TS 7th Class Science Guide 8th Lesson Air, Winds and Cyclones

TS Board Telangana SCERT Class 7 Science Solutions 7th Lesson Electricity: Current and it’s Effect Textbook Questions and Answers.

TS 7th Class Science 7th Lesson Questions and Answers Telangana – Electricity: Current and it’s Effect

Fill in the missing words in the blank spaces in the following statements:

1. Wind is the air.
2. Winds are generated due to on the earth.
3. Near the earth’s surface air rises up where as air comes down.
4. Air moves from a region of pressure to a region of pressure.
Answer:
1. moving
2. expansion of air
3. hot, cool
4. high, low

Question 5.
Suggest two methods to find out wind direction at a given place.
Answer:

• Flying kites in the air enables us to know the direction of the wind. Naturally, the kite flies only along the direction of the wind to which it blows.
• Whirling of paper fan against the direction of blowing of wind. The above two methods help us to find out wind direction at a given place.

Question 6.
State two experiences that make you think that air exerts pressure. (Other than those given in the text).
Answer:
A. We can understand that air exerts pressure by doing the following two experiments.

• Hot water is poured in the plastic bottle. It is noticed that the temperature of the hot water is between 500C-60°C.
• The mouth of the bottle is closed with lid.
• Then the bottle is shaken to all sides.
• Lid is opened and the water is thrown away from the bottle. Again the bottle is recapped.
• Finally, it is observed that the sides of the bottle are pulled inwards. This proves that air has sideward pressure.

B. I collected a glass beaker, a glass tumbler, a coloured plastic ball and water.
Procedure:

• The glass beaker is filled with water more than half its capacity.
• The collected ball is immersed in the water beaker.
• It is observed that the ball floats on the water.
• A glass tumbler is inverted on the ball.
• We observed the ball goes down to the bottom along with glass tumbler.
• The rim of the glass tumbler remains on the surface itself. This shows that the air in the glass thrusts the water downwards.

Question 7.
While constructing a house, where do we construct ventilators, why?
Answer:

• Naturally we construct the ventilators above the windows, near the roof of house.
• The ventilators facilitate exhaustion of our exhaled air.
• When we breath out air, it goes up and expels out of the house through the ventilators.
• The air we breath out from the lungs is hot in its nature. Infact hot air possess less density.
• When density of air decreases it becomes less in weight.
• As a result the expired air goes up and is expelled out of the house through ventilators.

Question 8.
Explain why holes are made in banners and hoardings hanging in the open.
Answer:

• Holes are made in banners and hoardings which hang in the open air of the streets or grounds.
• When wind blows. it exerts pressure and force on the banner.
• The exerting pressure and force of the wind sometimes may damage the tied rope and cut the banner.
• If holes are made in the banner, the air passes through them easily.
• The holes reduce the force and pressure of the air and retain the banner to hang freely.

Question 9.
How will you help your neighbours in case cyclone approaches your village / town?
Answer:
I can help my neighbours during cyclones by the following way,

• I advice them not to come out of the houses during thunder storms.
• If houses are collapsed, I try to send the victims to the rehabilitation centres.
• T participate in the distribution of food, water and other necessities needed to the victims along with the public servants.
• Even if any one is injured. I take him/her to the nearest health centre or will call the doctor to the specific area.
• I participate in the removing of collapsed trees and any debris.
• I can console the victims to relieve them from mental stress and agony.

Question 10.
In the day time, when we go to the sea, the air blows towards us and does not go towards the sea. Explain.
Answer:

• In the day time, when we go to the sea, the air blows towards us and does not go towards the sea.
• Because, the land heats up faster than the sea. So warm air raises over the land during the day.
• The hot air goes up and the pressure decreases on land.
• As a result the cool air from the surface of sea blows into the land.
• The cool air exerts more pressure.
• The air from high pressure areas to low pressure area keeps the wind blowing from sea surface o land during day time.

Question 11.
Which of the statements given below is correct?
a. In winter, the winds flow from the land to the ocean.
b. In summer, the winds flow from the land towards the ocean.
c. A cyclone is formed by a very high pressure system with very high speed winds revolving around it.
d. The coastline of India is not vulnerable to cyclones.
Answer:
The statements ‘a’ and ‘c’ are true. The statements ‘b’ and ‘d’ are not correct.

Reason for statement ‘a’:
During winter, the high pressurised cool air goes on to the surface of sea and low pressurised air with less density blows into the land.

Reason for statement ‘b’:
During summer, warmth air with less density and pressure goes up and down pressurised air blows from sea surface to the land.

Reason for statement ‘c’:
When the wind gets tremendous pressure, its speed of blowing also rises. Very high pressurised wind when it blows with high speed, it revolves around it.

Reason for statement ‘d’:
Our country’s coast line is highly vulnerable to the cyclones. Cyclones may hit any coastal region of India due to formation of severe low depressions.

Project Work

Read the following procedure and make your own anemometer.

Question 12.
Collect the following items and prepare the anemometer on your own.
a. 4 small paper cups
b. Two strips of the card board 20 cm long; 2 cm width.
c. Gum
d. Stapler
e. Sketch pen
f. Sharpened pencil.
Answer:
Aim : To make the anemometer with the collected items.

