NCERT Solutions Class 8 Science Chapter 06 Pressure, Winds, Storms and Cyclones

Question 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
Answer: (d) equal in all three vessels
This result occurs due to a special characteristic of liquids - they consistently reach their own level. In containers that are joined together, regardless of their individual shape or size, the liquid will settle at the same height throughout all of them.
In simple words: Water in connected containers always stays at the same height in each one, no matter what shape the containers are.

Exam Tip: Remember that connected containers always have water at equal heights - this is a key principle tested in pressure questions. Draw the three vessels to visualize this property.

Question 1. (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
Answer: (c) M will stick but N will not stick
A sucker functions by forcing air out, which permits the stronger atmospheric pressure from outside to hold it in position. This needs an airtight seal, achievable only on a smooth surface. A rough surface permits air to enter back in, making pressures equal and stopping the sucker from adhering.
In simple words: A sucker sticks to smooth surfaces because air gets trapped, but it cannot stick to rough surfaces because air leaks back in.

Exam Tip: Focus on the concept of airtight seals and pressure difference - this is what makes a sucker work or fail.

Question 1. (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
Answer: (a) increase the height 'H' at which the tank is placed
The pressure created by a liquid relies on how high the liquid column is above the point where you measure it. When the tank sits higher, the water column becomes taller and the pressure at the faucets below gets stronger.
In simple words: The higher the water tank, the more pressure the water has when it comes out of the taps below.

Exam Tip: Pressure in liquids depends only on depth or height, not on the amount of water - this is a frequently tested concept.

Question 1. (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
Answer: (b) Pₐ = Pₑ, Fₐ < Fₑ
Pressure at the bottom depends only on the height of the water, and since both vessels have water at the same height, the pressures are equal - Pₐ = Pₑ. Force, however, is found by multiplying Pressure by Area. Vessel B has a bigger base than vessel A, so it feels a greater total force even when the pressure is the same. Therefore, Fₐ < Fₑ.
In simple words: Equal heights mean equal pressure, but a wider vessel has more area, so the total pushing force is bigger.

Exam Tip: Distinguish between pressure (depends on height only) and force (pressure times area) - this difference is crucial for solving multi-part pressure problems.

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.
Answer: [T] True
This is the key rule that generates winds! Nature continuously seeks balance, so air moves from packed high-pressure zones toward less packed low-pressure zones.
In simple words: Air always wants to move from crowded, high-pressure places to empty, low-pressure places.

Exam Tip: This fundamental principle explains wind formation and is the basis for understanding cyclones and storms.

Question 2. (ii) Liquids exert pressure only at the bottom of a container.
Answer: [F] False
Liquids are generous with their pressure! They push not just on the bottom, but also on the sides of the container, and actually, in every direction at once.
In simple words: Liquids push on the bottom, the sides, and everywhere inside the container, all at the same time.

Exam Tip: Always remember that liquid pressure acts in all directions - this is why water leaks from every point if a container breaks.

Question 2. (iii) Weather is stormy at the eye of a cyclone.
Answer: [F] False
The eye of a cyclone is famously calm and peaceful. The most violent and intense part of a cyclone is the 'eyewall' - the ring of clouds and wind that surrounds this peaceful center.
In simple words: The middle of a cyclone is calm and quiet, but the ring around it is where the strongest winds and storms happen.

Exam Tip: The eye is the calmest part - students often get this backwards; remember that the eyewall surrounding the eye contains the worst weather.

Question 2. (iv) During a thunderstorm, it is safer to be in a car.
Answer: [T] True
A metal car works like a protective shield known as a Faraday cage. When lightning hits, the electric current travels over the outer metal body and down into the ground, keeping everyone inside protected from harm.
In simple words: A car's metal body protects you by letting electricity flow around the outside and into the ground, not through you.

Exam Tip: The Faraday cage principle - where a metal conductor protects the interior - is important for safety science and also tested in physics chapters.

