Black foam rubber. This feels stretchy and has lots of grip like real rubber but it is another type of plastic foam made from special chemicals which come from oil.

Odd ones out

The elastic band and balloon are made from rubber (latex) which comes from a tropical tree. Should they be in the ‘wood’ group?

Wood
Hardboard, cork, wooden dowel, wood strip and paper.
The paper doesn’t look or feel the same as the others in the group but paper is made from wood pulp. Sometimes the properties of a material change as it is processed into something new.
Cork is the bark of a ‘cork oak’ tree.
Generally speaking wooden materials are not very hard (we can cut them with tools fairly easily) and are lightweight. They are a dull yellowy brown in their natural state.

Metal
Steel, copper, aluminium, brass, aluminium foil (cooking foil), steel bolt, brass paper fastener, steel paper clip, copper coin.
Metals are shiny and very strong. Most are heavyweight materials although aluminium is unusually lightweight (good for making aeroplanes). Aluminium foil is very thin like paper but it doesn’t have the same feel, texture or appearance.
Metals all feel cold to the touch although a small piece quickly warms up in your hand and so this isn’t always noticed.

Plastic
Plastics can cause a lot of confusion because they can be in so many different colours and types. They can be transparent, translucent or opaque. They can be lightweight or heavyweight although most types are lighter than metals.
They can be soft, hard, stretchy, flexible or strong although not as hard or strong as metals.
Plastics feel slightly warm to the touch although this can be difficult to observe.

Fibres and Fabrics
These are all made from tiny threads called fibres. They can be from plants like the cotton plant or from animals (wool from a sheep or silk from a silk worm). They can also be man made from chemicals. Nylon is a man made fibre and so is polyester.
Fibres are very important for clothing but they are also needed for making all sorts of other important things such as ropes and sails for ships. The silver-grey cloth in this picture is fire-proof and can be used if fire-resistant clothing or in the walls and rooves of buildings to prevent fire spreading.

Stone and Glass
These materials don’t appear to be related. Glass is transparent but pottery and stone aren’t. Glass is made from sand and sand comes from rock which has been worn down by the action of the waves and weather. Glass is made by heating sand and other minerals from the earth to a very high temperature. It melts and forms glass. Glass can be found in the earth near volcanoes. Pottery and glass are often called ‘ceramics’. Ceramic materials are very hard and can resist high temperatures. The broken clay pot in the picture is very fragile because it has yet to be put in a hot oven to bake it hard and become like a ceramic material.

Wood has been used as a building material for houses, forts, ships etc. for many thousands of years. It is lightweight yet strong and floats in water. Some types of wood are strong and springy and can be used to make a bow to fire arrows.
Wood can be shaped with tools and is a very good insulator of heat so it feels warm inside a wooden house.
What are the strange lines and features found in wood? On the end of a piece of wood you can often see curved lines. How did the curves get there?

Metals make a clinking clanking sound. We say that metals are ‘sonorous’. This means that they make a sound when struck. Church bells are made of metal for this reason. If it wasn’t for this special property of metals we wouldn’t have many musical instruments.

Heaviness of materials can be difficult to judge so we have to be careful and make a fair test when comparing the different materials.
Here are pieces of plastic, wood and metal which are all the same length. The stick of plastic is the heaviest but this is because it is a much thicker piece than the others. In order to make it fair we would have to choose pieces of material which were the same size all over.

Here are sticks of wood, metal and plastic which are identical in length and thickness. They are truly the same size.
If we simply hold one at a time we can quickly work out which is the heaviest.
The metal rod is heaviest. The wooden rod is lightest and the plastic rod is between the two.
Scientists compare heaviness by using the word ‘density’. The steel rod in the picture is more dense than the plastic rod. The plastic rod is more dense than the wooden rod. Density depends on the mass of a material compared to it’s size (volume).

Metals are very useful. There are about 90 different metals and lots more ‘mixed metals’ or ‘alloys’. Copper is orange/brown in colour (actually it is bright pink when first formed) and it is a pure metal but brass is a yellow/gold colour and is an alloy or mixture of copper and zinc. Bronze is an alloy of copper and tin. Aluminium is a very special low density metal used in making aeroplanes and lightweight engine parts for cars etc.
Which is which - aluminium, steel, copper, brass?