Choosing the Right Material for the Job

Builders and engineers choose a material by matching its properties to the job it must do.

• A cooking pot must sit on a hot stove without melting, so we use metal — strong and able to handle heat.
• A window must let light in and be hard, so we use glass — transparent and hard.
• A shopping bag must be light and keep the rain out, so we use plastic — light and waterproof.

We can also make a material better for a job. Builders make a wall stronger by using bricks and cement together — this is called combining materials. We can waterproof a cardboard box by wrapping it in plastic, so the rain cannot soak in.

Worked example. A farmer needs a fence to keep goats in. Should it be made of paper, glass or metal wire?

Metal wire — it is strong, it does not break when a goat pushes against it, and it lasts outside in the rain and sun. Paper would tear at once, and glass would shatter. The job needs 'strong and long-lasting outdoors', and metal has those properties.