Properties of materials

Hey, Michael! Look around, pick something. How would you describe it? This table is hard. Brown.

My shirt is white and light. This glass is hard, but it breaks easily! All these objects are made of different materials — wood, cotton, glass. All materials have distinct characteristics — they can be hard, soft, heavy, light, stiff, easy to break, have a particular colour… These are some of the properties of materials. Let’s take another look at the objects Michael picked, and see how they interact with light.

Some materials, such as glass, let light through. They are see-through, or transparent. Other materials, such as wood, don’t let the light through — they are opaque. Opaque materials have a colour: wood is brown, cotton is white. - And this metal fork is silver-grey and shiny! Shiny is not a colour, but it is another property materials can have.

Many metals reflect light in a way that makes them shiny, or lustrous. Other materials, such as paper or cotton, don’t have this property - they are dull. Some properties of materials can't be seen like these. But we can still measure or test them. What’s that you’ve got there, Michael?

Oh, I just found this marble and a rubber ball in the drawer here... Perfect! We can use these to test some properties of materials. Try squeezing them. When you squeeze it, the rubber ball changes its shape.

When you release it, it goes right back to its original shape. But no matter how hard you squeeze the glass marble, that doesn’t change its shape at all. The rubber ball is elastic. The glass marble resists bending - it is stiff. What happens if you drop them on the floor, Michael?

The rubber ball bounces back, unaffected by hitting the floor. And... stop! Don't drop the glass marble! It might crack!

Rubber is a material that absorbs impact very well, but glass has a tendency to break easily — it is brittle. Do you see that fridge magnet? It sticks on the fridge door, but if you try that against a concrete wall or wooden table, the magnet just doesn’t stick. Certain materials, such as the metal the fridge door is made of, are attracted by magnets — they are magnetic — while others are not. Let’s move over to the stove.

You might have noticed that metal handles on a pot can get much hotter than, say, plastic ones. This is because heat travels differently through different materials. Different materials have different levels of thermal conductivity. Materials through which heat travels very well, like many metals, are thermal conductors. Materials that conduct heat poorly are thermal insulators.

Materials also differ in the way they conduct electricity. Electric cables, like on an electric kettle, are made of copper. Copper conducts electricity from the socket to the kettle. But you don't want the cable to conduct electricity to you, if you touch it! So the copper is covered in plastic, an insulator.

Properties of materials play important roles in everyday lives. We use different materials to make furniture, clothes, all kinds of different objects. Sometimes, we mix materials with different properties to make them work the way we need. Take a look at the objects around you. What materials are they made of?

What properties do those materials have? Why do you think the objects are made of those materials, and not anything else?