷ Area.
• Unit: Pascal (Pa) = N/m².

Concept:

• Narrow straps = more pressure (painful).
• Broad straps = less pressure (comfortable).
• Sharp edge of knife/nail → cuts easily (high pressure).
• Cloth placed on head while carrying loads spreads pressure.

Examples in liquids:

• Pressure depends on height of liquid column (not shape or volume).
• More water height → more pressure.
• Water tanks are placed high → taps get more pressure.
• Liquids exert pressure on bottom and walls, in all directions.
• Base of dams is broader to withstand large water pressure at bottom.

3. Pressure Exerted by Air

• Atmosphere: Layer of air around Earth (gases: nitrogen, oxygen, carbon dioxide, etc.).
• Air pressure: Air exerts pressure on everything, in all directions.

Examples:

• Balloon inflates because air inside exerts pressure on its walls.
• Rubber sucker sticks to surface because outside air pressure is greater than inside.

Magnitude:

• Atmospheric pressure on 15 cm × 15 cm = 225 kg weight.
• We are not crushed because body’s internal pressure balances outside air pressure.

Units:

• Pascal (Pa).
• Practical: millibar (mb) and hectopascal (hPa).

4. Formation of Wind

• Air moves from high pressure → low pressure regions.

Example:

• Balloon with more air pressure → passes air into balloon with less pressure.

Sea breeze and land breeze:

• Day: Land heats quickly → low pressure on land → wind blows from sea → sea breeze.
• Night: Land cools quickly → low pressure on sea → wind blows from land → land breeze.

Greater the pressure difference → stronger the winds.

5. High-Speed Winds and Pressure

High-speed winds reduce air pressure.

Example: Blowing between two balloons → balloons move closer.

Effect on houses:

• Strong winds create low pressure above roofs.
• Higher pressure inside pushes roofs upward → roofs may blow away.
• Keeping windows/doors open reduces pressure difference and prevents roof damage.

6. Storms, Thunder, Thunderstorm, and Lightning

(a) Storms

• Formed when warm, moist air rises → cools → condenses → clouds form.
• Strong winds + rain/hail/snow = storm.

(b) Thunder

• Lightning heats air suddenly.
• Air expands rapidly → produces loud sound = thunder.

(c) Thunderstorm

• A storm with thunder + lightning.

Process:

• Warm moist air rises → low pressure area.
• Upward & downward winds → rubbing of water droplets and ice.
• Electric charges form in clouds.
• Opposite charges → sudden discharge → lightning.

Local names:

• Kalboishakhi (West Bengal, Bihar, Jharkhand).
• Bordoisila (Assam).
• Mango showers (Kerala, Karnataka, Tamil Nadu).

(d) Lightning

• Flash of light due to sudden electric discharge.
• Lightning heats air → expansion → thunder.
• Dangers: Fire, burns, death.

Precautions:

• Stay away from tall objects.
• Sit in low open area, crouch (not flat).
• Avoid metallic umbrellas and water.
• Safer inside car/bus.

Lightning conductor:

• Metal rod fixed on buildings.
• Top pointed, bottom buried in ground.
• Provides safe path for electric charges.

7. Cyclones

Definition: Large spinning storm over warm oceans with very strong winds and rain.

Formation:

1. Sun heats ocean → warm, moist air rises.
2. Air cools → water vapour condenses → releases heat.
3. Rising continues → low pressure created.
4. Air from surroundings rushes in → also rises.
5. Earth’s rotation causes air to spin.
6. System of clouds + winds + rain = cyclone.

Eye of cyclone: Centre, calm, surrounded by strong winds and heavy rain.

Effects:

• Storm surge → wall of seawater 3-12 m high floods coastal areas.
• Heavy rain → floods, landslides.
• Saltwater → damages soil, crops, drinking water.
• Trees uprooted, roads blocked, power cuts.
• Example: Cyclone Amphan (2020) with 270 km/h winds.

Safety Measures:

• Follow IMD (Indian Meteorological Department) alerts.
• Satellites track cyclones.
• Keep emergency kit ready.
• Move to cyclone shelters.

8. Snapshots (Summary Points)

• Pressure = Force ÷ Area.
• SI unit = Pascal (Pa).
• Liquids and gases exert pressure in all directions.
• Atmospheric pressure surrounds us and is very high.
• Winds blow due to pressure differences.
• Warm air rises → low pressure → cool air rushes in.
• Thunderstorm = storm with thunder and lightning.
• Lightning conductors protect buildings.
• IMD monitors cyclones and gives warnings.