This MCQ module is based on: Measuring & Predicting Weather
TOPIC 5 OF 42
Measuring & Predicting Weather
🎓 Class 7
Social Science
CBSE
Theory
Ch 2 — Understanding the Weather
⏱ ~15 min
🌐 Language: [gtranslate]
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[myaischool_lt_sst_assessment grade_level="class_7" subject="geography" difficulty="basic"]
Measuring & Predicting Weather
NCERT Social Science — Exploring Society: India and Beyond | Grade 7 Part I
Measuring Atmospheric Pressure
Your body naturally senses temperature and rain, but you may also have noticed that the weather sometimes feels "heavy" — especially before a thunderstorm. This sensation is linked to atmospheric pressure?, which is the force exerted by the weight of the air above and around us on the Earth's surface.
Atmospheric pressure is higher near the coast (at sea level) and decreases as altitude increases. When you climb a mountain, the air becomes thinner — meaning there is less air pressing down and less oxygen available. This is why people sometimes feel breathless, dizzy, or tired at high altitudes. The body has to work harder to function with reduced oxygen.
Definition
Acclimatise: To adjust gradually to a new climate or condition — particularly to lower oxygen levels at high altitudes.
Low atmospheric pressure in the plains or on the coast does not always stay constant. Sometimes it drops sharply, creating what meteorologists call a depression or low-pressure system. If conditions intensify, this can develop into a storm or even a cyclone?.
THINK ABOUT IT — Why Measure Atmospheric Pressure?
L4 Analyse
Why do you think it would be important to measure atmospheric pressure? Who are the people most likely to use such measurements in their work?
Guidance
Atmospheric pressure readings are crucial for weather forecasting — a sudden drop often signals approaching storms. Pilots depend on barometric data for safe take-offs and landings. Sailors and fishermen use pressure readings to anticipate storms at sea. Mountain climbers and the military posted at high altitudes track pressure to manage health risks due to low oxygen.
The instrument used to measure atmospheric pressure is called a barometer?. The standard unit is the millibar (mb). Normal atmospheric pressure at sea level is approximately 1013 mb. A reading below 1000 mb usually indicates a depression that could bring unsettled weather.
THINK ABOUT IT — Life at Extreme Altitudes
L4 Analyse
Travellers to high-altitude places are advised to pause along the way so the body can acclimatise. Indian army personnel serve at places like Khardung La in Ladakh, over 5,600 metres above sea level, where the atmospheric pressure is only about 650 millibars. Reflect on the immense challenges these soldiers face living and working where oxygen is so scarce.
Guidance
At 650 mb, the air has roughly 35% less oxygen than at sea level. Soldiers must gradually acclimatise over days or weeks. They face risks of altitude sickness, frostbite, and fatigue. Cooking takes longer because water boils at a lower temperature. Equipment must be specially designed for extreme cold. Their service at such posts is a remarkable feat of endurance and dedication.
Measuring Wind — Speed and Direction
Wind? is the movement of air from areas of high pressure towards areas of low pressure. Two important factors describe wind: its speed (how fast it moves) and its direction (where it comes from).
Wind plays a vital role in weather. Its direction and speed help in forecasting. Pilots and sailors need wind data because wind greatly affects flying and navigation. Farmers use wind direction to predict where rain might come from, and stronger winds cause soil to dry faster.
THINK ABOUT IT — Seeds in the Wind
L4 Analyse
Many plants produce seeds with wing-like structures that catch the wind and fly great distances. What would happen to these seeds if there were no wind? How would this affect the spread of forests and plant species?
Guidance
Without wind, these seeds would simply fall near the parent plant. Over time, this would lead to overcrowding and intense competition for sunlight, water, and nutrients. Wind dispersal allows seeds to colonise new areas, increasing biodiversity and enabling forests to regenerate after fires or droughts. Wind is thus essential for the ecological health of plant communities.
Instruments for Measuring Wind
Wind Vane (Weather Vane)
A rotating arm with a pointer at one end and a tail at the other. When wind blows, the tail pushes and the pointer turns to show the wind's direction. Responds even to a light breeze.
Wind Sock
A cone-shaped fabric tube on airport tarmacs. It indicates wind direction and gives pilots visual cues for take-off and landing. Also used near factories that release ash or gases.
