Pressure Winds Storms and Cyclones Class 8 Question Answer Science Chapter 6

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Class 8 Science Curiosity Chapter 6 Question Answer

Class 8 Science Ch 6 Pressure Winds Storms and Cyclones Question Answer

Class 8 Science Chapter 6 Pressure Winds Storms and Cyclones Question Answer (InText)

Question 1.
Do liquids also exert pressure? (Page 83)
Answer:
Yes, liquids exert pressure on the walls and bottom of the container they are stored in. This pressure increases with depth and acts in all directions.

Question 2.
What will happen to the bulge of the balloon, if we increase the height of the water column? (Page 84)
Answer:
If we increase the height of the water column, the bulge of the balloon will also increase. This happens because the pressure at the bottom becomes greater as the water column gets taller.

Question 3.
Does the difference in air pressure have anything to do with the formation of winds? (Page 88)
Answer:
Yes, winds are formed due to differences in air pressure; air moves from high pressure areas to low pressure areas, creating wind.

Question 4.
How do winds form? (Page 88)
Answer:
Winds form when air moves from a region of high pressure to a region of low pressure, usually due to uneven heating of the Earth’s surface.

Pressure Winds Storms and Cyclones Class 8 Questions and Answers (Exercise)

Question 1.
Choose the correct statement
(i) Look at figiire carefully. Vessel R is filled with water. When pouring of water is stopped, the level of water will be …………………..

(a) the highest in vessel P
(b) the highest in vessel Q
(c) the highest in vessel R
(d) equal in all three vessels

(ii) A rubber sucker (M) is pressed on a smooth surface and an identical sucker (N) is pressed on a rough surface.
(a) Both M and N will stick to their surfaces
(b) Both M and N will not stick to their surfaces.
(c) M will stick but N will not stick.
(d) M will not stick but N will stick.

(iii) A water tank is placed on the roof of a building at a height H. To get water with more pressure on the ground floor one has to
(a) increase the height H at which the tank is placed.
(b) decrease the height H at which the tank is placed.
(c) replace the tank with another tank of the same height that can hold more water.
(d) replace the tank with another tank of the same height that can hold less water.

(iv) Two vessels, A and Bcontain water up to the same level as shown in figure. p_A and p_B are the pressure at the bottom of the vessels F_A and F_B are the force exerted by the water at the bottom of the vessels A and B.

(a) P_A = P_B > F_A = F_B
(b) P_a = P_b – F_A < F_B
(c) P_A < P_B, f_A = f_B
(d) P_A > P_B > F_A >F_B
Answer:
(i) (d) Equal in all three vessels because pressure depends on the height of water column, not the shape.
(ii) (c) M will stick but N will not stick because smooth surface allows the air to be pushed out, creating a vacuum that helps it stick.
(iii) (a) Increase the height H at which the tank is placed Because pressure increases with the height of the water column.
(iv) (a) P_A = P_B, F_A = F_B because same height = same pressure = same force (if base area is same).

Question 2.
State whether the following statements are true (T) or false (F)
(i) Air flows from a region of higher pressure to a region of lower pressure.
(ii) Liquid exert pressure only at the bottom of a container.
(iii) Weather is stormy at the eye of a cyclone.
(iv) During a thunderstorm, it is safer to be in a car.
Answer:
(i) true
(ii) false
(iii) false
(iv) true

Question 3.
Fig. (a) below shows a boy lying horizontally and Fig (b) shows the boy standing vertically on a loose sand bed. In which case does the boy sink more in sand ? Give reason.

Answer:
The boy sinks more when standing vertically in Fig. (b). Because the pressure is more when force is applied on a smaller area (feet), unlike lying position where weight is spread over a larger area.

Question 4.
An elephant stands on four feet. If the area covered by one foot is 0.25 m², calculate the pressure exerted by the elephant on the ground if its weight is 20000 N.
Answer:
Given
Weight = 20000 N
Area per foot = 0.25 m²
Total area = 4 feet = 4 × 0.25 = 1 m²
Pressure = Force / Area = 20000 N / 1 m² = 20000 Pa

Question 5.
There are two boats, A and B. Boat A has a base area of 7 m² and 5 persons are seated in it. Boat B has a base area of 3.5 m² and 3 persons are seating in it. If each person has a weight of 700 Nm, then find out which boat will experience more pressure on its base and by how much?
Answer:
Pressure on base of boat A
Area = 7 m²
Total weight = 5 × 700 = 3500 N
Pressure = Force / Area = 3500 ÷ 7 = 500 Pa

Pressure on base of boat B
Area = 3.5 m²
Total weight = 3 × 700 = 2100 N
Pressure = 2100 ÷ 3.5 = 600 Pa
∴ Boat B experiences more pressure.
Difference = 600 Pa – 500 Pa = 100 Pa

Question 6.
Would lightning occur if air and clouds were good conductors of electricity? Give reason for your answer.
Answer:
No, lightning would not have occured if air and clouds were good conductors. This is because lightning is the result of electric charge build-up due to poor conductivity. If air and clouds were good conductors, charges would flow easily and not accumulate to cause lightning.

