What it shows
Dark paved surfaces absorb more sunlight and warm up more than grass or shade. Mapping temperatures across a school or street shows how towns become hotter than the countryside.
The science
Dark asphalt and concrete absorb most sunlight and store heat, while grass cools by evaporating water from leaves and soil and a tree casts shade. Buildings also trap heat and tall walls reduce wind. Air near the ground over a road can be several degrees warmer than over a lawn. The difference in temperature between a city and nearby countryside is called the urban heat island effect. Pale or reflective surfaces warm less because they reflect more light.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A thermometer reading to 100 degrees C, or two if possible
- An infrared thermometer if the school has one
- A small square of white card to shade the bulb
- A watch and a notebook
- A clipboard and a site sketch
- A tape measure
- A cap and water bottle
Safety
For this project: An adult must supervise, especially in hot weather. Do not touch very hot surfaces with bare hands. Wear a hat and drink water, and stay on footpaths away from traffic.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Choose six sites: an asphalt road, a concrete floor, a tin or tiled roof, bare soil, a grass lawn and the shade of a big tree. Draw a sketch map with them marked.
At each site, hold the thermometer 10 cm above the surface, shaded from direct Sun by the white card, and read the air temperature after two minutes.
If you have an infrared thermometer, aim it at the surface from 20 cm and note the surface temperature as well.
Take readings at 9 am, 12 noon and 3 pm on a clear day, always in the same order and the same way.
Write the readings in a table and draw a line graph with time on the horizontal axis and temperature on the vertical axis, one line for each site.
Find the difference between the hottest and coolest site at noon.
Test a white-painted and a black-painted tin lid in the Sun for 20 minutes to see the effect of colour directly.
Suggest three ways to cool the school, such as trees, white roofs and green strips, and say which readings support your ideas.
What you should see
A graph showing that the road and tin roof are warmest, the lawn and the tree shade cooler by several degrees, and that the black lid warms more than the white lid.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the urban heat island?
The effect by which built-up areas are warmer than nearby rural areas.
2Why is grass cooler than tar?
Grass reflects more light and cools by evaporation, while tar absorbs light and stores heat.
3Why shade the thermometer?
Direct sunlight would heat the thermometer itself and give a false reading.
4How do trees reduce heat?
They shade surfaces and release water vapour, which cools the air.
Take it further
Repeat the transect in summer and winter and compare, or measure a roof before and after it is painted white.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
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Investigatory Projects for Class 11 and 12
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