Probe and Ponder — The Opening Questions — Pressure, Winds, Storms, and Cyclones

1. 13 marksCuriosity Grade 8, Chapter 6, page 80

   Why are winds stronger on some days than on others?

   Hint. Wind is air on the move. What makes air move at all?

   Because the difference in air pressure between two regions is greater on some days than on others.

   The chapter establishes two facts that together answer this:

   1. Air moves from a region of high air pressure to a region of low air pressure — this is what wind is (Activity 6.5).
   2. If we could measure the speed of the escaping air in Activity 6.5, we would find that the speed of the air is higher if the pressure difference is higher.

   So the wind's strength is set by how large the pressure difference is, not by how much air there is.

   ✦ Where the pressure differences come from. Warm air rises, creating a low-pressure area. Cooler air from surrounding higher-pressure regions moves in to take its place. On a day when one region is heated much more strongly than its surroundings, the difference is large and the wind is strong. On a day when everything is heated evenly, the difference is small and the air is calm.

   The extreme case is in this same chapter. A cyclone is a very low-pressure area with high-speed winds revolving around it — an enormous pressure difference, and correspondingly enormous wind speeds. Fig. 6.19 shows the pressure falling from 1008 mb at the edge to 994 mb at the centre.

2. 23 marksCuriosity Grade 8, Chapter 6, page 80

   Why are water tanks usually placed at a height?

   Hint. Activity 6.1 answers this exactly.

   Because the pressure a liquid exerts depends on the height of its column. The higher the tank, the taller the column of water above the tap, and the greater the pressure at the tap.

   The chapter's own words: This is the reason why overhead tanks are placed at a height so that the pressure in the taps is increased, resulting in a good stream of water from the taps.

   The evidence for it is Activity 6.1. Balloons tied to the bottom of water-filled pipes bulge more as the height of the water column is increased, and equally for equal heights — even when the pipes have different diameters and therefore hold different weights of water.

   ✦ The counter-intuitive part. It is not the amount of water that matters. A wide tank holding far more water, but placed at the same height, gives exactly the same pressure at the tap. That is why exercise 1(iii) offers 'a tank of the same height that can hold more water' as a wrong option — more water at the same height changes nothing.

   A consequence you can check at home. In a three-storeyed building with the tank on top, the ground-floor tap has the tallest column above it and gives the strongest stream; the top floor has the shortest column and the weakest.

3. 34 marksCuriosity Grade 8, Chapter 6, page 80

   Can air pressure really crush us?

   Hint. The chapter gives a number. Work out why we survive it.

   The force is genuinely enormous, and yet it does not crush us — for a reason the chapter states plainly.

   How large the force is. The force exerted by the atmospheric air column over an area 15 cm × 15 cm is nearly equal to the force of gravity on an object of mass 225 kg (2250 N). That is a patch about the size of a school notebook cover carrying the equivalent of three or four adults.

   Why we are not crushed. The reason we are not crushed under this weight is that the pressure inside our bodies is also equal to the atmospheric pressure. This balances the pressure exerted from outside. The pressure inside our body is caused by the movement of fluids and gases in tissues and organs of the body.

   ✦ Check the chapter's number for yourself. 15 cm × 15 cm = 0.15 m × 0.15 m = 0.0225 m². So

   pressure = force ÷ area = 2250 N ÷ 0.0225 m² = 1,00,000 N/m²

   which is 1,00,000 Pa, or 1000 hPa — and the chapter's A step further box tells you that air pressure is usually quoted in hectopascal or millibar. Fig. 6.19 shows ordinary pressures of 998 to 1008 mb. The book's figure is exactly consistent with them, which is a good sign that it is a real measurement and not a rough guess.

   What crushing would actually require is not more air pressure but a difference in pressure — which is precisely why a rubber sucker sticks so hard in Activity 6.4.

4. 44 marksCuriosity Grade 8, Chapter 6, page 80

   What causes storms and cyclones? If the Earth stopped rotating, would cyclones still form?

   Hint. The second half asks you to remove one step from the chapter's chain and see what breaks.

   What causes them, in the chapter's chain: land or ocean water is heated → the warm, moist air above it rises → a low pressure area forms → cooler air from surrounding high-pressure regions rushes in → that air is heated and rises in turn → the rising air cools, its moisture condenses into droplets, forming clouds and rain. The strong winds accompanied by rain is called a storm.

   For a cyclone, over warm ocean water, one extra step drives it much harder: when the water vapour condenses, 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. Then — Earth's rotation causes the moving air to spin.

   If the Earth stopped rotating. The chapter names Earth's rotation as the step that makes the inrushing air spin rather than simply flow straight in. Without it you would still have the heating, the rising moist air, the low pressure and the inrush of surrounding air — so you would still get storms with strong winds and heavy rain. What you would not get is the spinning system with an eye at its centre, and this spinning system of clouds, winds, and rain is called a cyclone.

   ✦ How far the chapter lets you take this. It gives rotation as a necessary ingredient of the spin and no more. Exactly what a non-rotating Earth's weather would look like is a research question, not something this book answers — the honest reply names the step that is removed and says what depends on it, without inventing the rest.

5. 53 marksCuriosity Grade 8, Chapter 6, page 81

   The chapter opens with fallen leaves swirling, trees bending, doors slamming and clothes fluttering. What single idea connects all four, and what does the chapter say it will explore?

   Hint. The opening paragraph names the quantity in its last two sentences.

   The connecting idea is wind pressure. The force exerted by wind creates wind pressure which causes these effects.

   Observation	What the wind is doing
   Fallen leaves rise and swirl	The wind exerts a force on them, making them move from rest
   Trees sway or bend	A force on the leaves and branches, changing their shape and position
   Doors slam, windows rattle	A force pushing on a large flat area
   Clothes flutter	The same force, on a light flexible sheet

   ✦ Notice the step the paragraph takes. From Exploring Forces you already know that a push can move an object, change its speed, its direction or its shape. What is new here is that the wind's push is spread over an area — a whole door, a whole tree, a whole sheet of cloth — and that is why the chapter needs a new quantity, force per unit area, before it can go any further.

   What the chapter says it will do: In this chapter, we will explore the relationship between force and pressure, and understand how they shape powerful natural events like thunderstorms and cyclones. The route runs from a schoolbag strap on page 81 to a cyclone on page 92, and every step in between is about pressure.

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.