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Why does a bag with thin straps hurt more than one with broad straps, even when both weigh the same? Why does a cyclone have a calm centre? Chapter 6 of the new Class 8 science book links these questions through one idea: pressure. This post explains the chapter, works through the sums, flags the usual mistakes and gives a practice plan.
Where is this topic in the new book?
NCERT's Class 8 science textbook is Curiosity, Grade 8. Its contents page (Reprint 2026-27) lists 13 chapters, with Chapter 6 titled "Pressure, Winds, Storms, and Cyclones". The Chapter 6 PDF covers pressure in solids and liquids, air pressure, how wind forms, why fast winds lower pressure, thunderstorms and lightning, and cyclones. It comes straight after Chapter 5, "Exploring Forces", and there is no separate "Force and Pressure" chapter in this edition.
What is pressure, and how do you calculate it?
The chapter defines pressure as force per unit area, counting only the force acting perpendicular to the surface:
Pressure = Force ÷ Area
The SI unit is newton per square metre (N/m²), also called the pascal (Pa). The book's own example: 100 N on 2 m² gives 100 ÷ 2 = 50 Pa.
Worked example: bag straps. These are sample numbers. A school bag weighs 60 N and hangs on two straps.
Narrow straps, each touching 2 cm × 5 cm = 10 cm² of shoulder. Total area = 20 cm² = 0.002 m². Pressure = 60 ÷ 0.002 = 30,000 Pa.
Broad straps, each touching 5 cm × 10 cm = 50 cm². Total area = 100 cm² = 0.01 m². Pressure = 60 ÷ 0.01 = 6,000 Pa.
Same weight, one-fifth of the pressure. The key step is the unit change: 1 m² = 10,000 cm², so 20 cm² = 0.002 m².
Do liquids and air exert pressure too?
Yes. In the chapter's balloon activity, two pipes of different widths are filled with water to the same height, and the balloons at the bottom bulge equally even though the wide pipe holds more water. Liquid pressure depends on the height of the column, not the amount of water. That is why overhead tanks sit on rooftops, and why a dam is built broader at the base, where the water pushes hardest. Liquids push in all directions, including sideways through holes in a bottle.
Air presses on us too. The book says the air above a 15 cm × 15 cm square pushes down with a force of nearly 2,250 N, about the weight of a 225 kg mass. We are not crushed because the pressure inside our bodies balances it.
Worked example: check the book's number. NASA's Earth fact sheet gives average surface pressure as 1,014 mb. The chapter explains that 1 millibar = 1 hectopascal = 100 Pa, so 1,014 mb = 101,400 Pa.
Area = 0.15 m × 0.15 m = 0.0225 m².
Force = 101,400 × 0.0225 ≈ 2,282 N.
The book's 2,250 N comes from rounding air pressure to 100,000 Pa (100,000 × 0.0225 = 2,250). Both say the same thing: air pressure is large.
How do winds, storms and cyclones form?
The chapter connects pressure differences to the sea breeze you met in Class 7: land heats faster by day, air above it rises, pressure drops, and air flows in from the sea.
Fast-moving air also has lower pressure. Blow between two hanging balloons and they move together. During a storm, fast wind over a roof lowers the pressure above it, and a weak roof can lift off. The book says keeping doors and windows open during such storms reduces the pressure difference.
In a thunderstorm, warm moist air rises, cools and forms clouds. Strong up and down winds rub ice particles and water droplets together and separate charge: lighter, positively charged ice moves up, heavier negative droplets stay lower. When the charge becomes large, air stops insulating and a spark, lightning, jumps.
A cyclone, the chapter explains, forms over warm ocean water. Moist air rises, its water vapour condenses and releases heat, the air rises further and pressure drops more. Air rushes in, and Earth's rotation makes it spin. NOAA's introduction to tropical cyclones lists warm ocean water of at least 27 °C as one of the conditions needed. NASA's SpacePlace guide adds that storms north of the equator spin counterclockwise.
Worked example: pressure difference in a cyclone. The book's cyclone diagram shows 1,008 mb at the edge and 994 mb near the centre. Difference = 14 mb = 1,400 Pa. On every square metre, that is an unbalanced push of 1,400 N towards the centre.
What mistakes do students make in this chapter?
"Wind blows from low to high pressure." It is the other way round.
"More water means more pressure." At the bottom of a container, the height of the water column decides it.
Forgetting to convert cm² to m² before dividing. Divide cm² by 10,000.
"The eye of a cyclone is the most violent part." The eye is calm with the lowest pressure; the strongest winds and rain are around it. The chapter's true-or-false exercise tests this.
Lying flat in a lightning storm. The book says crouch in a low open area, minimise contact with the ground, and do not lie down. Inside a car or bus is comparatively safer.
A practice plan
Do the chapter's elephant problem (20,000 N on four feet of 0.25 m² each) and the two-boat problem, showing units at each step.
Make your own strap or knife example with sample numbers.
Draw a labelled diagram of sea breeze and land breeze from memory.
Explain to someone at home, in five steps, how a storm becomes a cyclone.
Write the lightning safety rules on a card and keep it with your emergency kit.
If pressure in fluids still feels abstract, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read. When you reach Class 11, our post on fluids and Bernoulli mistakes builds on the fast-air, low-pressure idea.
Try it today: weigh your school bag, measure the straps, and calculate the pressure on your shoulders.
