Chapter 16: Winds, Storms, and Cyclones 🌪️
A Comprehensive Guide for PSTET Paper-2 (Science)
Chapter Overview
| Section | Topic | PSTET Weightage | Page No. |
|:---:|:---|::---:|:---:|
| 16.1 | Air Exerts Pressure | High | 2 |
| 16.2 | High Speed Winds and Reduced Pressure (Bernoulli's Principle - Basic) | Medium | 7 |
| 16.3 | Formation of Thunderstorms and Cyclones | High | 12 |
| 16.4 | Safety Measures during Cyclones | High | 19 |
| Practice Zone | MCQs & Pedagogical Questions | - | 25 |
Learning Objectives 🎯
After studying this chapter, you will be able to:
✅ Demonstrate through simple experiments that air exerts pressure in all directions
✅ Explain Bernoulli's principle and its application in everyday phenomena (flying airplanes, roof blowing during storms)
✅ Describe the formation of thunderstorms and cyclones with the required conditions
✅ Differentiate between thunderstorms, cyclones, hurricanes, and typhoons
✅ List and explain essential safety measures to be taken before, during, and after a cyclone
✅ Apply pedagogical strategies to teach wind and storm concepts effectively to upper primary students
Pedagogical Link 🔗
For Teachers: This chapter directly aligns with:
Class 7 Science NCERT Chapter 8: "Winds, Storms and Cyclones"
Teaching Tips:
Begin with simple demonstrations—blowing between two hanging paper strips to show Bernoulli's principle
Use hands-on experiments like the "flying paper" activity to make abstract concepts concrete
Create a "storm in a bottle" using two-liter plastic bottles to demonstrate vortex formation
Connect to current events—discuss recent cyclones in news (Amphan, Fani, etc.)
Use videos and animations from NOAA and other sources to show satellite imagery of cyclones
Section 16.1: Air Exerts Pressure 💨
Introduction
We live at the bottom of an ocean of air. Although we cannot see it, air has substance and exerts pressure on everything it touches. Understanding air pressure is fundamental to explaining winds, storms, and cyclones .
16.1.1 What is Air Pressure?
Definition: Air pressure is the force exerted by the weight of air molecules on a surface.
Key Concept: Air has weight! A cubic meter of air weighs about 1.2 kilograms. The column of air above us, extending to the top of the atmosphere, exerts tremendous pressure—about 1 kilogram per square centimeter at sea level.
Table 16.1: Air Pressure Facts
| Fact | Details |
|---|---|
| Atmospheric pressure at sea level | 101,325 Pascals (Pa) or 1 atmosphere (atm) |
| Equivalent weight | About 10,000 kg (10 tonnes) on an average human body! |
| Why we aren't crushed | Air pressure acts equally in all directions; our bodies exert equal internal pressure |
| Measurement instrument | Barometer (invented by Evangelista Torricelli in 1643) |
16.1.2 Simple Experiments to Demonstrate Air Pressure
These experiments are excellent for classroom demonstrations and help students understand that air, despite being invisible, exerts pressure .
