What it shows
A dark surface soaks up most of the sunlight that falls on it and gets hot, while a white or shiny surface reflects most of it and stays cooler. This is why we wear light colours in summer and why solar heaters are painted black.
The science
Sunlight carries energy. When it falls on a surface, some is absorbed and warms the surface and some is reflected away. Black surfaces absorb almost all the light that hits them, which is why they look dark, so they heat up quickly. White and shiny surfaces reflect most of the light, so they gain little heat. The water inside each tin is warmed by the metal, so measuring the water temperature shows how much energy each colour collected.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three identical empty tins or small bottles (free)
- Black paint, white paint and aluminium foil
- Water and a measuring cup
- A thermometer (a digital one from a chemist works well)
- A sunny spot and a clock
Safety
For this project: An adult should check the tin edges are not sharp, and the water can get hot enough to be uncomfortable, so handle it with care.
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.
Paint one tin black and one white and wrap the third in foil shiny side out; let the paint dry.
Pour exactly the same amount of water, say 200 ml, into each tin and measure the starting temperature of each.
Stand the three tins side by side in full sun at the same time, with nothing shading any of them.
Measure the water temperature in each tin every 15 minutes for two hours and write it in a table.
Stir gently before each reading so the water is evenly warm.
Draw a line graph with one line for each tin, time along the bottom and temperature up the side.
Bring the tins into the shade and keep measuring for another hour to see which one cools fastest.
Write what the graph shows and link it to light clothes in summer and black solar water heaters.
What you should see
The black tin warms fastest and reaches the highest temperature, often 10 degrees or more above the foil tin after two hours. The white and foil tins stay much cooler. In the shade the black tin also cools fastest.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the black tin get hottest?
A black surface absorbs almost all the sunlight that falls on it.
2Why does the foil tin stay cool?
A shiny surface reflects most of the sunlight away.
3Why do people wear white in summer?
White cloth reflects sunlight, so the body gains less heat.
4Why are solar water heaters painted black?
To absorb as much sunlight as possible and heat the water quickly.
Take it further
Add a tin painted red and one painted blue and find where they sit between black and 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
Science projects
Easy Science Projects for Class 1 to 5
Simple, safe projects young children can make with a little help