Anemometer
Has three or four metal cups on a vertical shaft. Wind makes the cups spin — the stronger the wind, the faster the rotation. A meter at the bottom calculates speed in km/h.
Measuring Humidity
Humidity? is the amount of water vapour present in the air. It depends on factors like temperature, wind, atmospheric pressure, and location (proximity to water bodies).
LET'S EXPLORE — Comparing Humidity
L3 Apply
Where do you think humidity would be higher — Kochi or Jaipur? You might guess Kochi because it is near the sea. But how would we know for certain? And if we had to compare humidity between Kochi and Mangaluru (both coastal), how would we do it? Discuss with your classmates.
Guidance
While common sense tells us coastal Kochi is more humid than desert-side Jaipur, we need instruments (hygrometers) to measure exact numbers. Comparing two coastal cities like Kochi and Mangaluru requires precise readings because other factors (local winds, ocean currents, vegetation) also affect humidity. Data-driven measurement removes guesswork.
Humidity is expressed as relative humidity?. Air with no water vapour at all would be 0% (practically impossible in nature), while air completely saturated with moisture would be 100%. In practice, dry weather has relative humidity between 20% and 40%, while humid weather usually falls between 60% and 80%.
Science Connection
Recall from Grade 6 Science: when water evaporates, it causes a cooling effect. If the air already contains a lot of moisture (high humidity), evaporation happens slowly — which is why rainy days feel clammy and uncomfortable.
THINK ABOUT IT — Drying Clothes and Sweating
L4 Analyse
If Delhi has 52% humidity while Kochi has 84% humidity, in which city would wet clothes dry faster? And where are you more likely to sweat more, assuming the temperature is the same in both places?
Guidance
Clothes would dry faster in Delhi because lower humidity means the air can absorb more moisture, allowing quicker evaporation. You would sweat more in Kochi because the high humidity slows evaporation from your skin. Since sweating cools the body through evaporation, when evaporation is slow, sweat accumulates and you feel hotter and stickier.
Humidity is measured using a hygrometer?. There are several types, each based on different scientific principles. Accurate humidity measurement is crucial in industries like food processing (to prevent spoilage) and in museums (to maintain a dry environment for preserving artefacts and exhibits).
Weather Stations and Automated Monitoring
Since measuring weather requires multiple instruments, a weather station? brings all these instruments together in one place. Readings are taken at regular intervals, which helps in mapping and forecasting the weather.
Definition
Automated Weather Station (AWS): A self-operating system that uses sensors to measure and record weather data — temperature, humidity, wind speed and direction, precipitation, and atmospheric pressure — without human intervention. Widely used in agriculture, aviation, navigation, and environmental monitoring.
DON'T MISS OUT — AWS at 4,800 Metres
L2 Understand
In 2023, the National Disaster Management Authority (NDMA) installed an Automated Weather Station at a glacial lake in Sikkim, at an altitude exceeding 4,800 metres above sea level. This AWS provides early information about approaching weather conditions, helping authorities prepare for potential glacial lake outburst floods (GLOFs) and other extreme weather events in this ecologically sensitive Himalayan region.
Predicting the Weather
Meteorologists collect data from weather stations over long periods and use scientific methods to predict weather. These predictions have become increasingly vital as climate change makes extreme weather — droughts, floods, cyclones, and heat waves — more frequent and intense.
Accurate forecasts enable local governments to mobilise resources and prepare for disasters. For instance, if stormy weather is expected at sea, fishermen are warned against venturing out. Entire coastal areas may need to be evacuated before a cyclone strikes.
LET'S EXPLORE — When Do Weather Predictions Help?
L3 Apply
Work in pairs. Discuss different situations in which weather predictions are helpful. After making your list, share it with the pair sitting next to you. How many different categories of situations were you able to identify?
Example Categories
Agriculture: Sowing, harvesting, irrigation planning. Transport: Air traffic, shipping, road safety. Disaster management: Cyclone evacuation, flood preparedness. Daily life: Deciding what to wear, planning outdoor events. Health: Heat wave advisories, cold wave alerts for the elderly. Industry: Construction schedules, energy demand forecasting.