Procedure :

• Two strips of the cardboard are taken. Crosses are drawn on the strips as shown in the figure.
• The strips are fixed at the centre, putting one over the other, they make a ‘+‘ sign.
• Four small paper cups are fixed at the end of the strips. One of the fixed cups is coloured with sketch pen.
• It is seen that all four cups should face in the same direction.
• A pin is pushed through the centre of the strips and strips are attached to the sharpened pencil.
• The strips are checked that they rotate freely when we blow on the cups.
• The entire equipment is called anemometer

Working of anemometer : Number of rotations for a minute will give an estimated speed of the wind.

Question 13.
Collect some articles and photographs from news papers and magazines about storms and cyclones. Make a story on the basis of what you learnt in this chapter.
Answer:
The above collected pictures of satellite images reveal how cyclones and depressions occur in the seas and oceans.

Formation of cycle:

• Our country is in tropical region.
• Tropical cyclones are like giant engines that use warm moist air as fuel.
• The warm air rises causing an area of lower air pressure below.
• Air from surrounding areas of high air pressure pushes into the low pressure areas. Then the ‘new’ air becomes warm and rises too.
• As the warm air continues to rise, the surrounding air swirls – in to take its place, the water from the sea surface also comes up with the air as we have seen in the pictures.
• As the warmed moist air rises and cools off, the water in the air forms clouds.
• The whole system of clouds and winds spins and grows, fed by the ocean’s heat and water evaporating from the surface.
• Satellite images help us to predict the path of the cyclones to some extent.

Question 14.
Interview eye witnesses to collect the actual experiences of people affected by a cyclone.
Answer:

• How did you feel when cyclone hit your area?
• What was the speed of winds during cyclone?
• Where did you stay during heavy cyclone?
• Is there any damage occured to your home?
• How have you saved you and your family from cyclone ?
• Did you seek any one’s help at that time?

Question 15.
More fun with air.
Do the following activities and write your findings.

A. Take an empty bottle and place it on the table as shown in figure. Place a cotton ball just inside its mouth. Now try to blow air on the ball to send it into the bottle, and then try the activity with bottles of different sizes. Throw a challenge to your friends whether they can send the cotton ball inside the bottle by blowing air. Are you surprised ? Why did this happen ? Think about it and discuss with your friends.

Answer:
The blowing air could not send the cotton ball inside the bottle because the air present in the bottle exists pressure towards outside of the bottle. The same results are seen in the activities done with bottles of different sizes.

B. Can you blow out the ball from funnel?
Take a funnel and ball, keep the funnel in your mouth as shown in figure. Keep the ball in the funnel. Blow air through the funnel and try to send out the ball from funnel. What happens ? Have you succeeded in sending the ball out?

And then place the ball on your hand and put the funnel over the ball as shown in figure. Now blow air forcefully through funnel and try to blow out the ball from the funnel (while blowing air, remove hand.)

• What did you observe?
• What did you expect?
• What happens?

Try to answer and discuss with your friends.
Answer:

• When we blow air through the funnel, the ball jumps but does not fall from it.
• It is because blowing air is some what less denser and the air above the funnel exerts downward pressure.
• That influences the ball to jump over funnel.
• Hence we may not succeed in sending the ball out of the funnel.
• The second picture also tells us that the ball has not fallen because the size of the ball and radius of the funnel tube is same. We expect that the ball would fall from the funnel.
• Moreover, the air below the funnel exerts upward pressure.

C) Flow of air.
Take a large plastic bottle and a two holed rubber cork that fits firmly into its mouth. Also take two glass tubes. Tie a coloured balloon to the lower end of one of the glass tubes. Insert the glass tubes into the two holes of the cork. The glass tubes should fit tightly in the holes. Close the mouth of the bottle with the cork and seal it with sealing wax to make the bottle airtight. The balloon should be inside the bottle as shown in fig.
Now suck air out of the bottle through the tube that doesn’t have a balloon attached to it.

• What happens to the balloon?
• Why do you think this happened?

Answer:

• When we suck air out of the bottle through the tube, the balloon starts bulging itself.
• When the air is sucked out of the bottle, the pressure inside the bottle decreases.
• At that time, air from outside exerts downward pressure on the glass tube which is fixed with balloon.
• Downward pressure of the air enters the tube and fills the balloon to some extent.
• Then the balloon swells with high pressure which is more than that of air free bottle.

TS 7th Class Science 8th Lesson Notes Air, Winds and Cyclones

• Wind : The air around us is rarely still. It moves continuosly from one direction to another. The movement is in many directions. We call it wind.
• Expansion : Air expands on heating and contracts on cooling.
• Anemometer : The instrument used to measure the speed of air.
• Cyclone : An extremely large, powerful and destructive storm with very high winds that turn around an area of low
  pressure.
• low pressure : Decrease in pressure of air in a specific area causes low pressure.
• High pressure : The pressure increases in a specific area.
• Air around us exerts pressure.
• Warm air rises up whereas compara ti ve! y cooler air tends to sink towards the earth surface.
• As warm air rises up, pressure at the place is reduced and the cooler air noves into that place.
• Uneven heating on the earth causes wind movements.
• It has become easier to study cyclones with the help of advanced technology like satellites and radars.