Heat sources. Thermal expansion
Answers are for parents and teachers.
1
Write five heat sources.
The Sun, fire, electric current, friction, a hot spring.
2
Give one useful and one harmful example of thermal expansion.
Useful: thermometer, bimetallic thermostat; harmful: buckling of rails or bridges.
3
Why do fish survive in a lake in winter? Recall water at 4 °C.
Ice floats and insulates; the bottom stays at about 4 °C.
4
Discuss with an adult how a railway handles expansion of rails and write two sentences.
Sample: gaps are left between rails; on modern lines rails are welded and firmly fixed.
5
Put an empty plastic bottle with a balloon on its neck in a refrigerator (with an adult): what happens? Explain.
The air cools and contracts, so the balloon is drawn slightly inward.