🌪️ Chapter 6 – Pressure, Winds, Storms, and Cyclones
🌟 1. Introduction
- 🌬️ Wind exerts force → doors slam, trees sway, leaves move
- This force is called wind pressure
👉 This chapter explains the relation between:
Pressure + Wind + Storms + Cyclones
⚖️ 2. Pressure
📌 Definition
P = \frac{F}{A}
📏 Unit:
- Pascal (Pa) = N/m²
🧠 Concept (Easy Understanding)
- Narrow straps → more pressure (painful)
- Broad straps → less pressure (comfortable)
- Sharp knife/nail → high pressure → cuts easily
👉 Cloth on head spreads pressure → reduces pain
💧 Pressure in Liquids
📌 Key Points:
- Depends on height of liquid (not shape or volume)
- More height → more pressure
🌊 Important Facts:
- Liquids exert pressure:
- on bottom
- on walls
- in all directions
🏗️ Applications:
- Water tanks kept at height → more pressure in taps
- Dams have broad base → withstand high pressure
🌍 3. Pressure Exerted by Air
🌫️ Atmosphere
Layer of air around Earth containing:
- Nitrogen
- Oxygen
- Carbon dioxide
📌 Air Pressure
Air exerts pressure in all directions
🔍 Examples:
🎈 Balloon:
- Expands because air inside pushes outward
🧲 Rubber Sucker:
- Sticks because outside pressure > inside pressure
⚖️ Magnitude:
- Atmospheric pressure on 15 cm × 15 cm ≈ 225 kg weight
👉 We are not crushed because:
Internal body pressure balances external air pressure
📏 Units:
- Pascal (Pa)
- Millibar (mb)
- Hectopascal (hPa)
🌬️ 4. Formation of Wind
📌 Rule:
Air moves from High Pressure → Low Pressure
🎈 Example:
- Air flows from a high-pressure balloon to low-pressure one
🌊 Sea Breeze & Land Breeze
🌞 Day (Sea Breeze):
- Land heats faster → low pressure
- Wind blows from sea → land
🌙 Night (Land Breeze):
- Land cools faster → low pressure on sea
- Wind blows from land → sea
⚡ Key Point:
👉 Greater pressure difference → stronger winds
💨 5. High-Speed Winds and Pressure
📌 Concept:
High-speed winds → reduce air pressure
🎈 Example:
- Blow between balloons → they move closer
🏠 Effect on Houses:
- Fast wind → low pressure above roof
- Higher pressure inside → pushes roof upward
👉 Roofs may blow away!
✅ Safety Tip:
- Keep doors/windows open
→ reduces pressure difference
⛈️ 6. Storms, Thunder & Lightning
🌩️ (A) Storms
📌 Formation:
- Warm moist air rises
- Cools → condenses → clouds form
🌧️ Storm =
- Strong winds
- Rain / hail / snow
🔊 (B) Thunder
- Lightning heats air suddenly
- Air expands → produces sound
👉 This sound is thunder
⚡ (C) Thunderstorm
📌 Definition:
Storm with thunder + lightning
🔄 Process:
- Warm air rises → low pressure
- Upward & downward winds
- Water droplets collide → charges form
- Opposite charges → discharge → lightning
🌍 Local Names:
- Kalboishakhi → West Bengal, Bihar, Jharkhand
- Bordoisila → Assam
- Mango showers → South India
⚡ (D) Lightning
📌 Definition:
Flash of light due to electric discharge
⚠️ Dangers:
- Fire
- Burns
- Death
🛡️ Safety Precautions:
- Stay away from tall objects
- Sit in low area (crouch position)
- Avoid metal objects
- Stay inside car/bus
⚡ Lightning Conductor
📌 Structure:
- Metal rod on building
- Top → pointed
- Bottom → grounded
🎯 Function:
Provides safe path for electric charges
🌪️ 7. Cyclones
📌 Definition:
Large rotating storm over oceans with strong winds and rain
🔄 Formation Process:
1. Sun heats ocean 🌊
2. Warm moist air rises
3. Air cools → condensation → releases heat
4. Low pressure forms
5. Surrounding air rushes in
6. Earth’s rotation → spinning motion
👉 Forms a cyclone system
🌀 Eye of Cyclone
- Center of cyclone
- Calm area
- Surrounded by strong winds
⚠️ Effects:
- 🌊 Storm surge → floods coastal areas
- 🌧️ Heavy rainfall → floods, landslides
- 🧂 Saltwater damages soil & crops
- 🌳 Trees uprooted
- ⚡ Power cuts
🌪️ Example:
- Cyclone Amphan → ~270 km/h winds
🛡️ Safety Measures:
- Follow Indian Meteorological Department (IMD) alerts
- Use satellite warnings
- Keep emergency kit ready
- Move to cyclone shelters
📌 8. Snapshots (Quick Revision)
⚡ One-Line Points
- Pressure = Force ÷ Area
- Unit = Pascal (Pa)
- Liquids & gases exert pressure in all directions
- Atmospheric pressure is very high
- Winds blow due to pressure differences
- Warm air rises → creates low pressure
- Thunderstorm = storm + thunder + lightning
- Lightning conductors protect buildings
- Cyclones form over warm oceans
- IMD gives cyclone warnings
🎯 Final Conclusion
Pressure plays a key role in:
- Wind formation 🌬️
- Storms ⛈️
- Cyclones 🌪️
🌟 Final Formula:
Pressure Difference → Wind → Storm → Cyclone
🧠 Learning Outcome:
- Understand pressure and its effects
- Explain wind and weather patterns
- Stay safe during storms and cyclones