Question 7.
What would happen to the two identical balloons A and Bas shown in figure when water is filled into the bottle up to a certain height. Will both the balloons bulge? If yes, will they bulge equally? Explain your answer.

Answer:
Yes, both balloons will bulge, and they will bulge equally if the water level above them is the same. This is because pressure in a liquid depends only on the height of the water column, not on the shape or volume of the container.

Question 8.
Explain how a storm becomes a cyclone.
Answer:
A storm becomes a cyclone when warm, moist air rises rapidly and causes a strong low-pressure area above warm ocean. Cooler air from the surroundings rushes in, creating a spinning system of clouds and wind. Continuous supply of warm moist air makes the storm stronger, finally forming a cyclone.

Question 9.
Figure below shows trees along the sea coast in a summer afternoon. Identify which side is land A or B Explain your answer.

Answer:
Side A is land. During a summer afternoon, the land heats up faster than water, creating low pressure over land. Cool air from the sea (side B) blows toward the land, forming a sea breeze. The trees bend towards land, indicating wind is coming from the sea.

Question 10.
Describe an activity to show that air flows from a region of high pressure to a region of low pressure.
Answer:
Take two inflated balloons and hang them a few centimeters apart. Now blow air forcefully between them. You’ll see that the balloons move towards each other. This happens because blowing air creates a low pressure region between them, and the surrounding higher pressure air pushes the balloons inward. This shows that air flows from high pressure to low pressure.

Question 11.
What is thunderstorm? Explain the process of its formation.
Answer:
A thunderstorm is a weather condition with strong winds, thunder, lightning, and rain. It forms when the ground heats up quickly and warms the air above it.

This warm, moist air rises and cools at higher altitudes, forming large clouds. The rising air creates strong upward and downward winds, leading to thunder and lightning.

Question 12.
Explain the process that causes lightning.
Answer:
Inside the thundercloud, water droplets and ice particles rub against each other due to strong winds, creating electric charges. The upper part of the cloud becomes positively charged, and the lower part becomes negatively charged. When the charge difference becomes very large, the cloud discharges electricity, causing lightning either within clouds or between the cloud and the ground.

Question 13.
Explain why holes are made in banners and hoardings.
Answer:
Holes are made in banners and hoardings so that air can pass through them easily. This reduces air pressure acting on them and prevents the banners from tearing or flying away during strong winds.

Class 8 Science Chapter 6 Question Answer (Activities)

Activity 1 (Page 83)

Aim
To show that pressure exerted by a liquid depends on the height (depth) of the liquid column and not on the shape or volume of the container.

Materials Required
Two transparent plastic or glass pipes (same length but different diameters), two rubber balloons, water, and a stand with clamps.

Procedure

1. Take two transparent pipes of equal length (about 25 cm), but with different diameters as shown in fig a.
   
2. Attach a good quality rubber balloon to one end of each pipe.
3. Fix both pipes vertically on a stand using clamps as shown in fig a.
4. Pour water into both pipes until the water level in each pipe is exactly the same—about halfway up.
5. Observe the balloons carefully.

Observation
Both balloons bulge equally, even though the volume (and weight) of water in the wider pipe is more.

Conclusion
The pressure exerted by a liquid depends only on the height of the liquid column, not on the shape or amount of liquid in the container.

Viva Questions

1. What does this activity prove about liquid pressure?
2. If the water level is higher in one pipe, how will it affect the balloon bulge?

Activity 2 (Page 84)

Aim
To show that liquids exert pressure not just at the bottom but also on the sides of a container.

Materials Required
A used plastic bottle, water, tape, and a needle or nail.

Procedure

1. Take a clean plastic bottle and remove its cap.
2. Using a heated needle or nail, make four small holes near the bottom sides of the bottle at the same height as shown in fig (b).
   