Question 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.
Answer: The boy will sink deeper when standing vertically (Fig. 6.23b). The reason relates to pressure! Pressure gets calculated as Force divided by Area. In both positions, the force stays the same - it is the boy's weight. However, when standing, his entire weight lands on just the small area of his feet. This small area produces high pressure, pushing sand aside and making him sink. When lying down, that same weight spreads across a much bigger area, creating low pressure, so he stays mostly on top.
In simple words: Standing puts all your weight on a tiny spot (your feet), so you sink. Lying down spreads your weight over a big area, so you don't sink as much.

Exam Tip: Remember the pressure formula (Force/Area) and how a small area with the same force creates much higher pressure - this is why high heels sink into grass while flat shoes don't.

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: First, we find the total area the elephant stands on.
Area of one foot = 0.25 m²
Total Area (A) = 4 feet × 0.25 m²/foot = 1.0 m²

Now we work out the pressure.
Force (F) = Elephant's weight = 20000 N
Pressure (P) = Force / Area
P = 20000 N / 1.0 m² = 20000 N/m²

The pressure exerted by the elephant equals 20,000 Pascals (Pa).
In simple words: An elephant's weight spreads over four feet, which gives a big total area. When you divide its weight by this large area, the pressure turns out to be the same as if a human pushed down on the same space.

Exam Tip: Always multiply the single-foot area by the number of feet first - forgetting this step is a common mistake that leads to a pressure value four times too high.

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 N, find out which boat will experience more pressure on its base and by how much?
Answer: For 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

Boat B will face more pressure on its base.

Difference in pressure = Pₑ - Pₐ = 600 N/m² - 500 N/m² = 100 N/m²
In simple words: Even though Boat B has fewer people, its smaller base spreads their weight over less space, making the pressure higher than Boat A.

Exam Tip: Remember that pressure depends on both force AND area - more people with a larger area might have lower pressure than fewer people with a tiny area.

Question 6. Would lightning occur if air and clouds were good conductors of electricity? Give reasons for your answer.
Answer: No, lightning would not happen. Lightning is a sudden, powerful release of electricity that occurs precisely because air works poorly as a conductor (it is an insulator). This poor conductivity lets a huge amount of static electric charge gather in the clouds. If air and clouds were good conductors instead, this charge would slowly and gently drain away continuously, never building up to the massive potential difference needed to create a strong lightning strike.
In simple words: Lightning needs charge to build up. If air let electricity flow away easily, there would be no buildup and no lightning.

Exam Tip: The key concept is that insulators prevent charge loss (allowing buildup), while conductors let it escape - this is why lightning happens in air, not in metals.

Question 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.
Answer: Yes, both balloons will bulge, and they will bulge in equal measure. The pressure inside a liquid gets stronger as you go deeper. Since the two outlets for the balloons are positioned at the same distance from the bottom of the bottle, the water pressure pushing on both outlets will be identical. This matching pressure will push into both balloons with the same strength, making them inflate to the same size.
In simple words: Both balloons are at the same depth in the water, so they feel the same pressure and blow up equally.

Exam Tip: Pressure in a liquid only depends on depth - at the same height inside the bottle, all points have equal pressure, so connected balloons will inflate equally.

Question 8. Explain how a storm becomes a cyclone.
Answer: A storm grows into a powerful cyclone through a specific set of conditions, typically found over warm ocean waters. The process unfolds as follows:

1. Warm, moist air above the ocean gets heated and rises, forming a low-pressure zone.

2. Cooler air from nearby regions rushes in to fill this low-pressure space.

3. As the rising warm air moves higher, water vapor cools and changes into liquid, releasing significant heat. This heat warms the air further, making it rise even faster and creating an even stronger low-pressure center.

4. This starts a continuous loop. The final element is Earth's rotation, which spins this whole moving system of winds and clouds, organizing it into the classic rotating shape of a cyclone.
In simple words: Warm air rises, cooler air moves in, water releases heat, and Earth's spin twists it all into a spinning storm.

Exam Tip: Remember the three key ingredients - warm ocean water (heat source), air movement (updrafts and downdrafts), and Earth's rotation (Coriolis effect) - all are needed to form a cyclone.

