Case Based Questions: Pressure, Winds, Storms, and Cyclones | Science Curiosity Class 8 - New NCERT PDF Download

Case Study 1

Ananya and her friends were flying kites on a windy afternoon. They noticed that on some days, the kites flew higher and the strings tugged harder. Ananya’s kite string broke when a sudden strong gust of wind blew. While walking home, she saw leaves swirling upward and dust moving along the ground. At home, she tried pushing a nail into a wooden board with its flat head and then with its pointed end, finding it easier with the pointed end. Ananya wondered why the wind was stronger on some days, how it lifted leaves, and why the nail was easier to push with its pointed end.

Questions

1. Why is it easier to push a nail into wood using its pointed end compared to its flat head? (2 marks)
Solution: It is easier to push a nail with its pointed end because pressure is force per unit area. The pointed end has a smaller area, so the same force creates higher pressure, making it easier to penetrate the wood.

2. What causes the wind to blow stronger on some days than others? (2 marks)
Solution: Wind blows stronger when there is a larger difference in air pressure between two regions. Air moves faster from high-pressure to low-pressure areas, creating stronger winds on some days.

3. How does the wind exert a force to lift leaves and move dust, and what type of pressure is involved? (3 marks)
Solution: Wind exerts a force by creating air pressure differences. When wind blows, it forms a low-pressure area where air moves quickly, lifting light objects like leaves and dust. This is due to atmospheric pressure, which pushes objects from high-pressure to low-pressure regions. The swirling motion happens as air rushes to fill low-pressure areas, carrying leaves upward.

4. Why did Ananya’s kite string break during a strong gust of wind? (2 marks)
Solution: The strong gust created high wind pressure, exerting a large force on the kite and string. The force was too strong for the string, causing it to break.

5. How does the concept of pressure explain why water tanks are placed at a height? (2 marks)
Solution: Water tanks are placed at a height to increase the pressure of water in pipes. Higher water columns exert more pressure at the bottom, ensuring a stronger water flow from taps.

Case Study 2

During a school experiment, Rohan and his classmates observed water spurting out from holes made at the same height on a plastic bottle’s sides. They noticed the water streams were equal in length. Later, Rohan saw a street vendor using a heavy stone with a broad base to hold down a cloth sheet against the wind. At home, he tried lifting a paper plate covered with a large chart paper and found it harder than lifting one with a folded, smaller chart paper. Rohan wondered why the water streams were equal, why the broad stone worked better, and why the paper plate was harder to lift with the larger paper.

Questions

1. Why did the water streams from the holes in the bottle come out equally? (2 marks)
Solution: The water streams were equal because the holes were at the same height. Liquid pressure depends on the height of the water column, so equal heights produce equal pressure, pushing water out the same distance.

2. Why did the street vendor use a heavy stone with a broad base to hold the cloth sheet? (2 marks)
Solution: The broad base of the stone spreads its weight over a larger area, reducing pressure on the cloth. This prevents the cloth from tearing and holds it firmly against the wind’s force.

3. Why was it harder for Rohan to lift the paper plate covered with a larger chart paper compared to a smaller, folded one? (3 marks)
Solution:
Lifting the paper plate with a larger chart paper was harder because air exerts atmospheric pressure on the paper’s surface. A larger area experiences more total force from the air pushing down, making it harder to lift. The smaller, folded paper has less area, so the air’s force is less, making lifting easier. This shows that atmospheric pressure acts on all surfaces, increasing with area.

4. How does liquid pressure differ from atmospheric pressure in this case? (2 marks)
Solution:
Liquid pressure, like in the bottle, depends on the height of the water column and acts in all directions. Atmospheric pressure, acting on the paper plate, is due to the weight of air and pushes on all surfaces equally, regardless of height.

5. What happens to the pressure at the bottom of a water tank if its height is increased? (2 marks)
Solution: If the water tank’s height is increased, the pressure at the bottom increases because liquid pressure depends on the height of the water column. A taller column exerts more pressure.

Case Study 3

During a stormy day, Priya noticed trees bending heavily due to strong winds. Her teacher explained that storms form when warm air rises, creating low pressure. Priya saw lightning and heard thunder, which scared her. She learned that her school building has a lightning conductor. Later, she conducted an experiment with two balloons tied to a stick, blowing air between them and observing them move closer. Priya wondered why storms form, how lightning occurs, and why the balloons behaved that way.

Questions

1. Why do trees bend during strong winds in a storm? (2 marks)
Solution: Trees bend because strong winds exert a force due to high air pressure differences. The wind’s force pushes against the trees, causing them to sway or bend.

2. What is the role of a lightning conductor in Priya’s school building? (2 marks)
Solution: A lightning conductor provides a safe path for electric charges from lightning to flow into the ground, protecting the building from damage or fire caused by lightning strikes.

3. How does warm air rising lead to the formation of a storm, and what role does moisture play? (3 marks)
Solution: Warm air rises because it is lighter, creating a low-pressure area. Cooler air rushes in, gets heated, and rises, forming a cycle. Moisture in the warm air condenses into water droplets, forming clouds. These droplets merge, causing rain and strong winds, which create a storm. Moisture is essential as it fuels cloud formation and rainfall.

4. Why did the balloons move closer when Priya blew air between them? (2 marks)
Solution: Blowing air between the balloons creates a low-pressure area because high-speed air reduces pressure. The higher atmospheric pressure around the balloons pushes them closer together.

5. Why do cyclones weaken when they move over land? (2 marks)
Solution: Cyclones weaken over land because they lose their source of warm, moist air from the ocean. Without moisture to fuel cloud formation and heat release, the cyclone’s winds and pressure differences decrease.

Case Study 4

Vikram lives in a coastal area prone to cyclones. During a weather forecast, he heard that a cyclone was approaching with winds up to 200 km/h. His family prepared an emergency kit and moved to a cyclone shelter. Vikram noticed that banners in his town had holes cut into them. At school, he learned that cyclones form over warm oceans and that Earth’s rotation affects their spin. Vikram wondered how cyclones form, why banners have holes, and whether cyclones would form if Earth stopped rotating.

Questions

1. Why do cyclones form over warm ocean waters? (2 marks)
Solution: Cyclones form over warm ocean waters because warm water heats the air above, making it rise and create a low-pressure area. This starts a cycle of rising air, cloud formation, and spinning winds.

2. Why do banners in Vikram’s town have holes cut into them? (2 marks)
Solution: Holes in banners allow wind to pass through, reducing air pressure differences across the banner. This lowers the force on the banner, preventing it from tearing during strong cyclone winds.

3. How does Earth’s rotation affect cyclone formation, and would cyclones form if Earth stopped rotating? (3 marks)
Solution: Earth’s rotation causes the Coriolis effect, which makes moving air spin, forming the rotating structure of cyclones. Warm, moist air rises over oceans, creating low pressure, and Earth’s rotation spins the winds into a cyclone. If Earth stopped rotating, the Coriolis effect would disappear, so cyclones wouldn’t form with their typical spinning pattern, though other storms might still occur.

4. Why did Vikram’s family move to a cyclone shelter? (2 marks)
Solution: Vikram’s family moved to a cyclone shelter to stay safe from the cyclone’s strong winds, heavy rain, and flooding, which can damage homes and endanger lives.

5. How does the India Meteorological Department (IMD) help during cyclones? (2 marks)
Solution: The IMD monitors cyclones using satellites, predicts their paths, and issues warnings. This helps people prepare, evacuate, or take safety measures to reduce damage and save lives.