Example 1: rainfall data
Rainfall in three months was 60, 180 and 90 mm. Find the mean.
- Total = 60 + 180 + 90 = 330 mm.
- Mean = 330 ÷ 3 = 110 mm.
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IB DemystifiedMYP Sciences
Weather and the water cycle
The water you drink today may once have fallen as monsoon rain, flowed down the Indus, or floated as a cloud over the Arabian Sea. The water cycle moves water endlessly between sea, air and land, and it shapes our weather.
Recommended for MYP 1 · About 3 lessons · Criteria A, B, C and D
On this page
- Learning objectives
- Before you start
- Key vocabulary
- Understanding the ideas
- Measuring the weather
- The water cycle in the real world
- Worked examples
- Assessment tips
- Check your understanding
- Practice questions
- Investigation
- Criterion-linked questions
- Challenge questions
- Topic check
- Review your mistakes
- Your progress
Learning objectives
By the end of this topic you should be able to:
- describe the processes of the water cycle
- explain evaporation and condensation using temperature and particles
- measure and describe the weather with instruments
- distinguish weather from climate and interpret rainfall data
- explain how people depend on and change the water cycle
- discuss flooding and water shortages
Before you start
You will use these skills. If any feel shaky, review them first.
- solids, liquids and gases (see States of matter)
- separating mixtures and distillation (see Pure substances, mixtures and separation)
- reading tables and calculating means
Key vocabulary
- Evaporation
- Liquid water turning into water vapour.
- Condensation
- Water vapour cooling and turning into liquid water.
- Precipitation
- Water falling from clouds as rain, snow, sleet or hail.
- Transpiration
- Water evaporating from plant leaves.
- Runoff
- Water flowing over the land into rivers and the sea.
- Climate
- The average weather in a place over many years.
Understanding the ideas
-
What is it?
Energy from the Sun makes water evaporate from seas, lakes and plants. The water vapour rises, cools and condenses into tiny droplets that form clouds. When droplets join and grow heavy, they fall as precipitation, then flow back to the sea as runoff or soak into the ground as groundwater.
-
Why does it happen?
Evaporation is faster when it is warm, windy and dry; condensation happens when water vapour cools. Because only water evaporates, rain is fresh water: the water cycle is nature's distillation.
-
How do we know?
Weather stations measure temperature, rainfall, wind speed and direction, and air pressure. Long-term records show the climate, such as the monsoon season in South Asia.
-
Why does it matter?
People depend on the water cycle for drinking water, farming and electricity, but floods, droughts and falling groundwater levels can cause serious problems.
-
What does it connect to?
This topic links to states of matter and distillation in chemistry, to transpiration in plants, and later to climate change.
Measuring the weather
- Thermometer: temperature (°C).
- Rain gauge: rainfall (mm).
- Anemometer: wind speed.
- Wind vane: wind direction.
- Barometer: air pressure; falling pressure often means wet, windy weather.
- Weather is day to day; climate is the average over about 30 years.
The water cycle in the real world
South Asia depends on the summer monsoon for most of its rain. Glaciers in the Himalayas and Karakoram store water that feeds rivers in summer. Many cities are building rainwater harvesting systems to refill groundwater.
Worked examples
Example 2: explaining a process
Why does a bathroom mirror mist up after a hot shower?
- Warm water evaporates, so the air contains lots of water vapour.
- The vapour touches the cool mirror, cools and condenses into tiny droplets.
Assessment tips
Questions on the water cycle often use diagrams and weather data. Expect to:
- Describe the water cycle using the correct words.
- Explain evaporation and condensation.
- Process rainfall and weather data.
- Discuss floods and water supply.
Common mistakes: saying clouds are water vapour (they are droplets); mixing up evaporation and condensation; confusing weather with climate; and trusting a mean without looking at how the data vary.
Check your understanding
Quick questions on the ideas above. Try each one before using a hint.
Practice questions
Investigation: a water cycle in a bowl
Partially guided investigation · about 40 minutes · pairs
- Research question
- Can a sealed model show evaporation, condensation and precipitation, and does warmer water make it happen faster?
- Scientific background
- Warm water evaporates; when the vapour meets a cold surface, it condenses and drips back down like rain.
- Hypothesis
- Write your own prediction, with a scientific justification.
- Variables
- Identify your independent, dependent and control variables, and explain how you will control them.
- Apparatus
- Large glass bowl, small cup, cling film, ice cubes in a small plastic bag, warm water, salt, stopwatch.
- Method
- Pour warm, slightly salty water into the bowl and place the empty cup in the middle.
- Cover the bowl with cling film and put the bag of ice on top, above the cup.
- Watch for droplets forming under the cling film and dripping into the cup, timing when the first drop falls.
- Taste-test is not allowed: instead, evaporate a few drops of the collected water to show no salt is left.
Safety. Use warm, not boiling, water, and take care with glass. Do not taste anything in the laboratory.
Then evaluate: which parts of the real water cycle does your model show, and which are missing?
Criterion-linked questions
Criterion B: inquiring and designing
Criterion C: processing and evaluating
Criterion D: reflecting on the impacts of science
Challenge questions
Harder problems in unfamiliar contexts. Plan before you calculate.
Topic check
Five questions picked at random from the whole topic. Take a new set whenever you like.
Review your mistakes
Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.
Your progress
Tracked separately for each skill, on this device only.
| Skill | Correct | Status |
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