Science · Class 8 · Chapter 6

Pressure, Winds, Storms, and Cyclones

Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
  • Pressure — Force per unit area; SI unit N/m² (pascal).
  • Atmospheric pressure — The pressure exerted by air around us.
  • Wind — Air moving from high to low pressure.
  • Sea breeze / Land breeze — Sea-to-land wind by day / land-to-sea by night.
  • Thunderstorm — A storm with lightning and thunder.
  • Lightning conductor — A rod giving lightning a safe path to ground.
  • Cyclone — A spinning storm system over warm ocean water.
  • Eye of the cyclone — The calm, lowest-pressure centre.
40 min lesson

Chapter 6 · Concept 1 of 13

Pressure = Force ÷ Area

  • The same weight (force) feels different depending on how much area it's spread across.
  • Worked example — A force of 100 N spread over 2 m² gives a pressure of 100 ÷ 2 = 50 N/m². The SI unit of pressure is N/m², also called the pascal (Pa).

Chapter 6 · Concept 2 of 13

Liquids Exert Pressure

  • Height matters — As a liquid column's height increases, so does the pressure at the bottom — that's why overhead water tanks are placed high, to boost tap pressure.
  • A dam's shape makes sense now — A dam's base is built broader than its top, because water pressure is greatest near the bottom.

Chapter 6 · Concept 3 of 13

Liquids Press in Every Direction

  • Sideways too — Liquids press on the sides of a container, not only the bottom — shown by water spurting sideways from holes made at the same height around a bottle.

Chapter 6 · Concept 4 of 13

Atmospheric Pressure

  • The atmosphere — the envelope of air around Earth — exerts pressure on everything, all the time.
  • We aren't crushed because... — The pressure inside our bodies balances the pressure of the air outside. A rubber sucker sticks to a surface for the same reason — pushing out the air beneath it lowers the pressure inside.

Chapter 6 · Concept 5 of 13

How Wind Forms

  • Wind — Air always moves from a region of high pressure to a region of low pressure. The greater the pressure difference, the higher the wind speed.

Chapter 6 · Concept 6 of 13

Sea Breeze and Land Breeze

  • Daytime: sea breeze — Land heats faster than water. Warm air rises over the land, creating low pressure — so wind blows from sea to land.
  • Night: land breeze — Land cools faster than the sea. Now the (relatively warmer) sea has low pressure — so wind blows from land to sea.

Chapter 6 · Concept 7 of 13

Fast Wind Means Lower Pressure

  • High-speed winds are accompanied by reduced air pressure above the moving air.
  • Why open windows in a storm — Strong wind over a roof creates low pressure above it. If the pressure difference is large, a weak roof can blow off — keeping doors and windows open reduces this difference.

Chapter 6 · Concept 8 of 13

How a Thunderstorm Forms

  • Warm moist air rises
  • Cools, forms clouds & rain
  • Strong winds separate charge
  • Charge builds up, then discharges

Chapter 6 · Concept 9 of 13

Lightning and Thunder

  • Lightning — Positive charge (lighter ice) collects at the top of a cloud, negative charge (heavier droplets) lower down. When the charge builds up enough, it discharges suddenly as a bright flash.
  • Thunder — Lightning rapidly heats the surrounding air, making it expand suddenly — producing the loud sound of thunder.

Chapter 6 · Concept 10 of 13

Lightning Safety

  • During a storm — Stay away from tall objects, crouch in a low, open area, don't lie flat, avoid metal-rod umbrellas, and get out of water. A car is comparatively safe.
  • Lightning conductor — A pointed metal rod on a building, connected to the ground, gives lightning a safe path to discharge — protecting the building.

Chapter 6 · Concept 11 of 13

How a Cyclone Forms

  • Over warm ocean water, rising warm moist air lowers pressure further as its water vapour condenses and releases heat.
  • Earth's rotation adds the spin — Surrounding air rushes in and rises too, and Earth's rotation makes the whole system spin — creating a cyclone.

Chapter 6 · Concept 12 of 13

The Eye of the Cyclone

  • Strong winds & heavy rain

Chapter 6 · Concept 13 of 13

Cyclone Effects, and Watching the Sky

  • Destruction — Storm surges 3–12 m high, flooding, contaminated water and farmland, blocked roads, and power outages. Cyclones weaken once they move over land.
  • Tracking and warning — The India Meteorological Department (IMD) tracks weather and issues cyclone alerts. Satellites help predict cyclone paths to reduce their impact.

Quick Recap

Check Your Understanding

  1. 1True or False: (i) Air flows from higher to lower pressure. (ii) Liquids exert pressure only at the bottom of a container. (iii) The weather is stormy at the eye of a cyclone. (iv) It's safer to be in a car during a thunderstorm.
  2. 2A boy lying flat on loose sand sinks less than the same boy standing upright on it. Why?
  3. 3An elephant stands on four feet, each covering 0.25 m². If it weighs 20,000 N, what pressure does it exert on the ground?