Question 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.
Answer: Side A is the land and side B is the sea. In a summer afternoon, the land warms up much faster than the sea. The air above the hot land gets warm and rises, creating a low-pressure zone. The air above the cooler sea stays at a higher pressure. Since wind travels from high pressure toward low pressure, a cool 'sea breeze' blows from the sea (B) toward the land (A). The picture shows the trees leaning in the wind's direction, from B to A.
In simple words: Land heats up faster than water, so air rises above land, pulling cooler sea air toward it - that's why the trees bend toward the land.

Exam Tip: Sea and land breezes depend on temperature differences - always remember that land heats and cools faster than water, creating the pressure differences that drive these winds.

Question 10. Describe an activity to show that air flows from a region of high pressure to a region of low pressure.
Answer: 1. Take one balloon and tie a drinking straw to its opening.

2. Inflate a second balloon completely, but do not seal it. This balloon now represents a high-pressure zone.

3. Carefully connect the free end of the straw to the opening of the inflated balloon.

4. Now release them both. You will see that air rushes from the inflated (high-pressure) balloon, travels through the straw, and fills the empty (low-pressure) balloon, making the first balloon smaller and the second one bigger. This process continues until the pressure inside both balloons becomes roughly equal. This clearly shows that air moves from high pressure to low pressure.
In simple words: Connect two balloons with a straw - one full, one empty. Air will move from the full one to the empty one until they are equally full.

Exam Tip: This is a hands-on demonstration of pressure equalization - the visual proof that nature always tries to balance pressure differences by moving air from high to low pressure zones.

Question 11. What is a thunderstorm? Explain the process of its formation.
Answer: A thunderstorm is a storm type that generates lightning and thunder - the sound that follows the lightning flash. They develop through a process of fast air movement and separation of electrical charges.

1. The process starts when warm, moist air at ground level rises very quickly - this upward movement is called an updraft.

2. As this air moves up into colder parts of the atmosphere, the water vapor condenses, forming huge cumulonimbus clouds that tower high into the sky.

3. Inside these clouds, strong updrafts and downdrafts make water droplets and tiny ice crystals collide and rub against one another.

4. This friction separates electrical charges, similar to what happens when you rub a balloon on your hair.

5. When the separated charges become big enough, they release as a lightning bolt, which heats the air extremely fast and creates the loud sound we call thunder.
In simple words: Warm air rises fast, clouds form, ice and water bump together and build up charges, then suddenly release electricity as lightning and thunder.

Exam Tip: The key stages are updraft, condensation, collision (charge separation), and discharge - knowing these stages helps answer longer questions about thunderstorm formation.

Question 12. Explain the process that causes lightning.
Answer: Lightning is a massive electrical spark in the atmosphere caused by the buildup of electrical charges inside storm clouds.

1. Inside a towering thunderstorm cloud, strong air currents force water droplets and ice particles to collide and bump into one another repeatedly.

2. This friction removes electrons from the particles, separating electrical charges. Usually, the lighter, positively charged ice crystals get carried to the top of the cloud, while the heavier, negatively charged water droplets sink to the bottom.

3. This arrangement creates a huge electrical potential difference. When this difference becomes too strong for air to hold back, a massive electrical discharge happens. This bright flash is what we observe as lightning. It can travel within a single cloud, jump between two clouds, or strike from the bottom of a cloud to the positively charged ground.
In simple words: Particles in clouds bump together, electrons get separated, charges build up, and when the difference gets too big, electricity jumps as lightning.

Exam Tip: Understand the charge separation process (positive ions up, negative ions down) and how this creates the potential difference that discharges as lightning - this detailed understanding often scores extra marks.

Question 13. Explain why holes are made in banners and hoardings.
Answer: This is a clever use of pressure science! Large banners and hoardings function like giant sails. When strong wind blows on them, it applies a huge amount of force to the large surface. This force creates high pressure that could tear the banner or knock down the entire structure. By cutting holes or slits into the banner, air can travel through instead of pushing against it. This lets air pass through and reduces the pressure difference between the front and back surfaces, greatly decreasing the total force the wind applies and keeping the banner from breaking.
In simple words: Holes let wind pass through the banner instead of pushing against it, so the force gets much smaller and the banner stays safe.

Exam Tip: The key principle is reducing pressure difference - whenever wind or fluid pressure might damage a structure, engineers create openings to allow flow-through rather than blockage, which reduces the net force.