What it shows
Spoons of steel, aluminium, wood and plastic with butter dabbed on the handles are placed in hot water, and the butter melts and drops first on the best conductor. It shows that metals conduct heat well and wood and plastic poorly.
The science
Heat travels in solids by conduction, as the vibrating particles pass energy to their neighbours. In metals free electrons also carry energy quickly, so metals are good conductors, while wood and plastic have no free electrons and conduct poorly, making them insulators. Aluminium conducts about 200 W/m K and steel about 15 to 50, against about 0.2 for wood and plastic. The butter melts at about 32 °C and acts as a visible detector.
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.
- Spoons or rods of the same size made of steel, aluminium, wood and plastic
- Butter or ghee, a small dab for each
- A deep steel pot or a big jug of hot water, about 70 °C
- A stopwatch
- A thermometer
- Tongs or a cloth
- A clamp, or clips and a stand to keep spoons upright
Safety
For this project: An adult must heat and pour the hot water and keep it away from children. Use hot tea-temperature water, not boiling. Hold the spoons by a cloth or clip, not bare hands, and do not touch the hot water.
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.
Stick a dab of butter, the same size for each, at the end of each handle, 15 cm from the bowl end.
Fix the spoons upright or at a slant with clips so that the spoon bowls sit in the pot and the handles point out above.
An adult pours hot water into the pot to the same level on every spoon.
Start the stopwatch at once and watch the butter, noting when each dab starts to melt and when it slides or falls.
Write the order and times for each spoon in a table. Stop after 10 minutes.
Measure the temperature of the water at the start and the end to be sure it did not change much.
Repeat the whole test once more with fresh dabs and average the two readings.
Make a list of everyday insulators and conductors, such as pan handles and the pan base, and explain why they are made of those materials.
What you should see
The butter on aluminium melts first, followed by steel, while the butter on wood and plastic barely melts in 10 minutes.
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 conduction?
The transfer of heat through a solid from hotter to cooler particles without the material itself moving.
2Why do metals conduct better?
They have free electrons that carry energy quickly.
3Why is the pan handle made of plastic or wood?
These are insulators, so the handle stays cool.
4Why must the dabs be equal?
To make a fair test; bigger dabs would take longer to melt.
Take it further
Repeat with a copper wire and a glass rod and place them in the order of conductivity.
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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