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Primary Science · Year 4Chapter 7 · Changing state and the water cycle
Year 4 Science · Changing state and the water cycle · Lesson 7.3

Year 4 Science: Evaporation

Part of the Year 4 Science changing state and the water cycle chapter. Chapter overview · whole chapter on one page

7.3

Evaporation

Year 4
M3: identify the part played by evaporation in the water cycle, and associate the rate of evaporation with temperature
Story. Aisha wets three cloths and hangs one on the sunny windowsill, one in the shady corner and one in the cool hallway. “Which one will dry first?” she asks. “Let us time them,” says Mr Patel.

Evaporation is when a liquid changes into a gas. Water at the surface of a puddle, a lake, the sea or a wet cloth turns into water vapour, which is a gas, and goes into the air. Evaporation happens at any temperature, but it happens faster when it is warmer.

The table shows the results of the drying test. The fastest result has the smallest number of minutes.

PlaceTemperature (degrees Celsius)Minutes to dry
Sunny windowsill2830
Shady corner1860
Cool hallway1290
0306090minutes to dry30 minSunny windowsill28 degrees60 minShady corner18 degrees90 minCool hallway12 degrees
The minutes to dry in each place: 30 minutes in the sunny windowsill, 60 in the shady corner, and 90 in the cool hallway.

Key ideas

  • Evaporation is when a liquid changes into a gas.
  • Evaporation happens faster when it is warmer.
  • Evaporation is part of the water cycle.
  • A wet cloth dries faster in a warm place than in a cool place.
Worked example 7.3.1
Which place dried the cloth fastest? Write the name of the place.

Method. Find the smallest number of minutes.

  1. Read the minutes. The minutes are 30, 60 and 90.
    30 is the smallest
  2. Name the place. The sunny windowsill took 30 minutes, the fastest.
    Sunny windowsill
  3. Write the answer.
    Sunny windowsill

Check. The sunny windowsill was the warmest place. ✓

Worked example 7.3.2
How many minutes faster was the sunny windowsill than the shady corner? Write the number.

Method. Subtract the two times.

  1. Read the two times. The shady corner took 60 minutes, and the sunny windowsill took 30.
    60 and 30
  2. Subtract. 60 minus 30 is 30.
    60 - 30 = 30
  3. Write the answer.
    30

Check. Check: 30 plus 30 makes 60. ✓

Worked example 7.3.3
Is evaporation faster when the place is warmer? Write yes or no.

Method. Look at the temperatures and the times together.

  1. Compare them. The warmest place, 28 degrees, dried fastest, in 30 minutes.
    warmest, fastest
  2. Decide. So evaporation is faster when it is warmer, and the answer is yes.
    yes
  3. Write the answer.
    yes

Check. The pattern is the same for all three places. ✓

Watch out

Watch out: evaporation is not the same as boiling. Evaporation happens at the surface of the liquid at any temperature, while boiling needs a high temperature.

Try it at home or school (with a grown-up). Wet two tea towels with a grown-up. Hang one on a sunny windowsill and one in a shady place, and check each one every 30 minutes. Write down which dries first. Do not use hot water.

Exam tip

Grown-up tip. Ask: “Which towel dried first? Was it the warm place or the cool place?” Let your child time the towels and write the results in a table.

Exercise 7C  Evaporation

1
FWhat is the word for when a liquid changes into a gas at its surface? Write the word.
2
FWhich place dried the cloth fastest? Write the name of the place.
3
FWhich place dried the cloth slowest? Write the name of the place.
4
FHow many minutes did the cloth take to dry in the shady corner? Write the number.
5
FThe sunny windowsill was 28 degrees Celsius. What was the temperature of the cool hallway? Write the number.
6
FIs evaporation faster when it is warmer? Write yes or no.
7
FDoes evaporation happen in the cool hallway? Write yes or no.
8
PSHow many minutes faster was the sunny windowsill than the cool hallway? Write the number.
9
PSWhich dries faster: a warm towel or a cold towel? Write the word: warm or cold.
10
PSRuby says the cloth dried faster in the cool hallway because it was cooler. Is Ruby right? Write yes or no.
11
PSWorking scientifically. Predict which will dry faster: a puddle in the sun, or a puddle in a shady place. Write one prediction with a reason.
12
RExplain why washing hung outside on a warm, windy day dries quickly. Write one sentence.

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