CLASS 7 SOCIAL SCIENCE · PART 1 · CHAPTER 2 · STUDY NOTES
Understanding the Weather
Measure weather, compare readings and use forecasts thoughtfully.
01 / EXPLORE & UNDERSTAND
Weather happens in the air around us
Weather always belongs to a place and a time.
Weather is mainly in the lowest layer
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1. Start with what you notice
A cloudy morning can become a sunny afternoon. “Hot”, “windy” and “rainy” describe parts of the weather, but one word rarely tells the whole story. Add the place and observation time.
2. Locate the weather layer
The atmosphere is the layer of gases around Earth. Almost all familiar weather occurs in its lowest layer, the troposphere. Its thickness varies; the diagram’s curved layers are a simplified model, not solid shells.
Your turn
Question
Why is “It is raining” an incomplete weather report?
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02 / EXPLORE & UNDERSTAND
Five measurements build a weather picture
Weather is a combination of conditions, not just temperature.
1. Ask five questions
How hot is the air? What precipitation falls? What is the air pressure? How fast and from where does wind blow? How much water vapour is present? These questions correspond to temperature, precipitation, pressure, wind and humidity.
2. Use numbers for comparison
Two people may disagree about whether 20°C feels cold. A thermometer reading gives them a common measurement. Use standard units and consistent methods so readings from different places can be compared.
Your turn
Question
Can two days at 28°C feel different? Explain.
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03 / EXPLORE & UNDERSTAND
Nature gives clues, not guaranteed forecasts
Observation is valuable when we also test how reliable it is.
Compare the open and closed cone
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1. Respect observations
Communities have long noticed changes in animal behaviour, plants and clouds. Pine cones, for example, open or close as humidity changes. These observations can raise useful questions about the environment.
2. Check a claim against records
A frog calling does not guarantee rain tomorrow. Keep dated observations and compare them with measured weather. Modern forecasts combine many measurements and models rather than relying on one sign.
Your turn
Question
How could you test a local saying that predicts rain?
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04 / EXPLORE & UNDERSTAND
Measure the air, not your feeling
A useful reading needs a suitable instrument and location.
Two readings, two different answers
Range measures the spread. The midpoint gives a simple estimate of the daily mean.
- Daily range
- 32 − 18 = 14°C
- Estimated mean
- (32 + 18) ÷ 2 = 25°C
1. Match instrument and unit
A thermometer measures temperature. Weather reports commonly use degrees Celsius (°C). A maximum–minimum thermometer records the highest and lowest values over a period. Digital sensors can record many readings automatically.
2. Avoid a misleading position
A thermometer in direct sunshine may become hotter than the surrounding air. Weather stations use suitable protection and ventilation. Comparing an exposed wall reading with a shaded station reading may compare different conditions.
Your turn
Question
Why should a weather thermometer not simply sit in direct sunshine?
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05 / EXPLORE & UNDERSTAND
Range and mean answer different questions
Use the same day’s maximum and minimum for both calculations.
Two readings, two different answers
Range measures the spread. The midpoint gives a simple estimate of the daily mean.
- Daily range
- 32 − 18 = 14°C
- Estimated mean
- (32 + 18) ÷ 2 = 25°C
1. Find how much it varied
In an invented example, the maximum is 34°C and the minimum is 22°C. The range is 34 − 22 = 12°C. This describes the difference between the extremes, not the temperature at noon.
2. Find the textbook mean
Using the chapter’s method, mean daily temperature is (maximum + minimum) ÷ 2. Here, (34 + 22) ÷ 2 = 28°C. Brackets matter: add first, then divide. This estimate need not equal an average of every hourly reading.
A little deeper: Same mean, different experience
Days with 34/22°C and 30/26°C both have a mean of 28°C, but ranges of 12°C and 4°C. A mean alone hides how much temperatures changed.
Your turn
Question
A day has maximum 31°C and minimum 19°C. Find range and the textbook mean.
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06 / EXPLORE & UNDERSTAND
Rainfall is reported as a depth
Millimetres of rain describe an amount, not the size of raindrops.
Opening, funnel and measuring tube
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How much rain fell?
Keep the collected water the same. Now change the size of the opening.
15.0 mm = 150 mL ÷ 100 cm² × 10. Same volume through a larger opening means a smaller rainfall depth.
1. Read the meaning of millimetres
A rainfall total of 10 mm means enough water to make a 10 mm deep layer on level ground if none ran off, soaked in or evaporated. Over one square metre, that equals 10 litres. It does not mean puddles everywhere are 10 mm deep.
2. Read a calibrated gauge
A rain gauge collects water through an opening. Its scale must account for the opening and collecting tube sizes. If a wide funnel feeds a narrow tube, raw water depth in the tube is not automatically the rainfall depth.
Your turn
Question
Does 15 mm rainfall describe the diameter of a raindrop?
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07 / EXPLORE & UNDERSTAND
Good measurements need a fair setup
A correct instrument in a poor position can still give poor data.
How much rain fell?
Keep the collected water the same. Now change the size of the opening.
15.0 mm = 150 mL ÷ 100 cm² × 10. Same volume through a larger opening means a smaller rainfall depth.
1. Choose the site
Use a stable, level, open location with the teacher’s help. Keep away from roofs, trees and splash water. Shelter can stop rain entering, while runoff from a roof can add water that did not fall directly into the gauge.
