NCERT Solutions for Class 8 Science Curiosity Chapter 6 Pressure, Winds, Storms and Cyclones

1. Choose the correct statement.
(i) Look at Fig. 6.21 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
See AnswerThe correct answer is (d) equal in all three vessels. This is because of a wonderful property of liquids: they always find their own level. In connected containers, no matter their shape or size, the liquid will settle at the same height in all of them.

(ii) A rubber sucker (M) is pressed on a flat 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.
See AnswerThe correct answer is (c) M will stick but N will not stick. A sucker works because it pushes air out, letting the higher atmospheric pressure outside hold it in place. This requires an airtight seal, which can only be formed on a smooth surface. A rough surface allows air to leak back in, equalizing the pressure and preventing the sucker from sticking.

(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.
See AnswerThe correct answer is (a) increase the height ‘H’ at which the tank is placed. The pressure exerted by a liquid depends on the height of the liquid column above the point of measurement. The higher the tank, the taller the water column and the greater the pressure at the taps below.

(iv) Two vessels, A and B contain water up to the same level as shown in Fig. 6.22. Pₐ and Pₑ is the pressure at the bottom of the vessels. Fₐ and Fₑ is the force exerted by the water at the bottom of the vessels A and B.
(a) Pₐ = Pₑ, Fₐ = Fₑ
(b) Pₐ = Pₑ, Fₐ < Fₑ
(c) Pₐ < Pₑ, Fₐ = Fₑ (d) Pₐ > Pₑ, Fₐ > Fₑ
See AnswerThe correct answer is (b) Pₐ = Pₑ, Fₐ < Fₑ. Pressure at the bottom (P) only depends on the height of the water, and since the heights are the same, Pₐ = Pₑ. However, force (F) is calculated as Pressure × Area. Since vessel B has a larger base area than vessel A, it will experience a greater total force, even though the pressure is the same. Thus, Fₐ < Fₑ.

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. [ ]
See Answer[T] True. This is the fundamental rule that creates winds! Nature always tries to balance things out, so air rushes from crowded high-pressure areas to less crowded low-pressure areas.

(ii) Liquids exert pressure only at the bottom of a container. [ ]
See Answer[F] False. Liquids are very generous with their pressure! They exert it not just on the bottom, but also on the sides of their container, and in fact, in all directions.

(iii) Weather is stormy at the eye of a cyclone. [ ]
See Answer[F] False. The eye of a cyclone is famously calm. The most violent and stormy part of a cyclone is the ‘eyewall’ that surrounds the calm center.

(iv) During a thunderstorm, it is safer to be in a car. [ ]
See Answer[T] True. A metal car acts like a protective shield called a Faraday cage. If lightning strikes, the electricity flows over the outer metal body of the car and into the ground, keeping the people inside safe.

3. Fig. 6.23a shows a boy lying horizontally, and Fig. 6.23b shows the boy standing vertically on a loose sand bed. In which case does the boy sink more in sand? Give reasons.
See AnswerThe boy will sink more when he is standing vertically (Fig. 6.23b). The reason is all about pressure! Pressure is defined as Force divided by Area. In both cases, the force is the same (the boy’s weight). However, when he is standing, his entire weight is concentrated on the small area of his feet. This small area results in high pressure, pushing the sand away and causing him to sink. When he is lying down, the same weight is spread out over a much larger area, resulting in low pressure, so he won’t sink much.

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.
See AnswerFirst, we find the total area the elephant is standing on.
Area of one foot = 0.25 m²
Total Area (A) = 4 feet × 0.25 m²/foot = 1.0 m²
Now, we calculate the pressure.
Force (F) = Elephant’s weight = 20000 N
Pressure (P) = Force / Area
P = 20000 N / 1.0 m² = 20000 N/m²
So, the pressure exerted by the elephant is 20,000 Pascals (Pa).

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 N, find out which boat will experience more pressure on its base and by how much?
See AnswerFor Boat A:
Total Force (Fₐ) = 5 persons × 700 N/person = 3500 N
Area (Aₐ) = 7 m²
Pressure (Pₐ) = Fₐ / Aₐ = 3500 N / 7 m² = 500 N/m²
For Boat B:
Total Force (Fₑ) = 3 persons × 700 N/person = 2100 N
Area (Aₑ) = 3.5 m²
Pressure (Pₑ)
= Fₑ/Aₑ
= 2100 N/3.5 m²
= 600 N/m²
So, the boat B will experience more pressure on its base.
Difference in pressure
= Pₑ – Pₐ
= 600 N/m² – 500 N/m²
= 100 N/m².

