Lesson 23: Properties of Materials
Hardness, flexibility, elasticity, magnetism, and conductivity help describe and compare materials. Observations and simple tests show why a material may suit one job better than another.
Key Ideas
- Observations and tests help us identify materials. One clue, such as color, may not be enough.
- Materials have properties we can compare, such as hardness, flexibility, and how well they pass heat or electricity.
- Flexible materials bend without breaking. Elastic materials return to their original shape after bending or stretching.
- We choose a material because its properties suit the job we need it to do.
- Scientists and engineers can combine or develop materials when existing ones do not meet a need.
Vocabulary
- Hardness: How much a material resists being scratched or dented.
- Flexibility: The ability to bend without breaking; it may spring back or stay bent.
- Elasticity: The ability to return to the original shape after bending or stretching. (Example: rubber)
- Brittle: Breaks instead of bending. (Example: glass, dried clay, a cracker)
- Malleable: Can be hammered or rolled into a new shape without breaking.
- Conductivity: How well a material lets heat or electricity pass through it.
Discussion Questions
- Why isn't there one “best” material for everything? What might make a material perfect for one job but terrible for another?
- What is the difference between flexible, elastic, and brittle? Can you think of an everyday object that demonstrates each one?
- Why would an engineer want to test a material's hardness, weight, flexibility, or conductivity before using it?
- If you were given an unknown material, how could you use your senses and simple tests to figure out what it might be?
- Imagine you need to design a bridge. Which properties would you want your materials to have, and why?