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Notes Chapter 6 Science Curiosity Class 8 CBSE Board

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Pressure, Winds, Storms, and Cyclones


1. What is Pressure?

– Pressure is the force applied on a unit area.

Formula: Pressure=Force/Area

Pressure=AreaForce​

SI Unit of Pressure = Pascal (Pa) or N/m²

Examples:

A bag with broad straps feels comfortable because the weight is spread over a large area → less pressure.

Narrow straps give more pressure → feel more painful.


 2. Pressure in Liquids

  • Liquids exert pressure on the walls and bottom of the container.
  • Greater the height of the liquid column, greater the pressure at the bottom.

Activities:

  • Balloons bulge the same amount when pipes have same water height – shows pressure depends on height, not width.
  • When we increase water level, balloon bulges more → higher pressure.

Conclusion:

  • Liquid pressure increases with depth.

3. Pressure on Container Walls

Water comes out from holes in a bottle → proves liquid exerts pressure in all directions.

Dams are built wider at the base to handle more pressure at the bottom.


 4. Pressure by Air (Atmospheric Pressure)

Air exerts pressure on all objects – this is called atmospheric pressure.

Example:

  • A balloon inflates because air inside pushes outward.
  • Sucker sticks to wall because outside air pressure is more than inside it.

Why we are not crushed by air pressure?

Because our body’s internal pressure balances the external pressure.


5. Formation of Wind

  • Wind blows from high pressure to low pressure areas.
  • Warm air rises, creating low pressure.
  • Cool air moves in to fill the space → this moving air is wind.

Examples:

  • Sea breeze (day): Land heats → warm air rises → cool air from sea comes in.
  • Land breeze (night): Sea stays warmer → wind blows from land to sea.

 6. High-Speed Wind Lowers Pressure

  • Fast wind creates low pressure area.
  • Blowing between two hanging balloons brings them closer due to low pressure in between.

Real life effect:

  • Strong winds on rooftops create low pressure above → higher pressure below can blow off roofs if not balanced.

 7. Thunderstorms and Lightning

  • Warm air rises → cools → forms clouds → water droplets combine → heavy → rain/hail/snow.
  • Strong wind moves droplets and ice up and down, they rub and get charged.
  • Positive charges go up; negative stay below → lightning occurs when charges meet.
  • Thunder is sound due to hot air expanding.

Lightning Safety:

  • Stay away from trees or water.
  • Do not use metal rods (umbrellas).
  • Safe in a car or bus.

Lightning Conductor

A metal rod placed on buildings to direct lightning safely into the ground.


8. Cyclones

Form over warm ocean water.

Warm moist air rises → cools → condenses → releases heat → makes air rise more.

This creates a low-pressure area → more air rushes in → rotates due to Earth’s rotation → cyclone.

Eye of the cyclone is calm; outer area has strong winds and rain.

Destruction caused:

  • Flooding, trees falling, power cuts, loss of crops, broken roads.

Protection:

  • Weather updates from IMD (India Meteorological Department).
  • Move to cyclone shelters.
  • Keep emergency kits ready.

Key Points to Remember

1. Pressure = Force ÷ Area.

2. SI Unit of Pressure is Pascal (Pa) or N/m².

3. Liquids and gases exert pressure in all directions.

4. Air pressure around us is called atmospheric pressure.

5. Air flows from high pressure to low pressure regions.

6.Wind is caused by difference in air pressure.

7. Warm air rises and creates low pressure, cool air moves in.

8. Sea breeze and land breeze happen due to pressure difference between land and sea.

9. High-speed winds create low pressure, which can blow off weak rooftops.

10. Thunderstorms are caused by warm, moist air rising and forming strong winds and rain.

11. Lightning occurs when opposite charges build up and suddenly meet.

12. Lightning conductors protect buildings by sending charges safely to the ground.

13. Cyclones are strong rotating storms formed over warm ocean water.

14. Eye of the cyclone is calm, but the outer parts have strong winds and rain.

15. Cyclones cause floods, destruction, and power cuts, so we must stay alert and take safety measures.

16. India Meteorological Department (IMD) gives weather updates and cyclone warnings.

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