Properties of Materials: Metals, Polymers, Ceramics and Composites — Answers
Answer sheet with model answers and success criteria for the 8th Grade states of matter & materials worksheet.
Success TutoringWorksheetsAnswer sheet8th Grade · Science · States of Matter & MaterialsProperties of Materials: Metals, Polymers, Ceramics and Composites — Answers
Part A: Describing properties
The properties of a material describe how it behaves. Engineers choose materials whose properties suit the job.
Important properties include strength, hardness, flexibility, brittleness, malleability, thermal and electrical conductivity, melting point, density and whether a material is waterproof or transparent.
- Hardness
- Flexibility
- Brittleness
- Thermal conductivity
- Malleability
- Tensile strength
- Resists being scratched or dented
- Bends without breaking
- How well heat passes through it
- Resists being pulled apart
- Can be hammered or pressed into shape
- Breaks or shatters suddenly when hit
Answer: Hardness → Resists being scratched or dented; Flexibility → Bends without breaking; Brittleness → Breaks or shatters suddenly when hit; Thermal conductivity → How well heat passes through it; Malleability → Can be hammered or pressed into shape; Tensile strength → Resists being pulled apart
Answer: False
Glass is hard (difficult to scratch) but brittle, so it shatters easily when hit or bent. Hardness and strength are different properties.
Answer: A raincoat must keep rain out to keep the wearer dry. An oven tile is not exposed to rain; it needs to withstand high temperatures instead.
Part B: Groups of materials
Classify each material, then answer the questions.
Metals (iron, copper, aluminum): strong, shiny, malleable, good conductors of heat and electricity. Polymers (plastics, rubber, wool): light, flexible, usually insulators, can be molded. Ceramics (clay, glass, porcelain): hard, heat resistant, insulators, but brittle. Composites combine two or more materials to get the best properties of each, such as reinforced concrete.
- AMetal
- BPolymer
- CCeramic
- DComposite
Answer: Metal
Copper is a metal: shiny, malleable and an excellent conductor.
- AMetal
- BPolymer
- CCeramic
- DComposite
Answer: Polymer
Plastics are polymers made of long chain molecules.
- AMetal
- BPolymer
- CCeramic
- DComposite
Answer: Ceramic
Porcelain is a ceramic made by heating clay to a high temperature.
- AMetal
- BPolymer
- CCeramic
- DComposite
Answer: Composite
Combining concrete (strong when squashed) with steel (strong when pulled) makes a composite.
- ABrittle
- BGood electrical conductor
- CLow density
- DTransparent
Answer: Good electrical conductor
Metals conduct electricity and heat well because they contain free-moving electrons.
Answer: Any two of: very high melting point, heat resistant, poor conductor of heat (thermal insulator), hard, does not react or corrode.
Answer: Copper is an excellent electrical conductor, so it carries the current. The polymer is an electrical insulator, so it stops the current reaching anyone who touches the cable. It is also flexible and waterproof.
Answer: False
Ceramics are hard but brittle, so they crack or shatter when dropped.
Part C: Testing strength
Students tested three strings of equal length and thickness by hanging masses from them until they broke. They did three trials for each.
String A: 2.0 kg, 1.1 kg, 2.1 kg · String B: 3.2 kg, 3.4 kg, 3.0 kg · String C: 5.1 kg, 4.9 kg, 5.0 kg (mean 5.0 kg)
Answer: 3.2 kg
- Mean = (3.2 + 3.4 + 3.0) ÷ 3
- = 9.6 ÷ 3 = 3.2 kg
Answer: String C, because it held the greatest mean mass before breaking (5.0 kg).
Answer: Treat it as an outlier: check it or repeat that trial, and leave it out of the mean, because it is very different from the other results and probably due to an error (for example, a damaged string).
Part D: Choose a material
Model answer: Steel is very strong and cheap, but it is dense, so a steel frame is heavy. Aluminum is less dense than steel, so the frame is lighter, and it is strong enough and does not rust easily, although it costs more than steel. Carbon fiber composite is very strong and has a very low density, giving the lightest frame, but it is the most expensive and can crack if hit hard. For a racing bicycle, low mass matters most because it lets the rider go faster with less effort, so carbon fiber composite is the best choice if cost is not the main concern; aluminum is a good, cheaper alternative.
Success criteria:
- Compares strength of the materials
- Compares density or mass of the frames
- Compares cost
- Makes a recommendation linked to the needs of a racing bicycle
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
Great work. Here's what to try next: