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Wind, storms and cyclone (grade 7 cbse, science)

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fun presentation with riddles. grade 7 cbse. detailed ppt on the cyclone, its causes. impacts, formation, etc.

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Wind, storms and cyclone (grade 7 cbse, science)

  1. 1. A wonderfulA wonderful presentAtion by:presentAtion by:
  2. 2. WINDS,STORMSWINDS,STORMS AND CYCLONESAND CYCLONES
  3. 3. TOPIC :TOPIC :  AIR ISAROUND USAIR ISAROUND US  Air exertspressureAir exertspressure  Air expandson heating and contractsonAir expandson heating and contractson coolingcooling  Warm air lighter than cold airWarm air lighter than cold air  High speed windsareaccompanied by reducedHigh speed windsareaccompanied by reduced air pressureair pressure  formation of cycloneformation of cyclone
  4. 4. INTRODUCTIONINTRODUCTION We know about the formation ofWe know about the formation of clouds and the rains. These areclouds and the rains. These are natural phenomena. Even rain ,natural phenomena. Even rain , thunder , lightning , wind , storms ,thunder , lightning , wind , storms , cyclones , etc., are also naturalcyclones , etc., are also natural phenomena that periodically takephenomena that periodically take place in nature. While many of theseplace in nature. While many of these phenomena are useful or favourablephenomena are useful or favourable to mankind. Some of them areto mankind. Some of them are harmful and cause great destructionharmful and cause great destruction as well. Let us now discuss aboutas well. Let us now discuss about these phenomena.these phenomena.
  5. 5. AIR IS AROUND USAIR IS AROUND US Air is a mixture of colourless, odourless andAir is a mixture of colourless, odourless and tasteless gases.tasteless gases. The layer of air surroundingThe layer of air surrounding the Earth is called atmospherethe Earth is called atmosphere.. Air exerts forceAir exerts force on the earth due its weight.on the earth due its weight. The pressureThe pressure exerted by the air present in the atmosphere isexerted by the air present in the atmosphere is called atmospheric pressure.called atmospheric pressure. Let us see aboutLet us see about two important properties of airtwo important properties of air (i) Air exerts(i) Air exerts pressure, (ii) Air expands on heating [and becomespressure, (ii) Air expands on heating [and becomes lighter].lighter]. Remember that the moving air is calledRemember that the moving air is called wind.wind.
  6. 6. .. A bolt of lightning travels at aA bolt of lightning travels at a speed of more than 400,000 km/h.speed of more than 400,000 km/h. It can heat the air around it to aIt can heat the air around it to a temperature which is more than 4temperature which is more than 4 times the temperature of thetimes the temperature of the surface of the sun. That is whatsurface of the sun. That is what makes lightning so dangerous.makes lightning so dangerous.
  7. 7. (i) Air Exerts Pressure(i) Air Exerts Pressure We know air exerts pressure due to its own weight.We know air exerts pressure due to its own weight. For example:For example:  While rowing a sail boat, we find that it is easier to rowWhile rowing a sail boat, we find that it is easier to row a sail boat in the direction of wind. It is very difficulta sail boat in the direction of wind. It is very difficult to row a sail boat against the direction of wind.to row a sail boat against the direction of wind.  When we are flying a kite, then the wing coming from ourWhen we are flying a kite, then the wing coming from our back side helps the kite to fly higher and higher. It isback side helps the kite to fly higher and higher. It is the blowing wind which exerts the pressure on the kite tothe blowing wind which exerts the pressure on the kite to fly higher.fly higher. All the experiences show’s that wind exerts a forceAll the experiences show’s that wind exerts a force (or pressure) on objects.(or pressure) on objects.
  8. 8. Activity-1Activity-1
  9. 9. (ii) Air Expand On Heating(ii) Air Expand On Heating And Contracts On CoolingAnd Contracts On Cooling When air is heated, its volume increases and itWhen air is heated, its volume increases and it occupies a bigger space. We sayoccupies a bigger space. We say air expands onair expands on heating.heating. When air is cooled, its volume decreases and itWhen air is cooled, its volume decreases and it occupies a smaller space. We sayoccupies a smaller space. We say air contractsair contracts on cooling.on cooling. Let us perform an experiment to understandLet us perform an experiment to understand more….more….