LET'S EXPLORE — Reading an IMD Weather Warning Map
L4 Analyse
The India Meteorological Department issued a weather warning map for 19 May 2024. The map uses colour-coded warnings: Green (No Warning), Yellow (Watch — Be Updated), Orange (Alert — Be Prepared), and Red (Warning — Take Action). Study the weather icons and answer:
- What different weather conditions is the IMD alerting people to on that day?
- Which states have warning-level (red) alerts?
- Which parts of India appear to be free from severe weather?
- Which states are likely to face heat wave conditions?
- What is causing warnings in Tripura and Lakshadweep?
Guidance
The map shows multiple weather hazards occurring simultaneously across India — heat waves in northern and central states (Rajasthan, Gujarat, Madhya Pradesh), thunderstorms and lightning in the northeast, and heavy rain warnings in some coastal areas. Southern India and parts of the east might be relatively calm. This exercise shows how weather forecasting helps different regions prepare for their specific challenges at the same time.
Key Takeaways — Before We Move On
Five Elements Define Weather
Temperature, humidity, precipitation, wind, and atmospheric pressure together describe the weather at any given place and time.
Instruments Enable Precision
Thermometers, rain gauges, barometers, anemometers, and hygrometers provide accurate data that allows us to monitor and predict weather.
Dominant Elements Vary
In July, rainfall dominates. In May, temperature is key. During cyclones, atmospheric pressure is critical. During loo winds or forest fires, wind takes centre stage.
Weather Links to Climate
Weather is closely linked to climate — the long-term average weather pattern of a place. This connection will be explored in the next chapter.
Weather Elements & Their Instruments
L4 AnalyseFigure: Each weather element is measured by a specific instrument, with its own unit of measurement.
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Competency-Based Questions — Pressure, Wind, Humidity & Prediction
Case Study: A fishing village on the coast of Odisha receives an alert from the IMD that atmospheric pressure has dropped to 985 mb and a cyclonic depression is forming over the Bay of Bengal. Wind speeds of 80 km/h are expected within 48 hours. The village headman must decide what actions to take immediately.
Q1. What does an atmospheric pressure reading of 985 mb indicate?
L2 Understand
Answer: (B) — Normal sea-level pressure is about 1013 mb. A reading of 985 mb is well below 1000 mb, indicating a depression or low-pressure system that could intensify into a storm or cyclone.
Q2. Which instrument would the IMD primarily rely on to track the strengthening of this cyclonic system?
L3 Apply
Answer: (C) — The barometer tracks how rapidly pressure is falling (indicating strengthening), while the anemometer measures wind speed — the key factor in classifying the severity of a cyclone.
Q3. Explain why people at high altitudes like Khardung La often feel breathless and tired. How does atmospheric pressure relate to this? (2 marks)
L4 Analyse
Model Answer: At high altitudes, the atmospheric pressure is much lower (about 650 mb at Khardung La compared to 1013 mb at sea level). Lower pressure means the air is thinner, with significantly less oxygen per breath. The body's cells do not receive enough oxygen for normal functioning, so the heart and lungs must work harder. This leads to breathlessness, dizziness, and fatigue — symptoms known as altitude sickness. Gradual acclimatisation allows the body to adapt by producing more red blood cells.
HOT Q. You are the village headman in the case study. Draft a short emergency announcement (5-6 lines) for the village loudspeaker, warning residents about the approaching cyclone and listing three specific actions they must take immediately.
L6 Create
Hint: Include: (1) What is happening (cyclone approaching, strong winds expected), (2) When it will arrive (within 48 hours), (3) Actions — secure boats, move to designated shelters, stock essential supplies. Keep the language simple and urgent. Address the community directly.
🎯 Practice Questions — Pressure, Wind, Humidity & Prediction
True or False
1. Atmospheric pressure increases as we climb to higher altitudes.
FALSE
2. An anemometer measures wind speed by counting the rotations of its cups.
TRUE
3. Relative humidity of 100% means the air contains absolutely no water vapour.
FALSE
Corrections:
1. FALSE — Atmospheric pressure decreases with altitude because the column of air above gets thinner.
3. FALSE — 100% relative humidity means the air is fully saturated with water vapour, not that it has none. 0% would mean no water vapour.
