Keep the Curiosity Alive — Chapter Exercises — Pressure, Winds, Storms, and Cyclones

1. 15 marksCuriosity Grade 8, Chapter 6, pages 94-95, exercise 1

   Choose the correct statement.

   (i) In Fig. 6.21 three vessels P, Q and R are joined by tubes near their bases. Vessel R is filled with water. When pouring stops, the level of water will be — (a) highest in P, (b) highest in Q, (c) highest in R, (d) equal in all three vessels.

   (ii) A rubber sucker (M) is pressed on a flat smooth surface and an identical sucker (N) on a rough surface — (a) both stick, (b) neither sticks, (c) M sticks but N does not, (d) M does not stick but N does.

   (iii) A water tank is on a roof at height H. To get water at more pressure on the ground floor, one has to — (a) increase H, (b) decrease H, (c) use a tank of the same height holding more water, (d) use a tank of the same height holding less water.

   (iv) Two vessels A and B contain water to the same level (Fig. 6.22), B being the wider. P and F are the pressure and the force at the bottom — (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.

   Hint. Every part turns on the same fact: liquid pressure depends on the height of the column.

   (i) Answer: (d) equal in all three vessels.

   The three vessels are joined by tubes near their bases, so they form one connected body of water. Water flows between them until the pressure at the joins is the same, and since the pressure exerted by a liquid in a vessel depends on the height of its column, that happens when the heights are equal. The vessels have different shapes and widths, and it makes no difference — exactly as the two pipes of Activity 6.1 gave equal bulges despite different diameters.

   (ii) Answer: (c) M will stick but N will not stick.

   A sucker works by a pressure difference: pressing it out expels most of the air, the pressure of air surrounding the sucker is higher than the pressure exerted by the air inside, and the outside air holds it on. On a rough surface, air leaks back in through the gaps between the cup and the surface, the inside pressure rises to match the outside, the difference vanishes, and N falls off. This is why Activity 6.4 specifies a smooth flat surface.

   (iii) Answer: (a) increase the height 'H' at which the tank is placed.

   Pressure depends on the height of the water column above the tap, not on the amount of water. Options (c) and (d) change how much water the tank holds while keeping the same height — which changes nothing at all. Option (b) would make matters worse.

   (iv) Answer: (b) P_A = P_B, F_A < F_B.

   	Reasoning
   Pressure	Both vessels are filled to the same level, and pressure depends only on the height of the column. So P_A = P_B
   Force	Force = pressure × area. The pressures are equal, but B has the larger base, so F_B > F_A, that is F_A < F_B

   ✦ Part (iv) is the one that separates students who have understood from those who have memorised. It requires holding two ideas at once: equal pressures and unequal forces, in the same pair of vessels. If you remember only 'pressure depends on height' you will pick (a); if you remember only 'more water pushes harder' you will pick (d). The formula Pressure = Force ÷ Area, rearranged as Force = Pressure × Area, gives both answers at once.

2. 24 marksCuriosity Grade 8, Chapter 6, page 95, exercise 2

   State whether True [T] or False [F].

   (i) Air flows from a region of higher pressure to a region of lower pressure.

   (ii) Liquids 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.

   Hint. Each is settled by a single sentence of the chapter.

   (i) True. This is the conclusion of Activity 6.5: air moves from a region of high air pressure to a region of low air pressure. It is what makes a wind a wind, and it explains the deflating balloon, the punctured bicycle tube, and every breeze in the chapter.

   (ii) False. Activity 6.2 settles it: water flows out through holes made in the sides of a bottle. Liquids exert pressure not only at the bottom of the container, but also on its sides. In fact liquids exert pressure in all directions. The word only is what makes the statement wrong.

   (iii) False. The opposite is true. At the eye of the cyclone, the wind is calm, but the surrounding region experiences strong winds and heavy rainfall. The eye is the lowest-pressure point and the calmest place in the whole system.

