Year 8 Science · Unit 2 · Lesson 04
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Learning Goals
Match each model to what it does
Write the matching letter in the middle column. Each letter is used once.
| Model | Letter | What it shows, and what it leaves out |
|---|---|---|
| Globe | A. Predicts storms and bushfire weather from large-scale patterns, without tracking every air molecule. | |
| Road map | B. Shows the patterns inside the body a doctor needs for diagnosis, without showing every cell. | |
| Computer weather model | C. Shows the roads you need to find your way, leaving out trees, houses and potholes. | |
| MRI scan | D. Shows the double-helix shape of a molecule, but not its chemical details. | |
| Plastic DNA model | E. Shows the true shapes of the continents and Earth’s curve, but mountains are far too small to feel. |
1. Every model in the table leaves something out. State what a scientific model is, and why leaving out detail can make it more useful.
2. A Year 8 student builds a Bohr model from balls and wire rings and says it shows “exactly what an atom looks like”. Give one thing her model shows well, and explain one way it misleads.
Read the data
Scenario: planning a trip with a map
A student measured the straight-line distance from her town to three other towns on a road map, where 1 cm on the map stands for 2 km on the ground. After each trip, she recorded the distance the car actually drove.
| Trip | Straight line on the map (cm) | Straight-line distance (km) | Distance driven (km) |
|---|---|---|---|
| To Town B (flat farmland) | 4.0 | 8 | 9 |
| To Town C (along the coast) | 7.5 | 19 | |
| To Town D (over a mountain range) | 3.0 | 14 |
Source: sample trip log (distances rounded to the nearest km).
3. Use the map scale to complete the straight-line distances for Towns C and D. Show your working.
Town C km
Town D km
4. Every trip was longer than the straight-line distance, and the trip to Town D was more than twice as long. Explain what the map model leaves out that causes this, and whether the map is still a useful model for planning trips.
5. A student says: “If atomic models are not exact pictures, we should not use them.” Evaluate this conclusion using Claim, Evidence and Reasoning. Use the Bohr model and the road map from this sheet as your evidence.
Match each model to what it does
Globe → E; Road map → C; Computer weather model → A; MRI scan → B; Plastic DNA model → D.
1. A simplified representation used to explain, describe or predict something that is hard to observe directly. Leaving out detail lets it focus on the pattern that matters for the job, so it is clearer and easier to use. [2 marks: 1 definition, 1 reason]
Your Turn
2. Shows well (any one): a central nucleus with electrons outside it; electrons in separate levels. Misleads (any one, explained): electrons do not travel in fixed circular paths, they are found in a cloud of likely positions; atoms are not made of balls and wire, and the real atom is mostly empty space. So the model is useful but not an exact picture. [3 marks: 1 strength, 1 limitation, 1 explanation]
Read the data
3. Town C: 7.5 × 2 = 15 km. Town D: 3.0 × 2 = 6 km. [2 marks: 1 each]
4. The straight line leaves out the real shape of the roads: roads bend around coastlines and wind up and over mountains, so the car drives further. The map also flattens hills, so the steep, winding mountain road to Town D (14 km for a 6 km straight line) is most affected. The map is still useful: it shows which roads connect the towns and gives a quick first estimate; it just should not be used alone to predict exact driving distance. [4 marks: 1 roads are not straight, 1 terrain/mountains left out, 1 links to Town D data, 1 judgement of usefulness]
Show What You Know
5. Marking guide: 1 claim: the conclusion is weak; 2 reasoning: models are simplified on purpose to explain, predict and communicate things that are hard to observe directly, so being useful does not require being exact; 2 evidence: the Bohr model is wrong about neat circular paths but correctly shows a central nucleus with electrons in separate levels; the road map leaves out bends and hills but still shows which roads connect the towns; 1 stronger statement, e.g. “We should use models for what they explain well, know their limits, and improve them when new evidence appears.” [6 marks]
Common error to watch for: in Q4, saying the map is “wrong” and so useless. Push students to name exactly what the model leaves out and what job it still does well.