Year 7 Science · Unit 2 · Lesson 3
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims...
"Engineers should always choose the densest material available for construction projects. The densest material is always the strongest, so a denser bridge or building will always be safer and last longer. Gold (density 19.3 g/cm³) would make the perfect building material — it's the densest common metal, so it must be the strongest. Diamond (density 3.5 g/cm³) is less dense than gold, so it can't be as useful for engineering."
(a) What part of this claim is supported by the science you have learned? (Is any part of it correct?)
(b) What is misleading or incorrect in this claim? Give at least TWO specific examples from the lesson (or from real life) that show density alone does not determine how useful a material is.
(c) What other physical properties (besides density) would an engineer need to consider when choosing a material for a bridge? List at least THREE properties and explain why each one matters.
1. Ice floats on water, but most solids sink in their own liquid when melted. This unusual property of water has a critical effect on Australian alpine ecosystems (such as the Snowy Mountains). Using your knowledge of density, explain: (i) why ice floats on water, and (ii) what would happen to organisms living in alpine lakes if ice were denser than water.
2. A science journalist writes: "Graphite — the material in your pencil — is the exception that proves the rule: it's a non-metal that conducts electricity." Design a simple experiment a Year 7 student could carry out to test whether a pencil lead (graphite) actually conducts electricity. Identify the independent variable, the dependent variable, and one controlled variable.
Wrap Up
In one sentence, what was the main idea of this lesson?