MATERIALS

Any substance that is used to make something is a material. Natural materials such as stone and wood are used as they are found in nature. SYNTHETIC materials are made from natural materials with the help of heat and chemical reactions.

WHAT ARE MATERIALS’ PROPERTIES?

Materials are selected for use according to their properties (characteristics). Mechanical properties, such as strength, are important for materials used in construction. Chemical properties show if a material will react with other materials. Thermal properties show how a material conducts heat.

HOW STRONG IS A SPIDERWEB?

Millions of years of evolution have produced natural materials ideally suited to the jobs they do. A spider’s web is, weight-for-weight, 10 times as strong as steel, and far more elastic. Bones, teeth, and tusks are also very strong natural materials. They can be used every day for a hundred years without breaking.

HOW ARE MATERIALS USED?

The chosen materials for a product need to be shaped and put together. Wood is shaped by sawing, planing, and drilling. It is joined with nails, screws, or glue. Metal is bent and hammered into shape—or heated until it melts, and poured into molds. Metal is joined with nuts and bolts, rivets, or by welding.

SYNTHETICS

A substance made artificially, by heat and chemical reactions, is a synthetic. It may be similar to a natural material, or have completely new properties.

WHAT WERE THE FIRST SYNTHETICS?

Heat melts sand and other minerals to make glass. The first glass bottles were made about 3,500 years ago in Ancient Egypt. The first modern synthetic was made in 1909, when Leo Baekeland, an American chemist, created a plastic called Bakelite.

WHAT IS A COMPOSITE MATERIAL?

Composite materials combine the useful properties of two or more materials in one. Steel is strong and concrete is strong, but steel-reinforced concrete is even stronger. It is used for constructing tall buildings and long bridges.

Copyright © 2007 Dorling Kindersley