A. The Water Glass Trick 🥛
| Step | Procedure |
|---|---|
| 1 | Fill a glass completely with water |
| 2 | Place a stiff cardboard or plastic sheet over the mouth of the glass |
| 3 | Hold the cardboard firmly and invert the glass |
| 4 | Carefully remove your hand from the cardboard |
| Observation | The cardboard stays in place and the water does not spill |
| Explanation | Air pressure pushing upward on the cardboard is greater than the weight of the water pushing downward |
B. The Can-Crushing Experiment 🥫
| Step | Procedure |
|---|---|
| 1 | Take an empty aluminum soda can with a small amount of water |
| 2 | Heat the can on a hot plate until steam comes out (water boils) |
| 3 | Using tongs, quickly invert the can into a bowl of cold water |
| Observation | The can crushes instantly with a loud pop |
| Explanation | Heating drives out air; cooling condenses steam, creating vacuum inside; atmospheric pressure from outside crushes the can |
C. Straw Through Potato 🥔
| Step | Procedure |
|---|---|
| 1 | Take a drinking straw and a raw potato |
| 2 | Hold the straw vertically and try to push it through the potato (difficult) |
| 3 | Now, place your thumb tightly over the top of the straw |
| 4 | Thrust the straw forcefully into the potato |
| Observation | The straw pierces through the potato easily |
| Explanation | With thumb sealed, air inside straw is compressed and cannot escape; the rigid column of air pushes through |
D. Balloon in a Bottle 🎈
| Step | Procedure |
|---|---|
| 1 | Place a small balloon inside an empty plastic bottle, with its mouth stretched over the bottle opening |
| 2 | Try to blow up the balloon by blowing into the bottle |
| Observation | The balloon inflates only slightly |
| Explanation | Air already inside the bottle cannot escape; its pressure prevents balloon expansion |
16.1.3 Air Pressure and Altitude
| Altitude | Air Pressure | Effect |
|---|---|---|
| Sea level | 1013 millibars (highest) | Normal breathing |
| 1,000 m | ~899 mb | Slightly reduced |
| 3,000 m | ~701 mb | Some people feel breathless |
| 5,500 m | ~505 mb | Mountaineers need oxygen |
| 10,000 m | ~265 mb | Aircraft cabins must be pressurized |
📝 PSTET Note: Air pressure decreases with increasing altitude because there is less air above pressing down.
16.1.4 Air Pressure and Winds
Wind is caused by differences in air pressure:
High Pressure Area → Air moves → Low Pressure Area = WIND
| Pressure Difference | Wind Speed |
|---|---|
| Small difference | Gentle breeze |
| Large difference | Strong wind/storm |
| Extreme difference | Hurricane/cyclone force winds |
The Rule: Air always moves from high pressure areas to low pressure areas, just like water flows from higher to lower ground.
16.1.5 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Demonstration Stations | Set up 4-5 air pressure experiments for students to rotate through | Hands-on learning |
| "Why?" Discussion | After each demo, ask students to explain observations in their own words | Conceptual understanding |
| Everyday Connections | Discuss why straws work, why suction cups stick, why airplanes fly | Real-world application |
| Barometer Making | Create simple barometers using jars and balloons | Extended activity |
Section 16.2: High Speed Winds and Reduced Pressure (Bernoulli's Principle) ✈️
Introduction
Have you ever wondered why a roof blows off during a storm—not from inside, but from outside? Or how an airplane as heavy as a truck can fly? The answer lies in a fascinating relationship between the speed of a fluid (air or water) and the pressure it exerts .
16.2.1 What is Bernoulli's Principle?
Definition: Bernoulli's principle states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases .
Stated Simply:
Faster moving air = Lower pressure
Slower moving air = Higher pressure
The Principle in Equation Form (for reference only):
P + ½ρv² + ρgh = constant
Where:
P = Pressure
ρ (rho) = Density of fluid
v = Velocity (speed)
g = Acceleration due to gravity
h = Height
16.2.2 Simple Demonstrations of Bernoulli's Principle
These demonstrations are essential for classroom teaching and help students grasp this seemingly complex concept .