6. Would lightning occur if air and clouds were good conductors of electricity? Give reasons for your answer.
See AnswerNo, lightning would not occur. Lightning is a dramatic, sudden discharge of electricity that happens precisely because air is a poor conductor (an insulator). This allows a massive amount of static electric charge to build up in the clouds. If clouds and air were good conductors, this charge would continuously and gently leak away, never building up to the huge potential needed for a powerful lightning strike.

7. What will happen to the two identical balloons A and B as shown in Fig. 6.24 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.
See AnswerYes, both balloons will bulge, and they will bulge equally. The pressure in a liquid increases with depth. Since the two outlets for the balloons are at the same height from the bottom of the bottle, the water pressure at both outlets will be identical. This equal pressure will push into both balloons with the same force, causing them to inflate to the same extent.

8. Explain how a storm becomes a cyclone.
See AnswerA storm transforms into a mighty cyclone through a specific recipe of ingredients, usually found over warm ocean waters. Here’s the process:
1. Warm, moist air above the ocean gets heated and rises, creating a region of low pressure.
2. Cooler air from the surroundings rushes in to fill this low-pressure area.
3. As the warm air rises higher, the water vapor in it cools and condenses, releasing a lot of heat. This heat warms the air even more, making it rise faster and creating an even stronger low-pressure center.
4. This sets up a continuous cycle. The final ingredient is the Earth’s rotation, which causes this whole system of rushing winds and clouds to start spinning, organizing it into the characteristic swirling pattern of a cyclone.

9. Fig. 6.25 shows trees along the sea coast in a summer afternoon. Identify which side is land – A or B. Explain your answer.
See AnswerSide B is the land, and side A is the sea. During a summer afternoon, the land heats up much faster than the sea. The air above the hot land becomes warm and rises, creating an area of low pressure. The air above the cooler sea remains at a higher pressure. As we know, wind blows from high pressure to low pressure, so a cool ‘sea breeze’ blows from the sea (A) towards the land (B). The picture shows the trees bending in the direction of the wind, from A to B.

10. Describe an activity to show that air flows from a region of high pressure to a region of low pressure.
See Answer1. Take one balloon and attach a drinking straw to its opening.
2. Inflate a second balloon fully, but don’t tie it. This balloon is now a high-pressure region.
3. Carefully attach the free end of the straw to the opening of the inflated balloon.
4. Now, let go. You will observe that air rushes from the inflated (high-pressure) balloon, through the straw, and into the uninflated (low-pressure) balloon, causing the first balloon to shrink and the second one to inflate. This continues until the pressure in both balloons is nearly equal. This clearly demonstrates that air moves from high pressure to low pressure.

11. What is a thunderstorm? Explain the process of its formation.
See AnswerA thunderstorm is a type of storm that produces lightning and its resulting sound, thunder. They are formed by a process of rapid air movement and charge separation.
1. It begins when warm, moist air near the ground rises quickly. This is called an updraft.
2. As this air rises into cooler parts of the atmosphere, the moisture condenses to form towering cumulonimbus clouds.
3. Inside these clouds, strong updrafts and downdrafts cause water droplets and tiny ice crystals to collide and rub against each other.
4. This rubbing action separates electric charges, just like rubbing a balloon on your hair.
5. When the charge separation becomes large enough, it discharges as a bolt of lightning, which rapidly heats the air and creates the sound of thunder.

12. Explain the process that causes lightning.
See AnswerLightning is a giant spark of static electricity in the atmosphere. It’s caused by the buildup of electric charges inside storm clouds.
1. Inside a tall thunderstorm cloud, strong air currents make water droplets and ice particles bump into each other.
2. This friction strips away electrons, causing a separation of charges. Typically, the lighter, positively charged ice crystals are carried to the top of the cloud, while the heavier, negatively charged water droplets sink to the bottom.
3. This creates a huge electrical potential difference. When this difference becomes too large for the air to insulate, a massive electrical discharge occurs. This bright flash is what we see as lightning. It can happen within the cloud, between two clouds, or between the bottom of the cloud and the positively charged ground.

13. Explain why holes are made in banners and hoardings.
See AnswerThis is a very clever application of pressure principles! Large banners and hoardings act like giant sails. When a strong wind blows, it exerts a massive amount of force on their large surface area. This force creates a high pressure that could easily tear the banner or even knock over the entire structure. By cutting holes or slits in the banner, you allow air to pass through it. This reduces the pressure difference between the front and the back of the banner, significantly lowering the total force exerted by the wind and preventing it from being damaged.