   (iv) True. If you are inside a bus or a car, you are comparatively safer. Note the chapter's word comparatively — safer than standing in the open or under a tall tree, not absolutely safe.

   ✦ Two of these four are traps of the same kind. In (ii) the error is the word only, which turns a true statement into a false one, since liquids do press on the bottom — just not exclusively. In (iii) the error is a straightforward reversal of the fact. So when a True/False statement contains only, always or never, check that word first, because it is usually where the statement has been made false.

3. 34 marksCuriosity Grade 8, Chapter 6, page 95, exercise 3

   Fig. 6.23a shows a boy lying horizontally and Fig. 6.23b shows him standing vertically on a loose sand bed. In which case does he sink more into the sand? Give reasons.

   Hint. His weight is the same in both pictures. What is not?

   He sinks more when standing (Fig. 6.23b).

   The reasoning.

   	Lying down (a)	Standing (b)
   His weight	The same	The same
   Area in contact with the sand	Large — his whole body	Small — only the soles of his feet
   Pressure on the sand	Low	High
   How far he sinks	Less	More

   Since Pressure = Force ÷ Area and the force is unchanged, the smaller contact area when standing gives a much higher pressure on the sand — and loose sand gives way under high pressure.

   ✦ This is the schoolbag straps again, with the roles of body and load reversed. There a fixed weight pressed on a small or large area of the boy; here the boy's fixed weight presses on a small or large area of the sand. Same formula, same conclusion: spreading the same force over more area lowers the pressure.

   Why the sand has to be loose for the question to work. On a hard floor neither position leaves a mark, because the floor does not give way at either pressure. Loose sand is chosen because it responds visibly to the difference.

   The everyday version: this is exactly why someone crossing a patch of soft mud or thin ice is advised to lie down and spread out rather than walk across it.

4. 43 marksCuriosity Grade 8, Chapter 6, page 95, exercise 4

   An elephant stands on four feet. If the area covered by one foot is 0.25 m², calculate the pressure exerted on the ground if its weight is 20000 N.

   Hint. The elephant is standing on four feet, not one.

   Given:

   • Weight (the force pressing down) = 20000 N
   • Area of one foot = 0.25 m²
   • Number of feet on the ground = 4

   Step 1 — total area of contact.

   Total area = 4 × 0.25 m² = 1 m²

   Step 2 — pressure.

   Pressure = Force ÷ Area = 20000 N ÷ 1 m² = 20000 N/m²

   Answer: 20000 N/m², that is 20000 Pa.

   ✦ The whole question is Step 1, and it is where marks are lost. The elephant's weight is spread over all four feet, so the area to divide by is 1 m², not 0.25 m². Dividing by one foot's area gives 80000 Pa — four times too big — and it is the commonest wrong answer.

   A quick way to check you have it the right way round: if the elephant lifted one foot, it would be standing on less area, so the pressure would go up, not down. More feet on the ground means lower pressure — which is why the total area is the one to use.

   Always write the unit. A bare '20000' is not a pressure. And if your units come out as newton or metre² rather than N/m², you have divided the wrong way round.

5. 54 marksCuriosity Grade 8, Chapter 6, page 96, exercise 5

   Boat A has a base area of 7 m² and 5 persons seated in it. Boat B has a base area of 3.5 m² and 3 persons in it. If each person weighs 700 N, which boat experiences more pressure on its base, and by how much?

   Hint. Work out each boat's force first, then divide. Do not compare the numbers of people.

   Boat A

   Force = 5 × 700 N = 3500 N

   Pressure = 3500 N ÷ 7 m² = 500 N/m²

   Boat B

   Force = 3 × 700 N = 2100 N

   Pressure = 2100 N ÷ 3.5 m² = 600 N/m²

   Comparison

   	Boat A	Boat B
   Persons	5	3
   Force	3500 N	2100 N
   Base area	7 m²	3.5 m²
   Pressure	500 N/m²	600 N/m²

   Answer: Boat B experiences more pressure, by 600 − 500 = 100 N/m² (100 Pa).