A. The Floating Paper Strip 📄
| Step | Procedure |
|---|---|
| 1 | Take a strip of paper about 20 cm long and 5 cm wide |
| 2 | Hold one end just below your lower lip |
| 3 | Blow strongly over the top surface of the paper |
| Observation | The paper rises instead of being pushed down |
| Explanation | Fast-moving air above creates low pressure; higher pressure below pushes paper up |
B. Two Balloons or Ping Pong Balls 🏓
| Step | Procedure |
|---|---|
| 1 | Suspend two balloons (or ping pong balls) about 5 cm apart |
| 2 | Blow strongly between them |
| Observation | The balloons move toward each other, not away |
| Explanation | Fast-moving air between them creates low pressure; higher pressure on outsides pushes them together |
C. The Spray Gun Effect 💦
| Step | Procedure |
|---|---|
| 1 | Take a glass of water and a straw |
| 2 | Hold another straw horizontally and blow across its top |
| 3 | Place the vertical straw in water and position it near the blowing straw |
| Observation | Water rises up the vertical straw and sprays out |
| Explanation | Fast-moving air across the top creates low pressure; atmospheric pressure pushes water up the straw |
D. Paper Between Books 📚
| Step | Procedure |
|---|---|
| 1 | Place two heavy books about 10 cm apart |
| 2 | Lay a sheet of paper across the gap between them |
| 3 | Blow strongly underneath the paper |
| Observation | The paper bends downward, not upward |
| Explanation | Fast-moving air under the paper creates low pressure; higher pressure above pushes paper down |
16.2.3 Real-Life Applications of Bernoulli's Principle
A. Airplane Wing (Aerofoil Lift) ✈️
How It Works:
The wing is designed with a curved upper surface and flatter lower surface
Air moving over the curved top must travel faster than air moving underneath
Faster air above = Lower pressure above the wing
Slower air below = Higher pressure below the wing
Table 16.2: Wing Pressure Comparison
| Location | Air Speed | Air Pressure | Effect |
|---|---|---|---|
| Above wing | Faster | Lower | Pulls wing up |
| Below wing | Slower | Higher | Pushes wing up |
📝 PSTET Note: While Bernoulli's principle explains lift, some physics teachers prefer using Newton's laws (angle of attack, air deflection). Both explanations are valid and complementary .
B. Blown-off Roofs During Storms 🏠
The Danger:
During a cyclone or strong storm, wind blows rapidly over the roof
Faster air above roof = Lower pressure above
Higher pressure inside the house (still air) pushes upward
Result: Roof lifts off—sometimes explosively!
Why This Matters:
This is why cyclone safety guidelines recommend opening windows slightly on the side opposite the wind—to equalize pressure and prevent the roof from blowing off .
C. Curving Balls in Sports ⚽
How It Works:
When a ball spins while moving through air, it drags air around with it
On one side, air moves faster (same direction as spin)
On the opposite side, air moves slower (opposite direction to spin)
Pressure difference causes the ball to curve
Examples:
Cricket: Swing bowling (reverse swing)
Football: Bending free kicks (like Beckham)
Tennis: Topspin and slice shots
D. Venturi Effect in Carburetors 🚗
In older car engines, a narrow constriction (venturi) in the air intake causes air to speed up, creating low pressure that draws fuel into the airstream.
E. Chimney and Smoke Draft
Wind blowing across the top of a chimney creates low pressure, drawing smoke up and out.
16.2.4 Bernoulli's Principle and Storms
Understanding Bernoulli's principle helps explain why storms are so destructive:
| Storm Effect | Bernoulli Explanation |
|---|---|
| Roof damage | High-speed wind outside creates low pressure; higher inside pressure lifts roof |
| Trees uprooted | Wind creates pressure differences around trees |
| Windows blown out | Pressure differential can shatter glass |
| Debris flying | Low-pressure areas behind objects can lift and carry them |
16.2.5 Pedagogical Implications
Section 16.3: Formation of Thunderstorms and Cyclones ⛈️
Introduction
Thunderstorms and cyclones are powerful weather systems that affect millions of people worldwide. Understanding how they form helps us predict them and stay safe .
16.3.1 Thunderstorm Formation
A. The Three Essential Ingredients
All thunderstorms require three basic ingredients :
| Ingredient | Description | Source |
|---|---|---|
| Moisture | Water vapor in the air | Oceans, large lakes, evaporation |
| Unstable Air | Warm, moist air near ground; cold, dry air above | Surface heating, weather fronts |
| Lift | Force that pushes air upward | Mountains, fronts, converging winds |
B. The Four Stages of Thunderstorm Development
Stage 1: Cumulus Stage ☁️
| Process | Description |
|---|---|
| 1 | Sun heats the ground, warming the air above |
| 2 | Warm, moist air rises (updraft) |
| 3 | As air rises, it cools and condenses into cumulus clouds |
| 4 | Rising air continues to feed the cloud |
Stage 2: Mature Stage 🌧️
Stage 3: Dissipating Stage 🌤️
| Process | Description |
|---|---|
| 1 | Downdrafts dominate; updrafts weaken |
| 2 | Moisture supply cut off |
| 3 | Storm runs out of energy |
| 4 | Rain becomes lighter, cloud dissipates |
Table 16.3: Thunderstorm Life Cycle
| Stage | Duration | Updrafts/Downdrafts | Weather |
|---|---|---|---|
| Cumulus | 10-15 minutes | Updrafts only | Building clouds |
| Mature | 20-30 minutes | Both updrafts and downdrafts | Heavy rain, lightning, hail, strong winds |
| Dissipating | 15-30 minutes | Downdrafts only | Light rain, clearing |
📝 PSTET Note: A single cumulonimbus cloud typically takes about an hour to form, mature, and dissipate. Longer-lasting storms involve multiple clouds forming in succession .