3. Seal all the holes with tape.
4. Fill the bottle completely with water.
5. Now, remove all the tapes at the same time and observe.

Observation
Water flows out from all holes equally, and the streams move outwards like small fountains.

Conclusion
This proves that water exerts pressure on the sides of the container as well not just at the bottom. In fact, liquids exert pressure in all directions. That is why water leaks out with force from holes in water pipes.

Viva Questions

1. Why are all the holes made at the same height in this activity?
2. What everyday example shows that liquids exert pressure on pipe walls?

Activity 3 (Pages 85 and 86)

Aim
To show that air exerts pressure from above and presses against surfaces like paper.

Materials Required
Paper plate, stick, two identical chart paper sheets (about 70 cm × 56 cm), tape and scissors.

Procedure

1. Invert a paper plate and attach a stick upright at its centre as shown in fig (c).
   
2. Fold one chart paper twice and make a hole in the centre for the stick to pass through.
   
3. Place the folded chart paper over the plate with the stick passing through the hole as shown in fig (d). Try lifting the plate using the stick and observe the effort needed.
   
4. Now take the second chart paper (unfolded), make a centre hole, and place it flat cover the plate with the stick through the hole as shown in fig (e).
5. Try lifting the plate again and note the difference in effort.

Observation
It is harder to lift the plate when covered with the unfolded (flat) chart paper.

Conclusion
This shows that air presses down on surfaces. Since, the unfolded paper covers more area, air pressure on it is more, making it harder to lift. Thus, air exerts pressure from above and on all surfaces.

Viva Questions

1. Why was the plate harder to lift when using the unfolded chart paper?
2. What does this activity prove about the nature of air pressure?

Activity 4 (Page 87)

Aim
To observe how air pressure helps a rubber sucker stick to a surface.

Materials Required
A good quality rubber sucker and a smooth, flat surface (like a tile or table).

Procedure

1. Take the rubber sucker and press it firmly against a smooth, flat surface as shown in fig (f).
   
2. Let go and observe—it sticks to the surface.
3. Now, try pulling the sucker off the surface.

Observation
The sucker sticks tightly and is difficult to pull off.

Conclusion
When we press the sucker, most of the air between it and the surface gets pushed out. This creates a low pressure inside the sucker. The higher air pressure outside the sucker pushes it against the surface, making it stick. To pull it off, we must apply enough force to overcome the pressure difference. This shows that air pressure acts in all directions.

Note
Atmospheric pressure is very high—over a 15 cm × 15 cm area, it equals the weight of a 225 kg object! We don’t feel it because the pressure inside our body balances the outside pressure.

Viva Questions

1. Why does the sucker stick to the surface?
2. Why are we not crushed under the large atmospheric pressure?

Activity 5 (Page 88)

Aim
To show that air flows from a region of high pressure to low pressure.

Materials Required
Two similar thin rubber balloons, a drinking straw, rubber bands or thread.

Procedure

1. Insert one end of a straw into the neck of an empty balloon and tie it tightly using a rubber band or thread.
   
2. Inflate the second balloon and hold its mouth with your fingers to prevent air from escaping.
3. Insert the free end of the straw into the neck of the inflated balloon and secure it tightly.
4. Now release the mouth of the inflated balloon and observe both balloons as shown in fig (g).

Observation
Air flows from the inflated balloon to the empty balloon, making the empty balloon start inflating, while the inflated one deflates slightly.

Conclusion
This activity shows that air always moves from high pressure (more air) to low pressure (less air). The inflated balloon had higher air pressure, which pushed the air into the empty one.

Viva Questions

1. Why did the empty balloon inflate without blowing into it?
2. What does this activity tell us about the direction of air pressure flow?

Activity 6 (Page 89)

Aim
To observe how high-speed wind reduces air pressure and affects nearby objects.

Materials Required
Two same-sized balloons, string/thread, a stick or hanger.

Procedure

1. Inflate both balloons and tie a string to each.
   
2. Hang them from a stick or hanger so they hang side by side with a small gap of 6 – 10 cm between them as shown in fig (h).
3. Now blow air between the balloons and observe.
4. Blow harder and observe again.

Observation
As you blow between the balloons, they move towards each other. Blowing harder makes them come closer faster.

Conclusion
When we blow between the balloons, the air pressure in between reduces due to high-speed wind. The higher pressure on the outer sides pushes the balloons inward. This shows that high-speed wind is always accompanied by low air pressure.

Viva Questions

1. What caused the balloons to move towards each other?
2. What is the relationship between wind speed and air pressure?