1. FALSE — Atmospheric pressure decreases with altitude because the column of air above gets thinner.
3. FALSE — 100% relative humidity means the air is fully saturated with water vapour, not that it has none. 0% would mean no water vapour.
Match the Following
1. Barometer
?
(a) Wind speed
2. Hygrometer
?
(b) Atmospheric pressure
3. Anemometer
?
(c) Wind direction
4. Wind vane
?
(d) Humidity
Answers: 1 → (b), 2 → (d), 3 → (a), 4 → (c)
Think & Create
Imagine you are setting up a mini weather station in your school. Draw or describe the layout of your station. Which five instruments would you include, and where exactly would you place each one? Explain why placement matters for accurate readings.
Guidance
Include: thermometer (in shade, away from walls), rain gauge (open area, flat surface, away from trees), barometer (indoors or sheltered), anemometer (elevated, unobstructed spot), and hygrometer (sheltered from direct rain). Placement matters because surrounding objects, buildings, or shade can affect readings — for example, placing a thermometer in direct sunlight gives a falsely high reading.
Continue Learning — Chapter 2: Weather and Climate
- Previous: Part 1 — Weather and Its Elements
- Related: Chapter 3 — Climates of India
- Class 7 Social Science — All Chapters
External: Official NCERT Textbooks | CBSE Curriculum 2025
Frequently Asked Questions — Measuring Predicting Weather
What is a barometer and what does it measure?
A barometer is an instrument used to measure atmospheric pressure — the weight of air pressing down on the earth's surface. Pressure is measured in millibars (mb). Normal sea-level pressure is about 1013 mb. When pressure falls, it often signals approaching rain or storms; when it rises, fair weather is likely. The mercury barometer, invented by Evangelista Torricelli, uses a column of mercury in a glass tube. Modern aneroid barometers use a sealed metal chamber that expands and contracts with pressure changes.
How does an anemometer measure wind speed?
An anemometer measures wind speed using rotating cups mounted on a vertical axis. When wind blows, the cups spin — faster wind makes them spin more quickly. The number of rotations per unit time is converted into wind speed, usually expressed in kilometres per hour (km/h) or metres per second (m/s). At weather stations, anemometers are placed at a standard height of 10 metres above the ground to ensure consistent readings. Digital anemometers display readings electronically for quick reference.
What is the India Meteorological Department and what does it do?
The India Meteorological Department (IMD) is the national weather agency responsible for weather observation, forecasting, and issuing warnings across India. Founded in 1875 with headquarters in New Delhi, the IMD operates a vast network of weather stations, satellites, and radar systems. It provides daily weather forecasts, monsoon predictions, cyclone warnings, and climate data. IMD's forecasts help farmers plan agricultural activities, help disaster management authorities prepare for extreme weather, and assist aviation and shipping with safety information.
What is a hygrometer and why is humidity important?
A hygrometer is an instrument that measures humidity — the amount of water vapour present in the air. Humidity is expressed as a percentage called relative humidity. When relative humidity is 100%, the air is fully saturated and can hold no more moisture, often leading to precipitation. Humidity is important because it affects human comfort (high humidity makes hot days feel hotter), agriculture (plants need certain moisture levels), and weather prediction (rising humidity can signal approaching rain).
How do weather satellites help in forecasting?
Weather satellites orbit the earth and capture images of cloud patterns, storms, and temperature changes from space. They provide a bird's-eye view of weather systems that ground stations alone cannot see. Geostationary satellites stay fixed above one point and give continuous images, while polar-orbiting satellites circle the earth and scan different areas. This satellite data, combined with information from ground stations and radar, is fed into supercomputers that run mathematical weather models to generate forecasts.
What is the difference between weather stations and automated weather stations?
Traditional weather stations rely on trained observers who manually read instruments like thermometers, barometers, and rain gauges at fixed times each day. Automated weather stations (AWS) use electronic sensors to continuously record temperature, pressure, humidity, wind, and rainfall without human intervention. Data is transmitted automatically to central servers via satellite or internet. AWS can operate in remote or harsh locations where human observation is difficult, and they provide readings every few minutes rather than just a few times per day.
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Social Science Class 7 — Exploring Society Part I
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