４年生(Eネイティブ)理科
Natural Sciences and Technology Grade 4-A
Matters and Materials
Chapter 2. Solid materials p.160
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ブルーの色を付けた文章、ぜひ参考にしましょう。
2.3 Properties of materials
Raw and manufactured materials have specific properties. We already looked at some of the properties of raw and manufactured materials by describing them. The properties of a material help determine how it is used. For example, plastic is waterproof so some rain jackets are made of plastic to keep the rain off and keep you dry. A rain jacket made from wool or fibre would not be waterproof and you would be soaked! This is because the wool is an absorbent material (it absorbs water).
Hard or soft?
A material is described as hard when you cannot scratch it, you cannot cut it and you cannot dent it. Hardness measures how diffcult or easy it is to change the shape of the material, either by denting, cutting or scratching it. A diamond is an example of a hard material as diamond cannot be scratched by other objects. In fact, diamond is so hard it is used on drill bits to drill through rocks and many other materials The opposite of hard is soft! Think of the wet, raw clay from the previous chapter. This clay is soft and can therefore be moulded into a new shape.
このようなテキストに中高生で触れることができれば、理工学部に進学する生徒さんは楽になりますね。
hard、softに対して toughnessの説明(p.163) は次のようになっています。
If you hit a metal coin with a hammer, there will be no or little damage. If you hit a piece of chalk with a hammer it will break into pieces. The metal coin is tough compared to the chalk. The chalk is very fragile.Toughness measures how much energy is needed to break a material.
