Subject Facts

Defining 'materials'

All matter, that is everything around us — objects, animals, plants, the ground, the air — is made from materials. There are many, many different types of material and many of those are in a constant state of change, either changing from one type of material to another, or changing their state (between solid liquid and gas). Plants, using sunlight as an energy source, turn a gas (carbon dioxide) and water into solid vegetation, which animals then eat before dying and decaying, releasing the carbon back into the environment once more. The nature of materials is like a construction kit — the same small pieces (atoms) can be rearranged to construct many different objects (compounds).

Look around you. Consider the different objects you can, see and the different materials from which they are made. It is important to separate objects from materials: an object (a pen) may be made of several distinctly different materials, while one material (steel) may be used to make several distinctly different objects. In the same way that children learn to define what, for example, a ‘chair' is, and how it is distinct from a 'table', through continuous and increasingly precise use of the terms, they can begin to sub-categorise chairs into different types (stools, sofas, thrones .. ) by repeated usage. In a similar way, knowledge of materials can become increasingly more precise. We define all that is around us by agreeing the set of characteristics that distinguishes, for example, a 'metal' from a 'wood'. It is sometimes possible to confuse the issue when either imprecise or conflicting definitions are given or there is a confusion between object and material. We must always be precise and ensure that when we are talking about 'material', we are focusing on what it has been made from not what it has been made into.

Describing materials

There are several groups of adjectives that are commonly used to describe materials, depending upon the senses or tests being used. These terms might relate to the texture, strength or optical qualities or one of a number of testable characteristics such as electrical conductivity. A material is recognised by the collection of known characteristics that it possesses.

If we examine the material 'glass', for example, we must start by focusing on the material rather than an object of the same name. A 'glass', though often made of glass, is often the name given to a drinking vessel without a handle (though sometime beaker' is used). 'Glasses', that is, spectacles, frequently have no glass content at all. So what characteristics spring to mind when you think of the material glass'? Transparent, brittle, hard..?

Polystyrene is a clear plastic that is often used as an alternative to glass (particularly for drinking vessels). (As an aside, if you are wondering about those 'polystyrene' cups from hot drink vending machines or the packaging material — this is expanded polystyrene: rigid foam made of polystyrene and air.)

How can you distinguish between polystyrene and glass? Well, glass is denser — of two identical 'glasses' the plastic one will be lighter. glass shatters more readily than the plastic but is more resistant to scratching — hardly constructive though is it? Neither is it particularly helpful to test by seeing which one melts first when exposed to high temperatures (it's the plastic). Try tapping both materials with something hard — a coin or even a fingernail — the glass will give a much clearer; sharper sound than the polystyrene. Why? — because of the structure of the material (and that's what most of this section is about, so read on).

Materials are also frequently described in terms of where came from, particularly whether they were found naturally or whether they have been manufactured for example, in clothing indicate the source of the fibres (and often the proportions in which they have been used).

Object and material

It is often quite easy to confuse the property of the material with the property of the object into which it has been made. A material may be dense, but an object would be described as heavy (in terms of mass). The distinction between the object and the material must be highlighted at each stage of work with the children. When comparing materials, the object issue can be avoided to a very large extent if standard samples (size and shape) are used. Frequently objects are made from a combination of more than one material, to make the best use of the individual characteristics of each – this can also cause confusion when testing or observing objects in place of materials. Material samples need to be uniform.

Why you need to know these facts

The word 'material' has many different meanings, which are determined by context. An underdstanding of this key terminology and the different types of material is fundamental to furtehr work in this area of science.

Vocabulary

Atom — the smallest 'lump' of an element.

Compound — a material made from different atoms chemically blended together in precisely the same proportions throughout.

Element — a material made from only one type of atom.

Common Misconceptions

Material is fabric

This is another wexample of he problems caused by the imprecise use of English in common usgae. To rectify the misunderstanding, children need to be reminded that particualr words have a more specific meaning when they are used in the context of sciecne (jus like 'animal')

Questions

Why can't you use words like 'heavy' to describe a material?

because words like 'heavy','big, or 'bendy' depend more upon the size and shape of the piece of hte material than the material itself. A large block of glass, for example, would be big, heavy and rigid but fibre optics (the same material) would be small, light and bendy.

Teaching ideas

word lists (research, recording)

in groups or as a class, the children can prodcue lists of adjectives to be used to describe materials and objects. Discussions will need tro take place to decide whether the words realte more appropriately to materials or objects that can be made from different materials.