What it shows
Heat flows from hot things to cooler surroundings. Materials like thermocol, cloth and air pockets slow this flow and are called insulators, while metal lets heat through quickly. A lid matters because much heat escapes with rising warm air and steam.
The science
Heat moves in three ways: conduction through the material of the cup, convection as warm air and steam rise from the surface, and radiation from the hot surface. A steel cup conducts heat to the outside quickly, so it feels hot to touch and the tea cools fast. Thermocol is full of tiny trapped air pockets and air is a poor conductor, so the heat stays in. Covering the cup stops the warm air and steam from carrying heat away, which is why a lid makes such a big difference.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Four cups of similar size: steel, glass, ceramic (kulhad or china) and a thermocol or paper cup
- Hot water from a kettle, handled by an adult
- A thermometer
- A measuring cup
- Cardboard squares as lids
- A clock and a notebook
Safety
For this project: An adult must pour the hot water. Use water from a kettle that has been allowed to cool a little, not boiling, and keep the cups away from the table edge.
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.
Pour the same amount of hot water, say 150 ml, into each cup at the same time and record the starting temperature.
Leave all the cups uncovered and measure the temperature of each every 5 minutes for 30 minutes.
Write the readings in a table with one column per cup.
Empty and dry the cups, refill with fresh hot water and repeat the test with a cardboard lid on every cup.
Draw a line graph of temperature against time for each cup, with the lid results as dotted lines.
Touch the outside of each cup soon after filling and note which feels hottest; that cup is losing heat fastest.
Wrap the glass cup in a cloth or newspaper and test once more to see how much the wrapping helps.
Rank the cups from best to worst insulator and explain the ranking in your report.
What you should see
The thermocol cup keeps the water hottest and the steel cup cools quickest. Every cup stays warmer with a lid, and wrapping the glass in newspaper makes it almost as good as thermocol.
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 steel cup cool fastest?
Steel is a good conductor and carries heat quickly from the water to the outside air.
2Why is thermocol a good insulator?
It is full of tiny pockets of trapped air, and air conducts heat very poorly.
3Why does a lid help so much?
It stops warm air and steam from rising off the surface and carrying heat away.
4Which way does heat always flow?
From the hotter object to the cooler one.
Take it further
Design and build the best insulated cup you can from waste materials and test it against a shop-bought flask.
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.
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