Properties of materials
The idea
Everything around you is made of some material — wood, metal, plastic, glass, paper, cloth. Each material has properties, which are things you can notice or test about it: hard or soft, bendy or stiff, rough or smooth, see-through or not, soaks up water or keeps it out. Properties matter because they decide what a material is good for. A window needs a see-through material, so glass works. A towel needs a material that soaks up water, so cloth works.
To find a property, you test the material with your senses or a simple try-out. Press it: does it dent? Bend it: does it snap or spring back? Drip water on it: does the water soak in or sit on top? One mix-up to avoid: the object and the material are not the same thing. A paper boat and a paper hat are different objects, but they are the same material, so they share the same properties — both go soggy in water. Changing the shape does not change what the material is like.
Worked example
You want to make a rain hat, and you can use paper, cotton cloth, or a plastic sheet. You drip 10 drops of water onto a flat piece of each material and wait one minute. Which material is best for the rain hat?
- First decide which property matters for the job. A rain hat must keep water off your head, so you are testing whether water soaks in or stays on top.
- Test the paper: the 10 drops sink in fast, and after a minute the paper is wet through and starting to fall apart. Paper soaks up water.
- Test the cotton cloth: the drops slowly spread into the cloth, and after a minute the cloth is damp on both sides. Cloth soaks up water too, just more slowly.
- Test the plastic sheet: all 10 drops sit on top in little beads, and the underside is still dry after a minute. Plastic does not let water through.
- Compare the results to the job. Only the plastic kept its other side dry, so it is the only material here with the right property for a rain hat.
Answer. The plastic sheet is the best choice, because it was the only material that did not soak up the water.
Check your understanding
- Which properties would matter most if you were choosing a material for a swing seat, and how could you test for them?
- Why does cutting a material into a new shape leave its properties the same?
- What should you keep the same when testing two materials, so the comparison is fair?
- How would you explain to a friend the difference between an object and the material it is made from?