  10. 10. Activity-2Activity-2
  11. 11. Warm Air Is Lighter ThanWarm Air Is Lighter Than Cold AirCold Air We have just learnt that airexpands onWe have just learnt that airexpands on heating. When the airexpands in the balloonheating. When the airexpands in the balloon its mass remains same, but volume increases.its mass remains same, but volume increases. We know density is the ratio of mass andWe know density is the ratio of mass and volumevolume (Density = Mass/Volume).(Density = Mass/Volume). So, if theSo, if the volume of airincreases , mass remains thevolume of airincreases , mass remains the same, the density of airdecreases. So insame, the density of airdecreases. So in conclusion we can say,conclusion we can say, hot airis lighterhot airis lighter (lowerdensity) than cold air(higher(lowerdensity) than cold air(higher density).density). So,So, hot airrises upwards.hot airrises upwards. Conversely, we can sayConversely, we can say cold airis heaviercold airis heavier (higherdensity) than hot air(lowerdensity).(higherdensity) than hot air(lowerdensity). So,So, cold airsinks downward.cold airsinks downward.
  12. 12. ACTIVIy-3ACTIVIy-3
  13. 13. HIGH SPEED WINDS AREHIGH SPEED WINDS ARE ACCOMPANIED BY REDUCEDACCOMPANIED BY REDUCED AIR PRESSUREAIR PRESSURE Moving air is called wind. I t hasMoving air is called wind. I t has been f ound t hat f ast blowingbeen f ound t hat f ast blowing wind creat es a r egion of lowwind creat es a r egion of low pressure. Let us perf orm t hepressure. Let us perf orm t he f ollowing act ivit y t o explain t hatf ollowing act ivit y t o explain t hat f ast blowing wind creat es af ast blowing wind creat es a r egion of low or reduced airr egion of low or reduced air
  14. 14. Activity-4Activity-4
  15. 15. Activity-5Activity-5
  16. 16. Activity-6Activity-6
  17. 17. Some more exampleSSome more exampleS 1.1. When the wind speed is veryWhen the wind speed is very high, the roofs of the huts or tinhigh, the roofs of the huts or tin sheet roofs of the godown aresheet roofs of the godown are blown off. This is because whenblown off. This is because when the high speed winds blow overthe high speed winds blow over the roofs, it reduces the airthe roofs, it reduces the air pressure above the roofs. Thus,pressure above the roofs. Thus, the higher air pressure below thethe higher air pressure below the roof exerts large force to lift uproof exerts large force to lift up
  18. 18. Some more exampleSSome more exampleS 2. The wings of an aeroplane are2. The wings of an aeroplane are designed in such a way that airdesigned in such a way that air above them moves faster than the airabove them moves faster than the air below them. When the aeroplane runsbelow them. When the aeroplane runs on runway in order to take off, theon runway in order to take off, the air above the wings moves faster, theair above the wings moves faster, the air pressure becomes very small asair pressure becomes very small as compared to the pressure below. Thecompared to the pressure below. The resultant upward push or lift makesresultant upward push or lift makes the plane fly. Birds also fly in thethe plane fly. Birds also fly in the
  19. 19. The wind speed is measured by an instrumentThe wind speed is measured by an instrument calledcalled ANEMOMETER.ANEMOMETER. The speed of windThe speed of wind is measured in kilometers per hour. Theis measured in kilometers per hour. The direction of wind at a place is found by usingdirection of wind at a place is found by using an instrument calledan instrument called WIND VANE.WIND VANE.
  20. 20. CYCLONECYCLONE The word ‘CYCLONE’ is derived from theThe word ‘CYCLONE’ is derived from the greek word ‘CYCLOS’ meaning the coilsgreek word ‘CYCLOS’ meaning the coils of a snake.of a snake. A cyclone is a huge revolvingA cyclone is a huge revolving storm caused by very high speed windsstorm caused by very high speed winds blowing around a central area of lowblowing around a central area of low pressure zone over the ocean.pressure zone over the ocean.
  21. 21. Formation oFFormation oF cyclonescyclones The formation of a cyclone is aThe formation of a cyclone is a very complex process. Factorsvery complex process. Factors likelike wind speed, windwind speed, wind direction, temperaturedirection, temperature andand humidityhumidity contribute to thecontribute to the development of cyclones.development of cyclones.
  22. 22. FormaTIoN oF CYCloNeFormaTIoN oF CYCloNe 1.1. The sun heats the surface of ocean-water.The sun heats the surface of ocean-water. The warm water in turn heats the air aboveThe warm water in turn heats the air above it. This causes a low pressure on a vastit. This causes a low pressure on a vast area of the ocean. Due to the lowarea of the ocean. Due to the low pressure, the moist air from the oceanpressure, the moist air from the ocean surface begins to rise rapidly. This createssurface begins to rise rapidly. This creates a strong upward wind that rotates spirally.a strong upward wind that rotates spirally.
