Materials

an investigation into different materials can prove both stimulating and fun, and this topic offers enormous scope for creative teaching. With this in mind, this issue of Teaching & Learning has adopted the theme of materials for its own Key Stage 1 and Key Stage 2 Creative Teaching section. As with other issues, we have included a set of lesson plans for literacy, numeracy and science – all stimulated (and driven) by materials science.

What is a material?

A material is a substance that has specific properties – it is a tangible substance that goes into the makeup of a physical object. The properties of a material are defined by the arrangement of the atoms or molecules in the substance. A raw material is a material that comes directly from nature in an unprocessed form. Raw materials include clay, wood, wool fleece and some metals. Processed materials (as the name suggests) have gone through some sort of manufacturing or production process, which alters their natural state but not their properties. Processed materials include bricks (which are produced by processing clay); paper (which is produced by processing wood); and steel (produced by processing iron).

What is an object?

An object is an item that has been designed, processed or manufactured to serve a specific purpose or function. Objects are different to materials and can be made from one or more different materials. The materials used to produce an object are selected according to their specific properties and how those properties meet the objects’ requirements. Examples of objects include pencils (made from graphite and wood) and tables (made from wood, plastic and/or metal).

Materials or objects?

Sometimes it is difficult to determine whether something is a material or an object. But if you remember the following you shouldn’t go too far wrong:

1. If something (item A) is used to create something else (item B) (such as wood being used to make a table), then item A is a material and item B is the object.
2. If something (item A) does not undergo further processing and is used in its natural state, then it is a material.

Materials vocabulary

Each material has its own set of properties. A property describes something about that material and the things it can and can’t do. When testing materials for properties, precise vocabulary must be used, especially as many of the words that will be used to describe the properties of different materials are frequently used in everyday speech. Here is a table with some vocabulary associated with materials, clearly defined:

There are, of course, other items of vocabulary that pupils should learn to use appropriately and effectively, including:

• Words to describe properties: hard, soft, strong, weak, tough, brittle, stiff, rigid, flexible, absorbent, waterproof, magnetic, non-magnetic, wear and tear, smooth, rough, transparent, opaque and translucent.
• Names of a variety of materials: wood, metals (copper, tin, steel, gold, silver, aluminum and chrome), plastic (polythene, polystyrene and PVC), fabrics (cotton, silk, polyester, wool and acrylic), foam, glass and rubber.

There are many different types of materials, including wood, glass, metals, plastics, fabrics, ceramics etc. However, we cannot cover all of them, so we have only included some basic information on wood, glass, metals and plastics.

Wood

Wood is an incredibly useful naturally occurring material. Throughout the centuries, enormous structures have been built using wood because it has a number of remarkable properties.

Useful properties

Wood has the following useful properties:

• Wears well
• Durable if kept dry
• Very strong for its weight
• Quite easily worked
• Can be steam-bent into tight curves
• Repairable
• Warm to the touch
• A reasonably good insulator for both electricity and heat

Not so useful properties

Wood has the following not-so-useful properties:

• Wood burns, although it is not excessively flammable.
• When wood is burned, it releases a variety of pollutants
• Wood rots if left in contact with the earth
• Wood cannot be cast, moulded, or extruded.
• Shrinks and swells with changes in humidity.

Uses of wood

Wood is so widely used that a full list of its uses is impossible to compile. Uses include shipbuilding, house building, roofing, fences, railway sleepers and furniture.

Conserving wood supplies

As a naturally occurring material, wood is not limitless. We are using more than we are growing. Wood is very much abused and taken for granted. It is used in many things only to be discarded (such as packaging) and this means that great swathes of forests are chopped down for no real reason. Many uses that wood is put to could easily be accommodated with other materials. One of the main uses of wood is for paper and the world uses millions of tonnes of wood to make paper for books, magazines and newspapers – with many of these items ending up in the dustbin. Paper can be made from other fibres and paper should always be recycled.

Metals

Metals are extremely versatile and a huge variety of metallic elements are listed in the Periodic Table (more than 70).

Useful properties

Metals have the following useful properties:

• Resistant to flames – will not burn.
• Long-lasting, hard and durable.
• Strong but malleable – can be easily shaped into structures.
• Excellent conductors of both heat and electricity.
• All metals absorb light at all frequencies and immediately radiate it, this allows them to reflect and shine (for example in mirrors).
• Metals emit electrons when exposed to radiation (e.g. light) of a short wavelength or when heated to sufficiently high temperatures. This property is exploited in television screens and a variety of electronic devices and instruments.
• Metals, like lead, can absorb radiation.

Not so useful properties

Metals have the following not so useful properties:

• Metals can sometimes conduct electricity when you don’t want them to!

Uses of metals Metals (along with wood) are widely used in the construction and manufacturing industry. There are so many uses for metals that it would be impossible to list them all here, but any look around a classroom or home will throw up lots of objects that have some sort of metal component.

