Evaporation race: sun, shade, wind and surface area

The idea

Evaporation is faster when water is warmer, when the air is drier or moving, and when more surface is exposed, and the rate can be measured as mass lost per hour.

What you need

• 4 identical shallow dishes (about 15 cm across) and 1 tall narrow jar
• 100 mL water in each, measured by cylinder
• kitchen balance reading to 1 g
• a thermometer and, if available, a hygrometer
• positions: sunny windowsill, shaded bench, in front of a small fan on low, and a covered dish as the control

How to do it

1. At the start of the school day, weigh each container with its 100 mL of water and record the mass. In a 15 cm dish, 100 mL is only about 5.7 mm deep, which an open dish can lose in one to two days, so the test runs over one school day.
2. Place one dish in the sun, one in shade, one in front of the fan, one covered with cling film, and the tall jar beside the shaded dish.
3. Weigh every container every 2 hours until the end of the school day and record the mass.
4. Record the air temperature at each position at each weighing.
5. Work out grams lost per hour for each container over the day and graph them as columns.
6. Explain each difference using warmth, moving air and surface area; check that the covered dish lost almost nothing.

What you should see

The fan dish and the sun dish lose the most mass per hour, the shaded dish less, the tall jar (small surface) least of the open containers, and the covered control loses almost nothing, which checks that the weighing itself is steady. One gram lost is one millilitre evaporated, so the graph is an evaporation rate in millilitres per hour; for a 15 cm dish (176.7 square centimetres), 1 g per hour is 1.36 mm per day. At the model's still-air rate of 3.2 mm per day the shaded dish loses about 2.4 g per hour, so a 6-hour school day gives a clear reading on a 1 g balance, while a 5-day run would empty the open dishes. The rate constant in the model is fitted from the class's own data, so the model reproduces the class result by construction; what it predicts is how the rate changes with temperature and humidity.

What changes

What you change

position (sun, shade, fan) or container shape

What you measure

mass lost per hour

What you keep the same

• starting volume
• weighing times
• same room where possible

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Water only evaporates when it boils.
• The water soaked into the dish.
• Wind makes water colder so it evaporates less (moving air carries vapour away, so it evaporates more).

Safety card

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Science and Technology K-6 Syllabus (2017), current, taught until 2026; the 2017 syllabus has no water-cycle content; evaporation and condensation fall under this Stage 2 changes-of-state outcome ('recognise that a change of state can be caused by adding or removing heat'); code read from the syllabus document on 22 September 2026ST2-6MW-S
• Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST2-1WS-S
• Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST2-PQU-01ST2-DAT-01
• Australian Curriculum v9AC9S4U02AC9S4I02AC9S4I03AC9S4I04AC9S4I05

Sources

The pages the author read to write this activity.

1. www.scootle.edu.au/ec/search?accContentId=AC9S4U02
2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
3. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
4. primaryconnections.org.au/v84-sequences/water-works
5. primaryconnections.org.au/v84-sequences/change-detectives