2. Keep a consistent record
Read at the same time each day and record the units and interval. Follow the instrument’s instructions for emptying and resetting. In an invented three-day record of 4, 0 and 8 mm, the total is 12 mm and daily mean is 4 mm.
Your turn
Question
Why is a spot directly under a roof edge unsuitable?
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08 / EXPLORE & UNDERSTAND
Air exerts pressure
Air is invisible, but its pressure can be measured.
1. Compare low and high ground
Pressure generally decreases as height increases because less air lies above. A barometer measures pressure, commonly in millibars or hectopascals: 1 mb = 1 hPa. About 1013 hPa is a standard sea-level reference, not a fixed value everywhere.
2. Separate altitude from a weather system
A low reading on a mountain does not by itself prove a storm is coming. Meteorologists compare patterns and changes, often adjusting pressure to a common reference level. A low-pressure system is lower than its surroundings, not simply any reading below one number.
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Question
Would 900 hPa at a high mountain station alone prove a cyclone?
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09 / EXPLORE & UNDERSTAND
Wind needs both a speed and a direction
The name of a wind tells us where it comes from.
Direction on the left, speed on the right
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1. Read the direction correctly
A west wind blows from the west towards the east. A wind vane points into the wind. A windsock’s open mouth faces the incoming wind while its tail extends downwind. These are different shapes that show related information.
2. Measure speed separately
A cup anemometer measures wind speed from its rotation rate. Its cups alone do not tell direction. Pressure differences help drive wind; Earth’s rotation and friction also affect its actual path. Wind data helps pilots, sailors and farmers plan.
Your turn
Question
A report says “north wind”. Towards which direction does it blow?
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10 / EXPLORE & UNDERSTAND
Humidity describes invisible water vapour
Humid air is not the same thing as falling rain.
1. Read the percentage
A hygrometer measures humidity. A reading of 80% relative humidity does not mean 80% of the air is water. It means the vapour level is close to saturation for that temperature. The percentage can change when temperature changes even without adding water.
2. Connect it with drying
With other conditions equal, wet clothes usually dry faster at lower relative humidity. In humid air, evaporation is slower. Sweat that evaporates cools the body; sweat remaining on the skin does not provide the same cooling.
A little deeper: Humidity needs control, not always dryness
Food processing and museums monitor humidity. Different materials need suitable ranges: excessive dryness can also damage some objects. The aim is controlled conditions, not simply the driest possible air.
Your turn
Question
Does 70% relative humidity mean rain covers 70% of the city?
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11 / EXPLORE & UNDERSTAND
A station gathers many kinds of evidence
Several instruments work together at one observation site.
Sensors work together
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1. Match sensors to questions
Temperature, rain, pressure, wind and humidity need different sensors. Readings taken at regular times reveal changes that a single observation might miss. Automation makes frequent and remote measurements possible.
2. Remember human responsibility
Automatic does not mean error-free or maintenance-free. Sensors need correct placement, calibration, power and checks. A broken rain sensor can report zero even when rain falls, so unusual data must be investigated.
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Question
Why might regular hourly readings be more useful than one reading in a day?
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12 / EXPLORE & UNDERSTAND
A forecast helps people prepare
A forecast is an evidence-based prediction, not a guarantee.
1. Turn observations into a prediction
Meteorologists combine measurements from many places with scientific models. They update forecasts as new observations arrive. A forecast should say where, when and what is expected, and communicate uncertainty.
2. Connect information to a decision
A school can change an outdoor event, fishers can follow a sea warning, and authorities can prepare shelters before dangerous weather. Forecasts reduce surprise, but good communication and timely action are also needed.
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Question
Why should an old forecast not be treated as the final word?
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13 / EXPLORE & UNDERSTAND
Read the date, colour and symbol together
The textbook warning map is a historical example, not today’s forecast.
Historical example: 19 May 2024
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1. Check the message
The sample map is dated 19 May 2024. Its colours mean: green—no warning shown; yellow—stay updated; orange—be prepared; red—take action. Follow the actual advisory for the named place and period rather than guessing from a colour alone.
2. Identify the weather hazard
A symbol identifies the expected condition, such as rain or a heat wave. Red does not mean “hot” and green does not promise perfect weather. Weather tables also need units: rain may be in millimetres while snowfall is shown in centimetres.
A little deeper: A reading needs a place and time
A temperature without a place, time and unit tells only part of the story. Compare readings taken in similar conditions. A forecast describes what may happen; an observation records what was measured.
Your turn
Question
A map has a red area and a rain symbol. Does the red mean high temperature?
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Sign inNew here? Sign up freeCHAPTER RECAP
Take these ideas with you
- Weather describes a place and time.
- Temperature, precipitation, pressure, wind and humidity work together.
- Range = maximum − minimum; textbook daily mean = (maximum + minimum) ÷ 2.
- A cup anemometer measures speed; a wind vane shows where wind comes from.
- Relative humidity is not the percentage of air made of water.
- Use a current forecast’s place, time, hazard and advice.
Use your understanding in a new situation
Question
A maximum of 29°C and minimum of 17°C are recorded. Give the range and textbook mean.
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Name the instruments for rainfall, pressure and humidity.
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Sign inNew here? Sign up freeNCERT · Chapter source PDF, pages 14, 15, 17 · Original Learnijoy explanations and practice.