Introduction to materials

Philip and Kim are working on a project for science class. They want to make a model of a city on another planet. To build it, they are planning to use styrofoam, cotton wool, paper, aluminium foil, glass bowls, plywood, sand, plastic bags and more. These are substances used to make other objects — they are materials. There are many different types of materials, and when we study them, we often place them into groups.

One way to classify materials is to group them as either natural or human-made, artificial. Natural materials are those that can be found in nature, such as cotton, wood, and sand. Artificial materials do not occur naturally. Instead, they are designed and manufactured by humans. Some examples include styrofoam, plastic, and paper.

Another way to group materials is based on whether they come from living or non-living things. Paper, for instance, is made from plants that were once alive. It is an example of an organic material. Other examples of organic materials include leather from cows’ skin or wool from sheep. Plastics are also considered organic materials because they are made from petroleum, which formed millions of years ago from once-living organisms.

Materials that come from non-living things are known as inorganic materials. These include minerals and rocks — such as quartz that makes up sand — as well as metals, such as aluminium. Materials can also be grouped depending on their composition. This way, materials are often divided into metals, polymers, and ceramics. Metals are materials composed of metallic elements such as aluminium, gold, iron, or nickel.

Mixtures of those metallic elements — alloys — such as steel, bronze, and brass, also belong in this category. Depending on whether they contain iron or not, metals can be further divided as either ferrous or non-ferrous. Polymers are made up of very long chains of molecules. Some polymers occur naturally, for instance, cellulose in wood and cotton, or protein polymers that make up silk and wool. Others, such as those that make up synthetic rubber, styrofoam, and different types of plastics, are manufactured by humans.

Ceramics are a group of inorganic and non-metallic materials that are hardened by firing at high temperatures. Glass and clay are examples of materials often put into this category. Finally, there is one more group of materials made by combining two or more different materials, so that one acts as a binder and another acts as a reinforcement. Such materials are called composite materials or composites. Some common examples of composites include plywood — made from layers of wood bound by glue — and fibreglass, in which small fibres of glass are embedded in a polymer.

All materials have different characteristics, such as colour, hardness, or flexibility. We call these properties of materials. Materials within the same group usually share several properties. Most metals, for instance, are solid at room temperature, have a shiny surface, and conduct electricity very well. But every material has its own individual properties as well, meaning some are better-suited for certain uses than others.

When it comes to Philip and Kim’s project, plywood, which is hard and stiff, will likely be a better base than paper, which is much softer and more flexible. But, paper is easier to scrunch and colour, so it may be the best material to imitate the rough surface of another planet! Knowing the materials and their properties allows us to use them to make things exactly how we want them to be.