Properties of Materials: Wood – JSS1 Basic Technology Lesson Note (First Term)

Wood is the hard, fibrous material found beneath the bark of trees and bushes.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the materials used in technology;
2. list the parts of the internal structure of wood and state the function of each;
3. list the major external parts of a tree;
4. state the two classes of wood and give examples of each;
5. differentiate between hardwood and softwood;
6. mention at least five uses of wood.

What are the materials used in technology?

The materials used in technology are wood, metals, ceramics, rubbers and plastics.

• Wood: hard, fibrous material from trees, used for furniture, doors and building.
• Metals: strong materials such as iron, copper and aluminium, used for tools, wires and roofing sheets.
• Ceramics: baked clay products such as pots, tiles and bricks.
• Rubbers: stretchy materials used for tyres, hoses and shoe soles.
• Plastics: light, moulded materials used for buckets, chairs and electrical casings.

Each material has its own properties, so each is suited to a different job.

What is wood?

Wood is a hard, fibrous substance found chiefly in trees and bushes, beneath their bark.

• Source: tree trunks are cut into wood, also called timber.
• Main uses: furniture making and building construction.

Different types of wood are identified by:

• Colour: some woods are dark and some are light.
• Class: wood is grouped into hardwood and softwood.
• Leaves of the tree: hardwood trees have broad leaves, while softwood trees have needle-like leaves.

What is the internal structure of wood?

The internal structure of wood is made up of six parts: pith, xylem, cambium, phloem, cork cambium and bark.

1. Pith: the soft core at the centre of the trunk.
2. Xylem: the layer that carries water and minerals up from the roots and forms the wood we use.
3. Cambium: a thin layer of living cells that makes new xylem and phloem, so the trunk grows wider.
4. Phloem: the layer that carries food made in the leaves to other parts of the tree.
5. Cork cambium: a thin layer that makes the cork cells of the outer bark.
6. Bark: the outer covering that protects the tree from injury, insects and loss of water.

What are the major parts of a tree?

The major external parts of a tree are the roots, trunk, branches, leaves, flowers and seeds.

1. Roots: hold the tree in the soil and take in water and minerals.
2. Trunk (stem): supports the tree and carries water and food. It is cut into timber.
3. Branches: grow out of the trunk and carry the leaves.
4. Leaves: make food for the tree using sunlight.
5. Flowers: produce the seeds, in trees that flower.
6. Seeds: grow into new trees.

• When a tree is left to grow for a long time, its trunk becomes thicker and the tree grows taller.
• Trees are of different sizes: some are big and some are small.

What are the classes of wood?

There are two classes of wood: hardwood and softwood.

• Hardwood: wood from broad-leaved trees, usually dark and heavy.
• Softwood: wood from needle-leaved, cone-bearing trees, usually light in colour and weight.

The names describe the type of tree. They do not always describe how hard the wood is.

What are the properties of hardwood?

Hardwood is wood from broad-leaved trees, and it is dark and heavy.

1. It is dark in colour.
2. It is gotten from deciduous trees.
3. It has a complex cellular structure.
4. It is heavy.
5. Its annual rings are not clearly visible.
6. Hardwood trees have broad leaves.
7. Examples include Iroko, Afara, Mahogany, Opepe and Omo.

• Uses: furniture making and building construction.

What are the properties of softwood?

Softwood is wood from coniferous trees, and it is light in colour and weight.

1. It has a lighter colour than hardwood.
2. It is not heavy.
3. It is easy to work on.
4. It is gotten from coniferous trees.
5. Softwood trees have narrow, needle-like leaves.
6. Softwood trees are usually evergreen because they do not shed their leaves in the dry season.
7. Examples include spruce, pine, cedar and cypress.
8. These trees bear naked seeds in cones.
9. These trees grow better in a temperate region (a cold region of the world).

What is the difference between hardwood and softwood?

Hardwood comes from broad-leaved trees and is dark and heavy, while softwood comes from cone-bearing trees and is lighter in colour and weight.

What are the uses of wood?

Wood is used in housing, building, joinery, packaging, furniture, transport, bridges, paper, medicine, clothing and tool making.

1. Housing: doors, windows and roofing in homes.
2. Industrial building: many industrial structures are built with wood.
3. Joinery: staircases and other fittings in buildings.
4. Packaging: crates, pallets and cases for packing electronic equipment.
5. Furniture: chairs, beds, wardrobes, tables and bookcases.
6. Transport: railway wagons and lorry bodies.
7. Bridges and poles: farm bridges and village road bridges, some electric poles and railway sleepers.
8. Pulp and paper: exercise books, textbooks and magazines are made from wood pulp.
9. Medicine: some artificial limbs for people who have lost an arm or leg are made from wood.
10. Clothing: some shoe heels and soles are made from wood, and rayon fabric is made from wood pulp.
11. Tool making: handles for hammers, pickaxes, felling axes and screwdrivers.

Evaluation

1. Mention the materials used in technology.
2. Draw the internal structure of wood and label its parts.
3. Differentiate between hardwood and softwood.
4. Mention five (5) uses of wood.

Assignment

List the major external parts of a tree, then name three examples of hardwood and three examples of softwood.