Hard and soft materials



You can compare the hardness of different materials by seeing how many different surfaces they scratch. The test surfaces should be from scrap materials and not be on objects that people still use!
If, for example, you choose a hard material like a steel nail, you will find it will scratch many materials. A copper coin will scratch fewer materials and so must be softer. A fingernail will scratch the least number of materials and must therefore be softer still.

Where are the hardest surfaces found in the home?
Most probably in the kitchen. The work tops are hard to cope with the preparation of food. The sink and draining board are hard to cope with the washing up. The plates are hard to cope with food being cut up on them, and knives and forks are hard because they have to cut and hold the food when you eat. The floor may be covered in hard kitchen (quarry) tiles. Think about how many meals are prepared a day in your kitchen, then think about how many meals are prepared in a week, month and year and you will realise why the surfaces need to be hard - if they were soft they would soon wear away.
Where are the hardest surfaces outside?
The hardest surfaces are those which have to stand up to a great deal of hard wear. Pavements have a hard surface to stand up to the pounding of shoes and boots as people walk and run along. Roads have hard surfaces to stand up to the tyres of cars and lorries rolling over them. Buildings need to be made with hard, strong materials and tall blocks are often made with reinforced concrete.

Are diamonds used for anything because they are hard?
are the hardest natural material. A diamond is a mineral. Diamonds are rare. They are also gemstones because they make sparkling jewellery when they are cut. Diamonds are also used in factories to cut and grind down other materials. These diamonds are small and are manufactured materials. It is not possible to manufacture the size of diamond that is used as a gemstone.
Are teeth made from a hard material?
Yes. It is called enamel and is the hardest substance in your body. Enamel makes the white surface of the teeth. It needs to be very hard because it receives a great deal of wear as your teeth cut up and crunch and grind your food. However, it is not as hard as stone or metal. This is why you always have to be careful not to bite on even harder materials. In time, teeth do begin to wear away, even when just used for eating food. In the past teeth wore away very fast because people ate food which still had some soil and other gritty bits in it.

What are the softest materials in the home?
The softest materials include talcum powder in the bathroom, graphite in a pencil and butter.

Talcum powder is made from a mineral called talc. Talc is so soft that when you touch it, your fingers feel like they are touching slippy soap. Talcum powder is made up of tiny flakes of talc. They are rubbed on the skin to dry it because talc is soft and soaks up water. Talc does not damage the skin because it is softer than the skin. Think what might happen if something as hard as sand was used to dry the skin.
Does your skin wear away?
Dead skin is flaking off all the tine as it rubs against your clothes. It makes much of the dust in a room. The flakes are so small that you need a microscope to see them.
Your skin does not wear out because new skin grows as fast as the old skin is lost.
We say cushions and pillows are soft. Is that wrong?
Although we might say that the surfaces of cushions and pillows feel, they are NOT actually made from soft materials. If they were they would wear away quite quickly. The properties of the cushion that makes us call it soft are the flexibility of the cover and the springiness of the filling material inside.
When you lay your head on a pillow the filling squashes and the cover bends to follow a new shape. The actual fibres in the cover of the pillow are quite hard and do not flake off as your skin rubs against them. In fact, your skin flakes off as you rub against the pillow, so after a short time your pillowcase needs washing to remove your skin flakes!