Conserving metal supplies

Because metals (such as aluminium) take a long time to degrade (break down) they should never be just thrown away and should always be recycled. The most common metals we need to consider when discussing recycling are aluminium and steel. Some other metals –like gold, silver, brass, and copper – are so valuable that they are rarely thrown away. It is estimated that Western societies use more than 100 million steel cans and 200 million aluminium drink cans every day. This amounts to a vast mountain of used metal, and if we don’t want the world to end up as a refuse site, something has to be done with all that waste. While it is important to use less metal in the first place (particularly in drinks cans and packaging), recycling is the most efficient way to reduce aluminium and steel waste.

Glass

Glass is a manufactured material formed when a mixture of sand, soda, and lime is heated to a high temperature and assumes a molten, or liquid, state. Unlike most other materials, it does not form crystals as it cools. Instead, it becomes a ‘super-cooled liquid’, behaving not unlike toffee and resisting any change in the arrangement of its molecules. This means that glass can be manipulated while hot to form any shape desired and will retain that shape as it cools.

Useful properties

Glass has the following useful properties:

• Transparency – glass lets light through easily
• High melting temperature, so can withstand a lot of heat
• Low density so is light
• Strong and stiff
• Hard wearing
• Resistant to corrosion

Not so useful properties

Glass has one major drawback – it is brittle! Uses of glass Glass has historically been used for low-technology applications such as drinks bottles and windowpanes. However, glasses have recently been used in high technology fields, particularly the semiconductor microelectronics industry where silica is widely used as an insulator in transistors and the fibre optic cable industry, where high-purity silica glass has made advanced telecommunications possible.

Conserving glass supplies

As with metals, if we do not recycle glass (which does not break down easily) we will end up with miles of refuse dumping sites, the raw materials used to produce glass will become more and more expensive and supplies will reduce.

Plastics

The term ‘plastics’ covers a range of man-made (synthetic or semi synthetic) materials that can be moulded or extruded into objects, films or fibres. Their name comes from the fact that in their semi-liquid state they are very malleable. While they vary in heat tolerance, hardness and resiliency, all plastics are very adaptable, which has resulted in them being used in thousands of different ways. Many new developments just would not be possible without plastics.

Useful properties

There are thousands of different types of plastics, but in general they have the following useful properties:

• As a material, plastic is safe and hygienic
• Flexible and easily adaptable to suit a range of specifications
• Lightweight
• Plastics are tough and durable (capable of being used again and again)
• Adaptable
• Good insulators

Not so useful properties

Disposing of plastics has to be carefully done – some plastics release toxic fumes when burnt and all plastics take a long time to degrade, so should always be recycled.

Uses of plastics

There are literally thousands of possible uses of plastics. The clothes we wear, the houses we live in, the cars we drive, packaging for our food, computers, televisions, music CDs… the list is endless. Recycling plastics While modern-day plastics use only minimal amounts of oil (with oil being a valuable and finite world resource), it is still essential that they are recycled and not merely discarded. However, the recycling of plastics is more problematic than glass or paper. Of all the materials that can be recycled, plastic is the most difficult due to its high volume and light weight. This makes it very expensive to collect and transport. In addition, the market for plastic for reprocessing is limited to a few specific types of plastic bottle.

The three Rs

Millions of tonnes of waste get thrown away every year – and it all has to go somewhere. Invariably it ends up in landfills, but if the world just kept throwing everything into landfills, then we would soon run out of land! This is a fact that everyone can understand, yet many people still do not regularly recycle. Schools now teach the three Rs: Reduce, Reuse, Recycle.

• To REDUCE is to buy fewer things, so that we have less garbage do contend with. Reducing is the most effective way to cut down on municipal solid waste.
• To REUSE means not to throw things away after having used them only once or twice.
• To RECYCLE is to take items to a recycling place for them to be reprocessed and used again.

Resources

Materials Project Plan Poster (Open Access)

Materials Project Plan Literacy Resources

Materials Project Plan Literacy Numeracy Resources

Materials Project Plan Literacy Science Resources

References

www.chemsoc.org/pdf/learnnet/nc/tc_nc1.pdf www.jhcrawford.com/energy/wood.html Department of Materials Science at Cornell University

Did you know…

1. When glass breaks, the cracks move faster than 3,000 miles per hour.
2. Each year, an estimated 500 billion to 1 trillion plastic bags are used worldwide. This is more than one million per minute.
3. Scientists believe that there may be 70 million tonnes of gold in the ocean – but no one has (as yet) worked out a way of getting it!
4. Paper is the most common thing in a refuse dump. About 40 per cent of an average dump is paper, all of which is recyclable!
5. Each time a piece of paper is recycled, 20 per cent of the fibres are lost – so most paper can only be recycled five times.