NCERT Class 7 Science Chapter 8: Wind, Storms and Cyclones YouTube Lecture Handouts

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NCERT Class 7 Science Chapter 8: Wind, Storms and Cyclones

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Air Exerts Pressure – It Leaves Trees Broken in Cyclone

👉 Take a soft plastic bottle. Fill it with hot water. Empty the bottle and immediately cap it tightly. Place the bottle under running water – some steam in the can condenses into water, reducing the amount of air inside – pressure inside decreases than outside causing compression

  • Roaring boat is easier if the wind blows in same direction

  • Fill air in cycle tube – if overfilled it will burst

👉 High speed winds are accompanied by reduced air pressure - The air pressure, when we blow through the stem, decreases at the mouth of the stem than in the wider portion of the funnel.

- High speed winds are accompanied by reduced air pressure

Air Blown through Funnel

- High speed winds are accompanied by reduced air pressure

2 balloons filled with water on string – blow air between them – they come closer – if pressure between balloons is reduced; pressure outside would push them towards each other

- balloons filled with water on string

Moving Air Creates Low Pressure

- balloons filled with water on string

Paper strip bent upwards – blowing over paper reduced the air pressure above the strip

- Air moves

Air with Paper Strip

- Air moves

  • High speed wind passing over the umbrella creates low pressure. Therefore, the umbrella upturns in high wind

  • Air moves from HP to LP (more the difference, faster it moves)

  • Air expands on heating and contracts on cooling

- Warm air rises up

Heating and Cooling of Air

- Warm air rises up

  • Warm air rises up – it is lighter than cold air (so smoke goes up)

  • Where warm air rises, air pressure is lowered and cold air rushes to fill it creating convection currents

- Wind currents are generated due to uneven heating of earth

Weight of Air

- Wind currents are generated due to uneven heating of earth

Wind Currents Are Generated Due to Uneven Heating of Earth

  • Equator gets maximum heat – warms and air rises

  • Winds don’t move exactly north and south but there is a change in direction – due to rotation of earth

  • Monsoon winds – from Mausam (season) – bring rain

  • In Summer (SW monsoon) – at equator – land gets warm quickly heats and air rises and winds flow from ocean to land (in winter – NE monsoon - it is reversed)

  • Sea breeze – towards land in day (coastal city) – cloth will blow towards house with balcony facing sea

  • Day – wind from sea to land and trees bend towards land

Thunderstorms

  • Develop in hot, humid tropical areas

  • Rising temperature – strong upward rising wind (freeze and fall again)

  • Movement of falling droplets with air create lightning and sound

  • Care – don’t stand under tree; don’t hold umbrella with metallic end; don’t sit near window; car or bus is safe; go inside building

Cyclone

  • Center of cyclone is calm – eye (cloud free with light winds) – around it high speed wind and thick clouds – away from it speed decreases

  • 10-15 km high with 10-30 km diameter

  • Heat released to atmosphere warms air around – air rises and decreases the pressure (so more air rushes in and cycle is repeated)

  • Very LP with intense winds – cyclone (affected by temperature, humidity and wind direction)

Image result for cyclone structure eye eye wall

How Does Pressure Create Hurricane

Image result for cyclone structure eye eye wall

  • Highly destructive – 1st indication is strong winds

  • Water waves are so powerful that its hard to overcome – rising water can be 3 to 12 m

  • Reduces soil fertility

  • Heavy rainfall

  • Flood situations

  • Damage houses and communication

  • Called hurricane in America; typhoon in Japan and Philippines; willy willies in Australia

  • East coast is vulnerable more to cyclone in India (in terms of intensity and frequency)

Tornado

  • Dark funnel cloud that reaches from sky to ground

  • Are weak

  • Speed is 300 km/hr

  • It sucks dust and debris near base

  • Form within cyclones

  • A tornado shelter is a room situated deep inside or underground having no windows

  • One has to bow down on knees protecting head and neck using arms

Safety Measures

  • Forecast and warning service

  • Rapid communication

  • Construct shelters and administrative arrangements

  • Not ignore warnings

  • Make necessary arrangements for household goods

  • Avoid driving on roads

  • Keep phone ready for emergency

  • Don’t drink contaminated water

  • Don’t touch wet switches

  • Don’t pressurize rescue teams with undue demands

  • Cooperate with friends and neighbors

  • Cyclone alert or cyclone watch issued 48 hours in advance

  • Cyclone warning issued 24 hours in advance

  • Monitoring with satellites and radars

  • Self help is best help

  • Don’t shut all doors and windows – to avoid roof being blown away due to LP

- Table of Difference of Temperature

How Does Pressure Create Winds

- Table of Difference of Temperature

Plug potato pieces on both end of test tube – insert pencil on one end - increased air pressure can push things

Pressure of air

Pressure of Air

Pressure of air

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