Lesson: Wind, Storm and Cyclone

A fire alarm usually detects smoke in case of fire. Where should such an alarm be placed in a room?

(a)   Near the door

(b)   On the floor

(c)   On any wall

(d)   On the ceiling

(d)

Four schematic diagrams are shown in the figure below to depict the direction of sea breeze. Which of them gives the correct direction?

(c)

The figure below shows a child blowing air with a straw near the opening of another straw which has its other end in a soft drink bottle. It was observed that the level of the soft drink in the straw rises up as soon as air is blown over its open end.

Which one of the following best explains the reason for rise in level of the drink?

(a)               Blowing of air decreases pressure over the opening of the straw.

(b)               The straw of the soft drink bottle collapses when air is blown over its open end.

(c)               Blowing of air warms up the air inside the straw.

(d)               Blowing of air increases the pressure on the surface of soft drink in the bottle.

(a)

Following are precautions one must take in case a storm is accompanied by lightning.

(i)                 Do not take shelter under a tree.

(ii)              Do not take shelter under an umbrella with a metallic end.

(iii)            Do not take shelter in open garages, storage sheds, etc.

(iv)             Do not take shelter in a bus in the open.

Which one of these is not correct?

a)      (i)

b)      (ii)

c)      (iii)

d)      (iv)

(d)

Which of the following place is most likely to be affected by a cyclone?

(a)   Mumbai

(b)   Puri

(c)   Goa

(d)   Porbandar

(b)

A curtain is hanging at the entrance of a room. A long corridor runs at right angles to the door that is parallel to the curtain.

If a strong wind blows along the corridor, the curtain will

(a)   Get pushed inside the room.

(b)   Get pushed outside the room.

(c)   Get collected towards one end/swirled.

(d)   Remain unaffected.

(b)

Why is Chandigarh unlikely to be affected by a cyclone?

Cyclones develop over the sea and move over the neighbouring land regions and affect the coastal areas. But Chandigarh is located far away from the sea and so it is unlikely to be affected by a cyclone.

Name the ocean which is mainly responsible to bring rain bearing monsoon winds to Kerala coast in June every year?

Indian Ocean is mainly responsible to bring rain bearing monsoon winds to Kerala coast in June every year.

Fill in the blanks.

(i)     Air around us exerts __________.

(ii)  The moving air is called _________.

(iii)      The main cause of wind movement is uneven ___________ on the earth.

(iv) High speed wind can cause cyclone in regions of___________ pressure.

(i)     Pressure

(ii)  Wind

(iii)      Heating

(iv) Low

State whether the following statements are true or false:

i)       If wind flows from land to the ocean, then it is daytime.

ii)     A very high-pressure system, with very high-speed wind surrounding it forms a cyclone.

iii)   The coast line of India is not vulnerable to cyclones.

iv)   Warm air is lighter than cool air.

i)       False. If wind flows from land to the ocean, then it is night time.

ii)     False. A very low-pressure system, with very high-speed wind surrounding it forms a cyclone.

iii)   False. The coast line of India is extremely vulnerable to cyclones.

iv)   True

To expel hot air out of the kitchen, ‘A’ has an exhaust fan fitted on the window of her kitchen and ‘B’ has a similar exhaust fan fitted on the wall near the ceiling of her kitchen. Which of the exhaust fan will expel the hot air more effectively? Explain why?

When food is cooked in a kitchen, lot of heat is generated. Air, on being heated, becomes lighter and so rises up to the ceiling in the kitchen. To expel the hot air out of the kitchen, it would be more desirable to have an exhaust fan fitted on the wall near the ceiling of the kitchen, as ‘B’ does.

On the other hand, if the exhaust fan is fitted on the window of the kitchen, which means at a lower level, much below the ceiling, then the amount of hot air that is collecting in the region between the window and the ceiling will remain trapped there and will not be expelled. So, ‘A’s’ setup is less effective than ‘B’s’.

Why is it advisable not to shut all the doors and windows during a storm?

A storm has a low-pressure centre which is much lower than the pressure inside a closed house. This might cause the strong winds of the storm to create suction on the walls, windows and roofs and shatter the house by pulling it apart. In order to avoid such a disaster, it is advisable not to shut all the doors and windows during a storm.

A flat in Mumbai with a balcony facing the sea has some clothes hung on a clothes line in the balcony. Towards which direction the clothes will be blown in the afternoon? Explain.

