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Science and Technology K–6 · Year 3

Cooling curve: how fast a cup of warm water loses heat

Science understanding: Physical sciences

Practical, model not builtLow risk

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The idea

A warm object loses heat to cooler surroundings, quickly at first and more slowly as the temperatures get closer, and a lid or insulation slows the loss.

Safety card

Low riskAn adult supervises

Hazards

  • water at 60 degrees Celsius

Controls

  • teacher pours
  • cups on a tray away from the bench edge
  • no carrying of hot cups by learners

Note

Hot water above 50 degrees Celsius is poured by the teacher. Risk assessment before the lesson using the NSW Department of Education Chemical Safety in Schools package (CSIS 1.7 Risk Assessment) or Primary RiskAssess.

What you need

  • 2 cups of the same size: one foam cup with a lid, one open plastic cup
  • 2 thermometers (0 to 100 degrees Celsius) or 2 probe thermometers
  • 200 mL warm water at about 60 degrees Celsius per cup (teacher pours)
  • room thermometer
  • timer
  • graph paper

How to do it

  1. Record the room temperature.
  2. Teacher pours 200 mL of 60 degree water into each cup; put the lid on the foam cup with the thermometer through it.
  3. Read both thermometers every 2 minutes for 20 minutes and record the readings in a table.
  4. Plot temperature against time for both cups on one graph.
  5. Describe the shape of each line: steep at first, then flatter.
  6. Work out the temperature drop in the first 4 minutes and in the last 4 minutes for each cup.

What you should see

Both lines fall and flatten toward room temperature; the open cup falls faster. With a cooling constant k of 0.03 per minute, room at 22 degrees Celsius and a start of 60, the model gives 42.9 degrees Celsius after 20 minutes; a lidded foam cup has a smaller k (measured from the learner's own data as the slope of ln(T minus room) against time) and stays warmer. The drop in the first 4 minutes is always larger than in the last 4 minutes.

What changes

What you change
cup type (open plastic or lidded foam)
What you measure
temperature every 2 minutes
What you keep the same
  • water volume
  • starting temperature
  • room temperature
  • position on the bench

Common misconceptions

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

  • Water cools at a steady rate, the same number of degrees every minute.
  • A lid keeps the cold out (it slows heat leaving).
  • The water eventually gets colder than the room.

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; code read from the syllabus document on 22 September 2026ST2-8PW-STST2-1WS-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-DAT-01
  • Australian Curriculum v9AC9S3U03AC9S3H01AC9S3I03AC9S3I04

Sources

The pages the author read to write this activity.

  1. www.scootle.edu.au/ec/search?accContentId=AC9S3U03
  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/teaching-sequences/year-3/scorching-swings-and-slides
  5. edu.rsc.org/resources/insulation-investigation/4011187.article

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