   ✦ The point of the question is that the boat with fewer people and less total weight is under the greater pressure. Boat A carries a bigger load — 3500 N against 2100 N — and still ends up with the lower pressure, because its base is twice as large. Comparing the number of passengers, or the total weight, gives the wrong answer. Only force per unit area decides it.

   Do not stop at 'B experiences more pressure'. The question asks by how much, so the difference and its unit are part of the answer.

   An assumption worth stating: this uses only the passengers' weight. The weight of the boats themselves is not given, so it is left out — say so in your answer rather than inventing a figure.

6. 64 marksCuriosity Grade 8, Chapter 6, page 96, exercise 6

   Would lightning occur if air and clouds were good conductors of electricity? Give reasons for your answer.

   Hint. The insulating air is not in the way of lightning — it is part of how lightning works.

   No, lightning as we know it would not occur.

   The reason lies in what the insulating air is doing now. Normally, air acts as an electrical insulator and does not let opposite charges meet. But when the build up of charges becomes very large, the insulating property of air breaks down. A sudden flow of charges takes place, producing a bright flash of light called lightning.

   So insulating air is a necessary ingredient, not an obstacle. It is what allows charge to accumulate to an enormous level before anything is released.

   If air were a good conductor. Charge would leak away continuously, as fast as the rubbing of ice particles and water droplets produced it. No large build-up would ever form, so there would be no breakdown and no sudden discharge — no bright flash, and no thunder either, since thunder is the sound of air heated by the flash.

   If clouds were good conductors. The charge separation itself would fail. The positive ice particles above and negative water droplets below could not remain apart inside a conducting cloud; they would neutralise as fast as the up-and-down winds separated them.

   ✦ The general principle is worth more than the particular answer: a sudden, violent release requires something to hold the store in place beforehand. Remove the insulation and you remove the storage; remove the storage and there is nothing left to release. The same logic explains why a lightning conductor works — it deliberately provides easy path for the transfer of electric charges into the ground, so the charge never builds up through the building.

7. 74 marksCuriosity Grade 8, Chapter 6, page 96, exercise 7

   What will happen to the two identical balloons A and B in Fig. 6.24 when water is filled into the bottle up to a certain height? Will both balloons bulge? If yes, will they bulge equally? Explain.

   Hint. Note where on the bottle the two balloons are attached — and at what height.

   Yes, both balloons bulge — and they bulge equally.

   Why they bulge at all. The balloons are fitted to openings in the sides of the bottle, not the bottom. They inflate only because liquids exert pressure not only at the bottom of the container, but also on its sides. In fact liquids exert pressure in all directions. This is Activity 6.2 — the bottle with four side holes from which water spurted out.

   Why they bulge equally. The two openings are at the same height on the bottle, so the column of water standing above each is the same height. And the pressure exerted by a liquid in a vessel depends on the height of its column — Activity 6.1. Equal column heights, equal pressures, equal bulges.

   ✦ The answer needs both activities, and that is why this question is set. Activity 6.2 tells you the balloons bulge; Activity 6.1 tells you they bulge the same amount. Neither on its own answers the whole question.

   Two predictions that follow, and are worth adding:

   • Pour in more water and both bulges grow together, since both columns get taller by the same amount.
   • If one balloon were fitted lower on the bottle, that one would bulge more, because it would have a taller column above it.

   Neither the shape of the bottle nor the total amount of water it holds affects the answer — only the height of water above each opening.

8. 85 marksCuriosity Grade 8, Chapter 6, page 96, exercise 8

   Explain how a storm becomes a cyclone.

   Hint. Two extra ingredients turn an ordinary storm into a spinning system.

   A storm becomes a cyclone when it forms over warm ocean water and two further things happen: the heat released by condensation drives it harder, and Earth's rotation makes it spin.

