Science 7–10 · Year 8
Insulation: cooling curves for cups wrapped in different materials
Physical sciences — Change, content group Energy transfers (NSW Stage 4 focus area)
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.
The idea
Thermal energy escapes from a hot object faster when the temperature difference is larger, and an insulating layer slows the transfer so the cooling curve flattens.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- scalds from 80 degrees C water
Controls
- teacher pours
- beakers not moved once filled
- digital probes rather than glass thermometers
Note
Heat or electrical energy is involved. Complete the school's risk assessment for the activity before the lesson, using CSIS 1.7 (Risk assessment – a pre-requisite for risk control) from the department's Chemical Safety in Schools package (2021 Technical Update), which the NSW Department of Education Science safety and compliance page names for risk assessment advice.
What you need
- identical 250 mL beakers or tin cans, 4
- wrappings: bubble wrap, cotton wool, aluminium foil, none, one 2-layer wrap each
- digital thermometers or data-logger probes, 4
- lids with a probe hole, 4
- kettle and 250 mL measuring cylinder, 1 each
- stopwatch, 1
How to do it
- Wrap three beakers in two layers of each material and leave the fourth bare. Fit the lids.
- Pour 200 mL of water at 80 degrees C into each beaker in quick succession, insert the probes and start the stopwatch.
- Record all four temperatures every minute for 30 minutes (a data logger can sample every 10 seconds).
- Plot temperature against time for all four on one graph.
- Calculate the cooling rate in degrees C per minute over the first 5 minutes and over the last 5 minutes for each beaker.
- Rank the wrappings and explain why the rate falls as the water cools.
- Identify two sources of error in the method, for example the water cooling while the four beakers are filled one after another, and explain how each could change the ranking.
What you should see
All four curves fall fastest at first and flatten as the water nears room temperature. The bare beaker cools fastest, and the wrapped beakers stay warmer than the bare one at every time. The first-5-minute rate is larger than the last-5-minute rate for every beaker, and more so for the faster-cooling ones: in Newton's law of cooling the ratio is e^(25k), 1.28 for k = 0.01 per minute and 1.65 for k = 0.02 per minute. The learner knows it worked when the wrapped beakers sit above the bare one at every time.
What changes
- What you change
- wrapping material
- What you measure
- water temperature over time (degrees C)
- What you keep the same
- water volume and starting temperature
- beaker type and lid
- room temperature and draughts
- thickness of wrapping
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Insulation adds heat to the water.
- Foil keeps things warm because it is shiny, whatever the surroundings.
- Cooling happens at a constant rate.
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)SC4-CHG-01SC4-WS-04SC4-WS-05SC4-WS-06
- Australian Curriculum v9AC9S8U05AC9S8I02AC9S8I04AC9S8I06
Sources
The pages the author read to write this activity.