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Pressure, Winds, Storms, and Cyclones – Class 8 Science notes, important questions and MCQs
NCERT Class 8 Science, chapter 6. Notes, key terms, important questions with answers and MCQs.
Chapter overview
Pressure is force per unit area. Differences in air pressure create winds, and warm moist air over seas can grow into thunderstorms and cyclones.
Pressure
- Pressure = force / area; unit pascal (N/m²). Sharp knives and narrow nails have small area, so high pressure.
- Liquid pressure increases with depth and acts in all directions (dams are thicker at the bottom).
- Air exerts pressure (atmospheric pressure); a straw and a syringe work because of it.
Winds and cyclones
- Air moves from high pressure to low pressure — this is wind.
- Warm air rises, creating low pressure; uneven heating of land and sea causes sea breeze and monsoons.
- Cyclones form over warm seas: a low-pressure "eye" surrounded by strong winds and heavy rain.
- Safety: follow IMD warnings, move to cyclone shelters, store water and food.
Key terms
- Pressure
- force acting per unit area
- Wind
- moving air
- Cyclone
- a large storm with low pressure at the centre and spiralling winds
Formulas
- P = F / A
- Liquid pressure P = hρg
Important questions with answers
Why do school bags have wide straps?2 marks
Wide straps increase the area in contact with the shoulder, so the pressure is less and the bag feels lighter.
How is wind formed?3 marks
Unequal heating of the Earth's surface makes air over warm areas rise, creating low pressure. Air moves from high-pressure areas to low-pressure areas; this moving air is wind.
How does a cyclone form? List three safety measures before and during a cyclone.5 marks
Over warm oceans, water evaporates and warm moist air rises, creating very low pressure. Air rushes in from all sides and starts spinning; as vapour condenses it releases heat that makes the air rise faster, building a strong rotating storm with a calm "eye" at the centre. Safety: follow warnings from IMD on radio, TV or phone; move to a safe shelter away from the coast and low areas; keep drinking water, dry food, torch and first-aid ready, and do not go out or touch fallen electric wires during the storm.
Quick revision
- Air moves from high to low pressure.
- Pressure in liquids increases with depth.
- The eye of a cyclone is calm.
Exam tips
- Same force on a smaller area gives more pressure — school bag straps are wide to reduce pressure.
- In India, cyclones are common on the east coast (Odisha, Andhra Pradesh) in May and Oct–Nov.
Practice MCQs
The SI unit of pressure is
- pascal
- newton
- joule
- watt
Show answer
Answer: (a) pascal. Pascal.
Wind blows from
- low to high pressure
- hot to cold land only
- only east to west
- high to low pressure
Show answer
Answer: (d) high to low pressure. High to low.
A force of 100 N acts on 2 m². The pressure is
- 200 Pa
- 102 Pa
- 50 Pa
- 98 Pa
Show answer
Answer: (c) 50 Pa. 100 ÷ 2.
Dams are thicker at the bottom because
- water is colder there
- it looks better
- water pressure increases with depth
- fish live there
Show answer
Answer: (c) water pressure increases with depth. Pressure increases with depth.
Pressure =
- force ÷ area
- force × area
- area ÷ force
- force + area
Show answer
Answer: (a) force ÷ area. P = F/A.
The calm centre of a cyclone is called the
- wall
- eye
- funnel
- front
Show answer
Answer: (b) eye. Eye.
Why do camels have broad feet?
- to run faster
- to reduce pressure on sand
- to store water
- to dig
Show answer
Answer: (b) to reduce pressure on sand. Larger area, less pressure.
Why are the walls of a dam thicker at the bottom
- to look strong
- because of wind
- to save cement
- water pressure increases with depth
Show answer
Answer: (d) water pressure increases with depth. Liquid pressure rises with depth.
All chapters of Class 8 Science
Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.