   The full chain:

   1. Cyclones are large storms that form over warm ocean waters. As the ocean water gets heated, the warm and moist air above it rises.
   2. As the moist air rises, the water vapour condenses to form raindrops.
   3. The feedback. During evaporation, water takes up heat to change into vapour. When this water vapour condenses into raindrops, heat is released back into the atmosphere. This causes further warming of the ascending air leading it to rise even further, creating an even lower pressure.
   4. Air from the surrounding regions rushes in and it also starts rising.
   5. The spin. Earth's rotation causes the moving air to spin.
   6. This cycle is repeated, resulting in the creation of a very low-pressure area with high-speed winds revolving around it.

   And that is a cyclone: This spinning system of clouds, winds, and rain is called a cyclone.

   ✦ Step 3 is what makes the difference in strength, and step 5 the difference in shape. Without the released heat, the low pressure would not deepen and the winds would stay at ordinary storm strength — the chapter notes that a cyclone generates higher wind speeds compared to the wind speeds produced by regular thunderstorms. Without the rotation, the inrushing air would flow straight in rather than revolving, and there would be no spinning system and no eye.

   Warm ocean water is the fuel, which is why once the cyclone reaches land, the source of moist air is cut off and it gradually loses its strength.

9. 95 marksCuriosity Grade 8, Chapter 6, page 96, exercise 9

   Fig. 6.25 shows trees along a sea coast on a summer afternoon, with A on the left and B on the right. All the trees lean and their fronds stream towards A. Identify which side is land — A or B. Explain your answer.

   Hint. Read the wind direction off the trees first, then ask which way a daytime breeze blows.

   A is the land, and B is the sea.

   Step 1 — read the wind direction from the trees. Every trunk leans towards A and all the fronds are swept towards A. Trees bend in the direction the wind pushes them, so the wind is blowing from B towards A.

   Step 2 — work out which way a daytime breeze blows. It is a summer afternoon, so this is the daytime case. As land gets heated faster than water during the day, the air above the land becomes warmer and lighter. Hence, it rises, creating an area of low pressure. The air from the high pressure region of the sea blows to the low pressure region which develops on the land, resulting in a sea breeze.

   So in the afternoon the wind blows from the sea to the land.

   Step 3 — put the two together. The wind blows from B to A, and it blows from sea to land. Therefore B is the sea and A is the land.

   	Side A	Side B
   What it is	Land	Sea
   Heating on a summer afternoon	Heats faster	Stays cooler
   Pressure	Low	High
   Wind	Blows towards it	Blows away from it

   ✦ The word afternoon is the whole question. At night the answer would reverse: the sea stays warmer, the low pressure forms over the sea, and a land breeze blows from land to sea — so the same picture of trees at night would put the land at B. Never answer this kind of question without checking the time of day.

   And remember the naming convention: a sea breeze is named for where it comes from, not where it goes.

10. 104 marksCuriosity Grade 8, Chapter 6, page 96, exercise 10

    Describe an activity to show that air flows from a region of high pressure to a region of low pressure.

    Hint. Give method, observation, reasoning and conclusion — the reasoning is where the marks are.

    Activity: two balloons connected by a straw (Activity 6.5, Fig. 6.12).

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

    Method.

    1. Insert one end of the straw into an uninflated balloon and tie it tightly with a rubber band.
    2. Inflate the second balloon and hold its mouth closed with your fingers so that no air escapes.
    3. Insert the free end of the straw into the neck of the inflated balloon and tie it, taking care that no air leaks as you do so.
    4. Predict what will happen, then release your grip and observe both balloons.

    Observation. The inflated balloon becomes smaller and the uninflated one becomes bigger. After some time both are almost the same size and the flow stops.

    Reasoning. The air in the inflated balloon was at a higher pressure than the air in the empty one, so air travelled through the straw from the high-pressure balloon to the low-pressure one. The air flow stops when the pressure in both balloons becomes equal — showing that it was the pressure difference that was driving the flow, and nothing else.

