Year 9 Science · Unit 3 · Lesson 8
Challenge Worksheet
Learning Goals
1. Explain why radiation is the only way the Sun’s energy can reach Earth.
2. Two otherwise identical model car shells are parked side by side in the sun in Darwin. One has a matte black exterior and the other has a polished aluminium exterior. (a) Explain which interior heats up faster, using absorption of radiation. (b) Just after sunset, suppose both interiors are at the same temperature and all other heat losses are equal. Predict which cools faster, and explain using emission of infrared radiation.
Investigation: which wrapping keeps water hot?
A class filled five identical cans with water at 75 °C. They wrapped four cans in a single layer of a different material, left one can bare, and measured the water temperature after 15 minutes.
| Wrapping | Start (°C) | After 15 min (°C) | Drop (°C) |
|---|---|---|---|
| None | 75 | 59 | 16 |
| Aluminium foil | 75 | 62 | |
| Cotton cloth | 75 | 63 | |
| Bubble wrap | 75 | 67 | |
| Wool | 75 | 68 |
Source: sample class results.
3. Complete the Drop column of Table 1. By what percentage did the wool reduce the temperature drop, compared with the bare can?
Reduction %
4. Explain why wool and bubble wrap worked best. Then explain why the foil helped only a little, and which method of heat transfer it reduces.
5. A student concludes: “Wool is the best insulating material.” Identify one weakness in how the test was done that makes this conclusion unsafe, and suggest one improvement.
Someone claims
“A vacuum flask blocks all heat transfer, so a drink inside will stay at exactly the same temperature forever. The designers eliminated conduction, convection and radiation completely. The drink is in a perfect thermal bubble: nothing can get in or out.”
6. Evaluate the claim. Say which parts are supported by science and which are not. Explain how a vacuum flask reduces each method of heat transfer, and which one it is least able to block.