  23. 23. FormaTIoN oF CYCloNeFormaTIoN oF CYCloNe 2. As the warm and moist air (containing a2. As the warm and moist air (containing a lot of water vapour) rises high up in thelot of water vapour) rises high up in the atmosphere, it gets cooled and the wateratmosphere, it gets cooled and the water vapour present in it condenses to formvapour present in it condenses to form clouds (called thunder clouds). When waterclouds (called thunder clouds). When water vapuor condenses, it releases heat.vapuor condenses, it releases heat.
  24. 24. FORMATION OFFORMATION OF CYCLONESCYCLONES 3. The heat released by the condensation of3. The heat released by the condensation of water vapour in the atmosphere warms thewater vapour in the atmosphere warms the atmosphere warms the air all around. Thisatmosphere warms the air all around. This warm air rises higher into the atmospherewarm air rises higher into the atmosphere causing a low pressure. More air rushes tocausing a low pressure. More air rushes to the centre of the storm. This cycle isthe centre of the storm. This cycle is repeated.repeated.
  25. 25. FORMATION OFFORMATION OF CYCLONESCYCLONES 4. The chain of events ends with the formation of a4. The chain of events ends with the formation of a very low pressure system with very high-speedvery low pressure system with very high-speed winds revolving around it. The whether conditionwinds revolving around it. The whether condition consisting of a system of high speed windsconsisting of a system of high speed winds revolving around a central area of very lowrevolving around a central area of very low pressure is calledpressure is called cyclonecyclone. The area of verynlow. The area of verynlow pressure at the centre of the cyclone is called itspressure at the centre of the cyclone is called its eye.eye.
  26. 26. FORMATION OF CYCLONEFORMATION OF CYCLONE 5. Once a cyclone is formed, its begins to5. Once a cyclone is formed, its begins to move over the surface of ocean. The speedmove over the surface of ocean. The speed of wind in the cyclone is more than 120of wind in the cyclone is more than 120 kmph. A cyclone needs a constant supplykmph. A cyclone needs a constant supply of warm and moist air. As the cycloneof warm and moist air. As the cyclone reaches the land, the supply of warm andreaches the land, the supply of warm and moist air gradually stops and the cyclonemoist air gradually stops and the cyclone dies down.dies down.
  27. 27. FORMATION OFFORMATION OF CYCLONECYCLONE In theIn the southernsouthern hemisphere,hemisphere, thesethese tropical stormstropical storms are calledare called cyclonescyclones andand rotate in arotate in a clockwiseclockwise direction.direction.
  28. 28. FORMATION OFCYCLONEFORMATION OFCYCLONE In theIn the northernnorthern hemisphere,hemisphere, cyclone arecyclone are calledcalled hurricaneshurricanes andand typhoonstyphoons andand rotate in anrotate in an anticlockwiseanticlockwise direction.direction.
  29. 29. India has a large coastlineIndia has a large coastline which makes itwhich makes it vulnerable to cyclonesvulnerable to cyclones both in terms ofboth in terms of intensity and frequencyintensity and frequency of the cyclones. The eastof the cyclones. The east coast of india, especiallycoast of india, especially the coasts of orissa,the coasts of orissa, andhra pradesh andandhra pradesh and tamil nadu are moretamil nadu are more vulnerable to cyclones.vulnerable to cyclones.
  30. 30. MCQ (ANS IF U KNOW)MCQ (ANS IF U KNOW) 1.1. Which of the following indian stateWhich of the following indian state is vulnerable to cyclone?is vulnerable to cyclone? ans: orissa, tamil nadu, and andhraans: orissa, tamil nadu, and andhra pradeshpradesh 2.2. High speed wind are accompained byHigh speed wind are accompained by _________ ._________ . ans: reduced air pressureans: reduced air pressure 3. The central calm area of a cyclone is3. The central calm area of a cyclone is called __________ .called __________ . ans: eyeans: eye
  31. 31. FILL IN THE BLANKSFILL IN THE BLANKS 1. The layer of air surrounding the ear1. The layer of air surrounding the eart called _______ .called _______ . Ans: atmosphereAns: atmosphere 2. Hot air is _____ than cold air.2. Hot air is _____ than cold air. Ans: lighterAns: lighter 3. Density = ______/Volume3. Density = ______/Volume Ans: massAns: mass
  32. 32. I am scary when at myI am scary when at my best. People run from mebest. People run from me others stay to try andothers stay to try and outlast my wrath. I amoutlast my wrath. I am on news and I pass quickon news and I pass quick as I come, you cantas I come, you cant destroy me, you cantdestroy me, you cant look me in the eye.look me in the eye. What am i?What am i?
  33. 33. I am all around you,I am all around you, but you cannot seebut you cannot see me.me. I have no throat, butI have no throat, but uu can hear me roaring.can hear me roaring. Valued during summerValued during summer but despised in thebut despised in the winter.winter. What am I ?What am I ?

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