16.3.2 Cyclone Formation
Cyclones (called hurricanes in the Atlantic, typhoons in the Pacific) are the most powerful storms on Earth .
A. Essential Ingredients for Cyclone Formation
According to the Australian Bureau of Meteorology, cyclones need four main ingredients :
B. Why Cyclones Don't Form at the Equator
The Coriolis effect (caused by Earth's rotation) is weakest at the equator. Cyclones typically don't form within about 500 km (300 miles) of the equator because there isn't enough spin to organize the storm .
C. Stages of Cyclone Development
Meteorologists divide cyclone development into four stages :
Stage 1: Tropical Disturbance
Stage 2: Tropical Depression
Stage 3: Tropical Storm
Stage 4: Cyclone/Hurricane/Typhoon
| Process | Description |
|---|---|
| 1 | Wind speeds exceed 74 mph (119 km/h) |
| 2 | Well-defined eye forms (5-30 miles wide) |
| 3 | Eye wall contains strongest winds and heaviest rain |
| 4 | Storm can be 125+ miles across, 50,000+ feet high |
16.3.3 Anatomy of a Cyclone
Table 16.4: Parts of a Cyclone
16.3.4 Cyclone Intensity Scales
A. Saffir-Simpson Hurricane Wind Scale (Used in Atlantic/Eastern Pacific)
| Category | Wind Speed (km/h) | Wind Speed (mph) | Damage |
|---|---|---|---|
| 1 | 119-153 | 74-95 | Minimal |
| 2 | 154-177 | 96-110 | Moderate |
| 3 | 178-208 | 111-129 | Extensive |
| 4 | 209-251 | 130-156 | Extreme |
| 5 | ≥252 | ≥157 | Catastrophic |
B. Australian Tropical Cyclone Intensity Scale
| Category | Wind Gusts (km/h) | Description |
|---|---|---|
| 1 | <125 | Minor damage |
| 2 | 125-164 | Significant damage |
| 3 | 165-224 | Severe damage |
| 4 | 225-279 | Significant structural damage |
| 5 | >280 | Catastrophic destruction |
📝 PSTET Note: Category alone doesn't tell the full story. A Category 1 cyclone can cause worse flooding than a Category 5 if it brings more rain .
16.3.5 Cyclones in the Indian Context
India is highly vulnerable to cyclones due to its long coastline of 7,516 km .
Why Bay of Bengal has more cyclones:
Warmer sea surface temperatures
Higher moisture content
More favorable wind patterns
16.3.6 Hazards Associated with Cyclones
Storm Surge Explained:
Storm surge is often the deadliest part of a cyclone. The combination of:
Low pressure (allows sea level to rise)
Strong winds pushing water toward shore
Timing with high tide
can push water kilometers inland, destroying everything in its path .
16.3.7 Pedagogical Implications
Section 16.4: Safety Measures during Cyclones 🛡️
Introduction
India is one of the most cyclone-prone countries in the world. Knowing what to do before, during, and after a cyclone can save lives. The National Institute of Disaster Management (NIDM) and state governments provide detailed safety guidelines .
