Learning Objectives
- Understand properties of air and air pressure
- Learn how winds are caused
- Understand thunderstorms and cyclones
- Know safety measures during cyclones
Key Concepts
Air Pressure
Air exerts pressure in all directions. This can be demonstrated by many experiments (collapsing can experiment, straw drinking).
Key principle: Air moves from regions of high pressure to regions of low pressure. This movement of air is called wind.
How Winds Are Caused
Unequal heating of air on earth causes wind:
- Unequal heating of land and water: Land heats faster than water during day â warm air over land rises â cool air from sea rushes in (sea breeze). At night, the reverse happens (land breeze).
- Unequal heating of equator and poles: Equatorial regions receive more heat â warm air rises â cool air from poles moves towards equator â causes global wind patterns.
Properties Related to Wind
- Warm air rises (less dense) creating low pressure.
- Cool air sinks (more dense) creating high pressure.
- Wind speed increases when pressure difference is large.
- Air expands on heating and contracts on cooling.
Thunderstorms and Cyclones
Thunderstorm: Develops in hot, humid conditions. Upward movement of warm moist air creates cumulonimbus clouds â lightning, thunder, heavy rain, and strong winds.
Cyclone: A very large, powerful storm with wind speeds over 119 km/h. Warm moist air rises rapidly, creating very low pressure centre (eye). Surrounding air spirals inward. Eye is calm; surrounding area has violent winds and heavy rain.
Tornado: A violent, funnel-shaped spinning wind. Smaller but more intense than cyclone. Wind speeds can exceed 300 km/h.
Safety Measures During Cyclones
- Stay indoors, away from windows
- Do not go near damaged power lines
- Keep emergency supplies ready
- Follow weather warnings and evacuate if advised
- Do not shelter under isolated trees
Summary
Air moves from high to low pressure areas, creating wind. Unequal heating causes pressure differences. Thunderstorms form from rising warm moist air. Cyclones are massive storms with low pressure centres. Safety precautions should be followed during severe weather events.
Important Terms
- Air pressure: Force exerted by air on surfaces
- Wind: Moving air from high to low pressure
- Cyclone: Large storm with spiralling winds around a low-pressure centre
- Tornado: Violent funnel-shaped spinning wind
- Eye of cyclone: Calm, low-pressure centre
Quick Revision
- Wind: High pressure â Low pressure
- Warm air rises â low pressure; Cool air sinks â high pressure
- Sea breeze: day (sea â land); Land breeze: night (land â sea)
- Cyclone = large, spinning storm with eye
- Tornado = small but very intense funnel wind