    Conclusion. Air moves from a region of high air pressure to a region of low air pressure.

    ✦ Include the stopping, or the answer is incomplete. That air moved only shows a flow happened; plenty of explanations could give that. It is the flow ceasing at the exact moment the two pressures match — with plenty of air still in both balloons — that identifies the pressure difference as the cause.

    Make sure every join is airtight. If air escapes into the room at either end, it never travels down the straw and the experiment shows nothing.

11. 115 marksCuriosity Grade 8, Chapter 6, page 96, exercise 11

    What is a thunderstorm? Explain the process of its formation.

    Hint. Start from heated land, not from the flash.

    Definition. A storm accompanied by lightning and thunder is called a thunderstorm. The two things it needs, from the Snapshots, are moisture and strong winds.

    Formation, stage by stage.

    Stage 1 — rising air and circulation. When land gets heated, the warm and moist air, being lighter, rises, thereby creating a low pressure area. Cooler air from the surrounding high-pressure areas flows to take its place. This air, in turn, gets heated and rises. This results in a continuous process of wind circulation.

    Stage 2 — clouds and rain. As the rising air expands, it cools and moisture in it condenses to form water droplets, creating clouds. The water droplets merge to form heavier drops, which come down as rain, hail, or snow. Strong winds with rain make it a storm.

    Stage 3 — ice and charges. Under certain conditions, warm air rises to great heights that the low temperature there converts water droplets into ice particles. Strong winds blowing upwards and downwards rub the ice particles and water droplets together and cause static electric charges to develop within the clouds. Lighter positive ice particles rise to the upper part of the cloud, heavier negative water droplets stay low.

    Stage 4 — lightning and thunder. Air normally insulates, but when the charge build-up becomes very large its insulating property breaks down. The sudden flow of charges gives the flash of lightning, and the air it heats expands to make the sound of thunder.

    ✦ Every thunderstorm is a storm, but not every storm is a thunderstorm. Stages 1 and 2 give you a storm. Stages 3 and 4 are what must be added — and they happen only if the air rises high enough and cold enough to form ice particles, and the up-and-down winds are strong enough to rub them together.

    In hot, humid, and tropical regions like India, storms are more frequent — hot supplies the heating, humid supplies the moisture.

12. 124 marksCuriosity Grade 8, Chapter 6, page 96, exercise 12

    Explain the process that causes lightning.

    Hint. Charge separation, then the breakdown of air — both halves are needed.

    Step 1 — charges are created. Under certain conditions the rising warm air reaches heights cold enough to turn water droplets into ice particles. Strong winds blowing upwards and downwards facilitate rubbing between water droplets and ice particles, and — as you learnt in Exploring Forces — rubbing two objects together charges them. So static electric charges develop within the cloud.

    Step 2 — the charges separate.

    	Charge	Position
    Lighter ice particles	Positive	Move upwards and occupy the upper part of the clouds
    Heavier water droplets	Negative	Occupy the lower part of the clouds

    Also, when the negatively charged lower part of the cloud moves closer to the ground, it causes the ground and nearby objects, such as trees or buildings, to become positively charged.

    Step 3 — air breaks down. Normally, air acts as an electrical insulator and does not let opposite charges meet. But when the build up of charges becomes very large, the insulating property of air breaks down. A sudden flow of charges takes place, producing a bright flash of light called lightning.

    Where it happens. Lightning can occur as opposite charges collide within a cloud, between clouds, or between clouds and the ground.

    And the sound. Lightning rapidly heats up the air around it, causing the air to expand and produce a loud sound known as thunder.

    ✦ Step 3 is what most answers leave out, and it is the step that explains the violence. If air did not insulate, charge would trickle away as fast as it formed, so there would be nothing left to release. It is the accumulation, held back by the air until it can be held no longer, that makes lightning a sudden brilliant flash rather than a slow leak. Exercise 6 tests precisely this.

