Science 7–10 · Year 10

Thermal expansion of water: a flask thermometer for sea-level rise

Science understanding: Earth and space sciences (NSW Stage 5 focus area: Environmental sustainability)

Practical, model not builtLow risk

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The idea

Water expands as it warms, so an ocean that absorbs heat takes up more room and sea level rises even before any ice melts.

Safety card

Low riskAn adult supervises

Hazards

a glass tube pushed into a bung can snap and cut the hand
hot lamp: an infrared heat globe runs hotter than a lighting globe

Controls

the teacher fits the tube, lubricated with glycerol and with the hand protected by a cloth, or uses a plastic tube
do not touch the lamp, keep it clear of paper, and let it cool

Note

No hazardous chemical and no flame: a generic classroom risk assessment (CSIS 1.7 or RiskAssess) covers trips, spills, radiant lamps and sharp edges.

What you need

1 conical flask, 250 mL, filled completely with water at about 20 degrees C and coloured with 2 drops of food colouring
1 two-hole rubber bung carrying a clear tube of 3 mm internal diameter and 30 cm length, and a thermometer (bungs prepared by the teacher)
a clamp, stand and a ruler fixed beside the tube; a marker
a clamp lamp with a 150 W R125 infrared heat globe in place of the UCAR activity's 100 W bulb, which is no longer sold in Australia, or a water bath at 30 degrees C

How to do it

Push the bung in until water rises a few centimetres up the tube with no air bubbles in the flask; mark the level and record the temperature.
Warm the flask with the lamp for 5 to 10 minutes, or stand it in the 30 degrees C bath, recording temperature and water level every minute.
Stop when the thermometer reads about 30 degrees C and calculate the volume change as the rise times the tube's cross-sectional area.
Compare the measured change with the prediction from the NIST densities of water.
Repeat three times from the same starting temperature and find the mean rise.
Relate the result to the ocean: the IPCC gives a global mean sea-level rise of 0.20 m from 1901 to 2018, with thermal expansion one of the causes.

What you should see

From NIST densities (998.21 kg/m^3 at 20 degrees C, 995.65 kg/m^3 at 30 degrees C), 250 mL of water expands by 0.643 mL between 20 and 30 degrees C; in a 3 mm tube (cross-section 7.07 mm^2) that is a rise of 91 mm, and in a 2 mm tube 205 mm. The same flask gains only 0.373 mL between 10 and 20 degrees C, because cold water expands less per degree, and water below about 4 degrees C contracts as it warms. The glass flask also expands slightly, so the measured rise comes out a little under the prediction. The learner knows it worked when the mean rise is within about 10 percent of 91 mm for a 20 to 30 degrees C run.

What changes

What you change: water temperature
What you measure: height of water in the tube (volume change)
What you keep the same: volume of water
tube diameter
starting temperature
no air in the flask

Common misconceptions

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

Sea level rises only because ice melts; warming water expands as well.
All water expands when it is heated; between 0 and about 4 degrees C it contracts.
A tiny expansion cannot matter; spread through the depth of an ocean, a small fractional change becomes a measurable rise.

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 7-10 Syllabus (2023), NSW Education Standards Authority (implemented from 2026; codes read at curriculum.nsw.edu.au on 22 and 23 September 2026)SC5-ENV-01 SC5-WS-01 SC5-WS-04
Australian Curriculum v9AC9S10U04AC9S10I03AC9S10I04

Sources

The pages the author read to write this activity.

All Concept Studio activities