16.4.1 Before Cyclone Season (Preparedness)
Table 16.5: Pre-Season Preparations
16.4.2 When Cyclone Alert is Issued
16.4.3 When Cyclone Warning is Issued (Danger Imminent)
A. If You Are in a Vulnerable Area
| Action | Details |
|---|---|
| Leave low-lying areas | Get away from beaches and flood-prone zones |
| Go to high ground or shelter | Move before routes get flooded |
| Do not delay | Risk being marooned if you wait |
B. If Staying in a Safe House
C. Understanding the Eye of the Cyclone
Important Safety Rule:
If the center (eye) of the cyclone passes directly over your area, there will be a lull in wind and rain lasting half an hour or so .
16.4.4 When Evacuation is Instructed
16.4.5 During the Cyclone
| Action | Rationale |
|---|---|
| Stay indoors | Most dangerous place is outside with flying debris |
| Stay in strongest part of house | Interior room, bathroom, or corridor |
| Keep away from windows | Glass can shatter |
| Lie under sturdy table | Protection from debris |
| Listen to radio for updates | Stay informed on battery-powered radio |
| Do not use landline phone | Lightning risk |
16.4.6 Post-Cyclone Safety Measures
16.4.7 Cyclone Safety: Do's and Don'ts Summary Table
16.4.8 India's Cyclone Preparedness
📝 PSTET Note: Strict implementation of Coastal Zone Regulations, efficient early warning systems, and construction of cyclone shelters are key mitigation measures .
16.4.9 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Safety Poster Project | Students create posters illustrating do's and don'ts | Creative learning |
| Mock Drill | Practice evacuation drill in school | Life skills |
| Family Safety Plan | Students develop cyclone plan with their families | Community engagement |
| Case Study Analysis | Study recent cyclones (Amphan, Fani, etc.) and response | Critical thinking |
Chapter Summary: Key Points for Revision 📝
Quick Revision Table
| Topic | Key Points | Common PSTET Questions |
|---|---|---|
| Air Pressure | Air has weight and exerts pressure in all directions; decreases with altitude | Demonstrate air pressure with an experiment |
| Bernoulli's Principle | Faster moving air = lower pressure; explains lift, roof damage, curve balls | Why do roofs blow off during storms? |
| Thunderstorm Formation | Needs: moisture, unstable air, lift; 3 stages: cumulus, mature, dissipating | What causes thunderstorms? |
| Cyclone Formation | Needs: warm ocean (≥26.5°C), low pressure, Coriolis effect; 4 stages of development | Why don't cyclones form at the equator? |
| Cyclone Parts | Eye (calm), Eye wall (most dangerous), Rainbands | What is the eye of a cyclone? |
| Cyclone Categories | Category 1-5 based on wind speed; Category 5 most destructive | What are cyclone categories? |
| Cyclone Hazards | High winds, storm surge (deadliest), heavy rain, flooding | What is a storm surge? |
| Before Cyclone | Secure house, stock supplies, identify shelter | What preparations should you make? |
| During Cyclone | Stay indoors, board windows, switch off mains | What to do during cyclone? |
| After Cyclone | Stay in shelter until informed, avoid wires, get vaccinated | Post-cyclone safety measures |
Practice Zone: PSTET-Style Questions 🎯
Content-Based MCQs
Q1. According to Bernoulli's principle, when the speed of a fluid increases, its pressure:
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
Q2. Which of the following is NOT required for thunderstorm formation?
a) Moisture
b) Unstable air
c) Cold ocean water
d) Lift mechanism
Q3. The most dangerous part of a cyclone is the:
a) Eye
b) Eye wall
c) Rainbands
d) Outflow
Q4. Cyclones do not form near the equator because:
a) Water is too cold
b) Coriolis effect is too weak
c) Winds are too strong
d) Air is too dry
Q5. During a cyclone, if there is a sudden calm with no wind or rain, this means:
a) The cyclone is over
b) The eye is passing over; strong winds will return from opposite direction
c) It's safe to go outside
d) The cyclone has weakened
Q6. The instrument used to measure atmospheric pressure is called a:
a) Thermometer
b) Barometer
c) Anemometer
d) Hygrometer
Q7. Which ocean basin experiences more cyclones affecting India?