13. 134 marksCuriosity Grade 8, Chapter 6, page 96, exercise 13

    Explain why holes are made in banners and hoardings.

    Hint. A banner in a strong wind has the same problem as a roof in a storm.

    So that high-speed wind can pass through them, instead of building up a large pressure difference between the two faces.

    The reasoning.

    1. A banner or hoarding is a large flat sheet with a big surface area.
    2. When strong wind blows across it, high speed winds are accompanied by a reduced air pressure — so the pressure on the windward face falls, while the sheltered side keeps a higher pressure.
    3. That difference acts over the whole area of the banner, and since force = pressure × area, a large area turns even a modest pressure difference into a very large force.
    4. The result can be a torn banner, or a hoarding whose frame is bent or brought down.
    5. Holes let air pass from one side to the other, so the two faces come much closer to the same pressure, the difference is reduced, and so is the force.

    ✦ This is exactly the advice about opening doors and windows during a storm, applied to a flat sheet. In both cases the fix is not to resist the wind but to let it through, removing the pressure difference rather than trying to stand up to it:

    Structure	The problem	The remedy
    Roof in a storm	Low pressure above, high inside	Open the doors and windows
    Banner or hoarding	Low pressure on one face	Cut holes through it

    Notice the trade-off being accepted. The holes make the printed message slightly less complete — a small cost for a banner that survives the first strong wind. Engineers make this kind of judgement all the time, and it is worth naming it in your answer.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity, Textbook of Science for Grade 8, Chapter 6 'Pressure, Winds, Storms, and Cyclones', book pages 80-97 (hecu106.pdf, 18 pages, Reprint 2026-27), downloaded from ncert.nic.in and read page by page. Every activity number, figure number, quantity and quoted sentence below was checked against that PDF. THREE FIGURES WERE MEASURED, NOT EYEBALLED, because three exercise answers turn on them. Fig. 6.22 (exercise 1(iv)) was rendered at 900 dpi and the vessel walls located from the dark outlines: vessel A is 519 px wide and vessel B is 726 px, so B is 1.40x wider, while the water columns measure 660 px and 671 px - equal to within 1.7%, matching the question's premise of equal levels. Hence P_A = P_B but F_A < F_B, answer (b). Fig. 6.24 (exercise 7) was segmented by colour: the two balloons occupy identical vertical ranges (rows 1260-1403, centroids both at row 1334), so they are at exactly the same height and bulge equally. Fig. 6.25 (exercise 9) was measured by tracking the palm trunks: the leftmost trunk's centre moves from x=655 at the top to x=763 near the base, so the crown sits about 108 px LEFT of the base, and all four crowns stream leftwards - the wind blows from B to A. Since a summer afternoon gives a SEA BREEZE (sea to land), B is the sea and A is the land. Fig. 6.21 was also rendered and confirmed to show the three vessels JOINED BY TUBES near their bases, which is what makes answer (d) correct. The chapter's own atmospheric-pressure figure was checked rather than assumed: 2250 N over 15 cm x 15 cm = 0.0225 m^2 gives 1,00,000 Pa = 1000 hPa = 1000 mb, which sits squarely inside the 994-1008 mb range marked on Fig. 6.19, so the book's number is internally consistent. Two deliberate restraints. (1) The chapter names exactly ONE cyclone (Amphan 2020, peak winds 270 km/h) and one surge range (3-12 m), and gives no cyclone categories, no casualty figures, no monsoon rainfall percentages and no atmospheric composition percentages. None are supplied here; the research projects tell the student to cite IMD or an equivalent checked source and to report disagreement between sources rather than pick a number. (2) Lightning-safety advice is reproduced exactly as the book gives it, with nothing added, since an invented extra rule could put someone at risk.. Questions are referenced from the NCERT textbook for identification.