A flat in Mumbai with a balcony facing the sea has some clothes hung on a clothes line in the balcony. In the afternoon, the clothes will be blown in the inward direction, i.e., towards the house as an effect of the sea breeze blowing from the sea towards the land. This sea breeze is generated as a result of difference in air pressure. During the day time, the land gets heated faster than the sea. So, the air above the land becomes hotter than the air above the sea and hot air being light, rises up. The cooler air from above the sea rushes inland to occupy that empty space, causing cool sea breeze to blow from sea to land during the day time.

Figure below shows a diagrammatic representation of trees in the afternoon along a sea coast. State on which side is the sea; A or B?

Give reasons for your choice.

During the day time, the land gets heated faster than the sea. So, the air above the land becomes hotter than the air above the sea and hot air being light, rises up. The cooler air from above the sea rushes inland to occupy that empty space, causing cool sea breeze to blow from sea to land during the day time. The bending of the trees is an impact of the direction of the blowing of the sea breeze. So, the sea is on side B, the direction from which the wind is blowing.

A flag mounted on a flag post near the sea coast flutters in the direction of sea. At what time of the day does this happen $–$ at midnight or in the afternoon?

Since the flag is fluttering in the direction of the sea that means the wind is blowing from the land to the sea. During the night, the land cools faster than the sea. As a result, the air above the land is cooler than the air above the sea. So, at night, the warmer air on the sea has lesser density than the air above the land. The warm air above the sea rises up because it is lighter. The cool air from the land rushes towards the sea causing land breeze to blow at night. So, the flag flutters in the direction of the sea at midnight.

Match Column I with Column II. There can be more than one match.

Column I	Column II
(a) On heating air	(i) Descends
(b) On cooling air	(ii) Expands
	(iii) Contracts
	(iv) Rises

(a)   (ii), (iv)

(b)   (i), (iii)

Paheli kept an empty bottle made of plastic inside a refrigerator. After few hours, when she opened the refrigerator, she found the bottle had collapsed. Explain the possible reason.

When Paheli kept the plastic bottle inside the fridge, even though the bottle was empty, it had a certain volume of invisible air trapped within. On cooling the bottle in the refrigerator, the air inside it too cooled. As cooling reduces the volume of air inside, thereby causing decrease in pressure the bottle collapsed.

When strong/high speed wind blows, an umbrella held upright at times gets upturned. Explain the reason.

High speed winds are accompanied by reduced air pressure. Here, increase in wind speed above the open upright umbrella gives rise to an area of low pressure formed just above the umbrella whereas the air pressure below the umbrella is high. This leads to the sucking up of the umbrella top which thereby at times gets upturned due to the low strength of the umbrella frame which cannot resist the force applied by the strong wind.

Suggest some precautions to be taken to prevent the roof of a tin sheet from flying away during a fierce wind storm.

Increase in wind speed above the roof gives rise to an area of low pressure above the roof. On the other hand, the air pressure below the roof is high. This pushes the roof upwards and leads to the sucking up of a light, tin roof which is not tightly secured and so it gets blown away by the strong wind. In order to prevent the roof of a tin sheet from flying away during a fierce storm the following precautions can be taken:

(i)                 Adequate number of fasteners, like J and U-bolts should be used to brace the sheets with the main structure, that too at reduced spacing.

(ii)              The tin sheets used should be thick gauged because light roofs are easily blown off in high winds.

Describe an activity to demonstrate that warm air is lighter than cool air.

Activity to demonstrate that warm air is lighter than cool air

Experiment

(i)                 Take two paper bags of the same size.

(ii)              Hang the two bags in the inverted position on the two ends of a metal or wooden stick, as shown in the following diagram.

(iii)            Tie a piece of thread in the middle of the stick.

(iv)             Hold the stick by the thread as in a balance.

(v)               Put a burning candle below one of the bags as shown in the diagram.

Observation

The balance of the bags is disturbed. The bag with the candle burning under it rises and so the balance tilts towards the other bag.

Inference

This activity indicates that warm air rises up. As the warm air rises up, it pushes the bag above the candle. This disturbance of the balance suggests that the warm air is lighter than the cold air.

The picture in the figure below shows tree line along the sea coast on an island near the equator. As shown, the tree tops are permanently bent in one direction. Are the trees bent towards the sea or away from it? Explain.

The tree line along the sea coast on an island near the equator shows the tops permanently bent in one direction, i.e., away from the sea, towards the land. This happens because during the day, the sea breeze blows from the sea to the land, thereby affecting the trees.

Identify the names of six natural phenomena from the following word diagram given as in the figure below.