a) Arabian Sea
b) Bay of Bengal
c) Indian Ocean (southern)
d) Pacific Ocean
Q8. The minimum ocean temperature required for cyclone formation is:
a) 20°C
b) 23°C
c) 26.5°C
d) 30°C
Q9. Storm surge is caused by:
a) Heavy rain only
b) Combination of low pressure, strong winds, and tides
c) Underwater earthquakes
d) River flooding
Q10. According to safety guidelines, during the lull (eye) of a cyclone, you should:
a) Go outside to check damage
b) Stay inside because winds will return
c) Open all windows
d) Drive to a safer location
Pedagogical MCQs
Q11. A teacher wants to demonstrate Bernoulli's principle. The most effective demonstration would be:
a) Show a diagram of an airplane wing
b) Have students blow between two hanging balloons and observe them move together
c) Lecture about the principle
d) Show a video of a hurricane
Q12. To help students understand why cyclones don't form at the equator, the teacher should:
a) Show a map and explain Coriolis effect
b) Have students spin a ball with water on it
c) Give a definition to memorize
d) Skip this concept as too difficult
Q13. A student asks, "Why do we need to board up windows during a cyclone?" The best explanation is:
a) "To keep rain out"
b) "To prevent windows from breaking due to wind pressure and flying debris"
c) "Because the government says so"
d) "To keep the house dark"
Q14. While teaching cyclone safety, the most effective approach is:
a) Give students a list to memorize
b) Conduct a mock drill in the school
c) Show pictures of cyclone damage
d) Read from textbook
Q15. A teacher demonstrates the can-crushing experiment. This demonstrates:
a) Bernoulli's principle
b) That air exerts pressure
c) Cyclone formation
d) Evaporation
Answer Key with Explanations
Pedagogical Reflection for Teachers 🤔
Think-Pair-Share Activity:
Think: How would you explain to students why it's dangerous to go outside during the calm (eye) of a cyclone?
Pair: Discuss with a colleague how you would develop a "Cyclone Safety Plan" for your school.
Share: Design a 15-minute activity to teach Bernoulli's principle using simple materials available in any classroom.
NCERT Textbook Linkages 📚
| Class | Chapter | Topic |
|---|---|---|
| Class 7 | Chapter 8 | Winds, Storms and Cyclones |
| Class 9 | Chapter 14 | Natural Resources |
| Class 11 | Chapter 10 | Atmospheric Circulation and Weather Systems |
Chapter End Notes
Key Terminology Glossary
Quick Tips for PSTET Aspirants ⚡
✅ Memorize with Mnemonics:
Cyclone Ingredients: "Warm Water, Low Pressure, Coriolis, Thunderstorms" = W W L C T
Thunderstorm Stages: "Cumulus, Mature, Dissipating" = C M D
Cyclone Stages: "Disturbance, Depression, Storm, Cyclone" = D D S C
Cyclone Safety: "Before—Prepare, During—Inside, After—Wait" = B D A
✅ Common Exam Traps:
Eye is CALM, not dangerous—but eye wall is MOST dangerous
Coriolis effect is ZERO at equator—cyclones don't form there
Storm surge is often deadlier than wind
Lull (eye) is temporary—NEVER go outside during it
Cyclone categories don't tell full story—a Category 1 can cause worse flooding than Category 5
Bernoulli's principle explains lift, but angle of attack also matters
✅ Important Facts:
Answers to "Check Your Understanding"
[To be filled by student]
📝 Note for Self-Study: After completing this chapter, ensure you can:
Perform and explain 3 air pressure demonstrations
State Bernoulli's principle and give 4 real-life examples
List the three ingredients for thunderstorm formation
Describe the three stages of thunderstorm development
List the four ingredients for cyclone formation
Explain why cyclones don't form at the equator
Describe the four stages of cyclone development
Label the parts of a cyclone (eye, eye wall, rainbands)
List 5 things to do BEFORE a cyclone
List 5 things to do DURING a cyclone
List 5 things to do AFTER a cyclone
Explain why you should NEVER go outside during the lull
