Science and Technology K–6 · Year 3

Black can, white can: which warms faster in the sun?

Science understanding: Physical sciences

Practical, model not builtLow risk

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The idea

The Sun is a source of heat energy, and a dark surface absorbs more of it than a light one, so water in a black can warms faster than water in a white can.

What you need

2 identical clean 375 mL aluminium cans, one painted matt black and one matt white (paint dry)
2 thermometers (0 to 50 degrees Celsius) or 2 probe thermometers
200 mL tap water per can, measured with a cylinder
cardboard collars to hold the thermometers
a sunny, windless spot and a timer

How to do it

Fill each can with 200 mL of the same tap water and record the starting temperature of both.
Stand both cans side by side in full sun with the thermometers in the water, out of the shadow of anything.
Read both thermometers every 2 minutes for 20 minutes and record the readings.
Move both cans into the shade and keep reading for 10 more minutes.
Graph temperature against time for both cans on one set of axes.
Repeat on another day, or swap the thermometers between cans, to check the difference is real.

What you should see

The black can warms faster and reaches a higher temperature; in the shade both begin to cool. Upper bound from energy: a 375 mL can is about 6.6 cm across and 11.5 cm tall, so the area it presents to the beam is about 0.008 square metres (the wall's projected area, 0.066 x 0.115 = 0.0076 square metres, plus part of the 0.0034 square metre lid, depending on how high the Sun stands), not the whole curved wall. With about 800 W per square metre of sunlight on that area, a black surface absorbing 95 percent receives 6.1 W, which over 20 minutes is 7.3 kJ, enough to raise 200 g of water by 8.7 degrees Celsius with no losses; a white surface absorbing about 20 percent could gain 1.8 degrees. Real gains are lower because the whole outside of the can, about 0.027 square metres, loses heat to the air, but the black can's gain is several times the white can's.

What changes

What you change: colour of the can
What you measure: water temperature every 2 minutes
What you keep the same: water volume
starting temperature
can size
position in the sun
time in the sun

Common misconceptions

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

Black things make heat (they absorb more of the Sun's energy; they do not create it).
Shade is a source of cold.
The Sun heats the air and the air heats the can (sunlight warms the can directly: the black can gains faster than the white can although both sit in the same air, which the air alone cannot explain).

Safety card

Low riskLearners carry it out

Hazards

sun exposure
sharp can rims

Controls

hats and sunscreen for learners
file or tape the rims
cans placed by an adult

Note

Risk assessment before the lesson using Primary RiskAssess or the school's own template.

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-ST ST2-1WS-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-01
Australian Curriculum v9AC9S3U03AC9S3I02AC9S3I03

Sources

The pages the author read to write this activity.

All Concept Studio activities