Wood is one of the widely used materials in the world. In this lesson, we will learn about:
Wood is an organic material, which means it comes from nature. It is a hard fibrous structural tissue found in the stems and roots of trees and other woody plants. If you cut through the trunk of a tree, there are several rings that tell you how old the wood is. The more rings the tree has, the older the wood.
It has been used for thousands of years for both fuel and as a construction material, for making tools and weapons, furniture, and paper. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin that resists compression.
Take a tree and peel off the outer "skin" or bark and what you'll find is two kinds of wood. Closest to the edges there is a moist, light, living layer called sapwood packed with tubes called xylem that helps a tree pipe water and nutrients up from its roots to its leaves; inside the sapwood, there is a much darker, harder, part of the tree called heartwood, which is dead, where the xylem tubes have blocked up with resins or gums and stopped working.
Around the outer edge of the sapwood (and the trunk) is a thin active layer called the cambium where the tree is actually growing outward by a little bit each year, forming those famous annual rings that tell us how old a tree is. Cambium is often only one or two cells thick, and you need a microscope to see it well.
Slice horizontally through a tree, running the saw parallel to the ground (perpendicular to the trunk), and you'll see the annual rings (one new one added each year) making up the cross-section. Cut vertically through a tree trunk and you'll see lines inside running parallel to the turn formed by the xylem tubes, forming the inner structure of the wood known as its grain.
You'll also see occasional ovals interrupting the grain called "knots" which are the places where the branches grew out from the trunk of a tree. Knots can make wood look attractive, but they can also weaken its structure.
If you look at some freshly cut wood under a microscope, you'll see it is made up of cells, like any other plant. The cells are made of three substances:
Broadly speaking, cellulose is the fibrous bulk of a tree, while lignin is the adhesive that holds the fibers together.
Hardwood
Hardwood comes from angiosperm trees, which are plants producing flowers and bearing seeds in fruits. It tends to come from slow-growing, deciduous trees which lose their leaves annually. The wood is usually heavy, tough, and denser. Hardwoods often have additional channels for transporting sap, known as vessels or pores. These may be visible to the naked eye, or under magnification, as tiny pinholes when the wood is cross cut. As a result of their condensed and more complex structure, hardwoods generally offer a superior level of strength and durability. Common types of hardwoods include oak, maple, cherry, mahogany, and walnut.
Hardwood species are not always necessarily stronger than softwoods, but many species are well known for their beautiful and distinct wood grain patterns.
Softwood
Softwoods are normally derived from coniferous trees, that is, trees with needle-like leaves and whose seeds are covered in cones. These are fast-growing trees, producing soft and light wood. Pines, spruces, larches are familiar examples. The exception to the rule is yew, which is both slow-growing and very dense.
Confusingly, some softwoods are harder than hardwoods!
Softwoods don’t normally have visible pores. Rays also may be narrow or virtually invisible. Softwoods can sometimes be identified by the presence of resin, or a ‘turpentine’ smell, particularly when freshly cut.
| Characteristic | Hardwood | Softwood |
| Originates from | Deciduous trees | Evergreen trees |
| Examples | Oak, Teak, Mahogany | Pine, Spruce, Fir |
| Price | More expensive | Less expensive |
| Density | Typically harder (but not always) | Usually softer (but not always) |
| Color | Generally dark | Almost always light |
| Structure | Lower sap | Higher sap |
| Grain | Close | Loose |
| Fire resistance | Good | Poor |
| Weight | Heavy | Light |
The chemical composition of wood varies from species to species but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantities.
Strength
Physically, wood is strong and stiff; however, compared to materials like steel, it is also light and flexible.
Metals, plastics, and ceramics are isotropic i.e. they have a fairly uniform inner structure and they tend to behave exactly the same way in all directions. Due to its annual ring and grain structure, wood acts differently.
Have you ever tried to chop wood with an ax? If you have, then you would know that it splits easily when sliced with the blade along with grain, but is much harder to chop the opposite way through the grain.
Take a small, dead, tree branch. Try to bend and snap it with your bare hands. Can you do it? YES.
Now, try to pull or push it in the opposite direction. Can you stretch or compress it? NO.
This means wood is anisotropic, which means a lump of wood has different properties in different directions.
Durability
Wood lasts quite a long time. Ever heard of archeologists unearthing the buried remains of ancient wooden sculptures or tools that belong to a civilization existing hundreds or thousands of years ago? A once-living thing, wooden objectives are subject to natural forces of decay through a process known as "rotting" - in which organisms such as fungi and insects such as termites and beetles gradually nibble away from the cellulose and lignin and reduce wood to dust.
Wood and water
Wood is hygroscopic, which means just like a sponge, it absorbs water and swells up in damp conditions, giving out the water again when the air dries and the temperature rises.
Wooden windows open much more easily in summer than in winter. Do you know why? Too much humidity does this. The damp outdoor conditions in winter make them swell into the frames.
Why does wood absorb water? Remember that the trunk of a tree is designed to carry water from the roots to the leaves. A freshly cut piece of "green" wood typically contains a huge amount of hidden water, making it very difficult to burn firewood without a great deal of smoking and spitting. Some kinds of wood can soak up several times their own weight of water, which is absorbed inside the wood by the very same structures that transported water from the roots of the tree to the leaves when the tree was a living, growing plant.
Wood and energy
Wood is a good heat insulator but dry wood does burn quite easily and produces a great deal of heat energy if heated up beyond its ignition temperature (the temperature at which it catches fire, anywhere around 200–400°C, 400–750°F).
Generally, wood is good at sound absorption because it's porous, with plenty of air spaces to trap sound. However, wood isn't dense enough material to absorb much sound as is. On the other hand, wooden objects are also designed to transmit and amplify sounds - that's how musical instruments work.
Wood doesn't conduct electricity. However, when the wood is wet, then its conductivity increases.
1. Fencing and decorating gardens
Wood is used in the fencing and decorating of gardens as it makes it look the whole garden open and still protected.
2. Used in producing furniture
As we know, all the furniture in our homes is made out of wood. Our chairs, tables, shelves, and others are all constructed with wood and still designed.
3. Used in creating art
Wood is used in the creating and designing of all art-related stuff. That includes sculptures, carvings, and art frames that we place in our home.
4. Used as insulation
Wood is a better insulator than most equipment because of its nature. It is used to measure the insulation properties of building materials. It has this ability due to the air pocket within its air structure.
5. Used for heating
Wood is a good source of energy when used with fuel. It can be used for heating in the forest as a campfire. It can also be used in an indoor furnace to keep the rooms warm to avoid cold.
6. Used to make most kitchen utensils
Most kitchen utensils are made of wood because of its insulating ability. The handles of the kitchen utensils, when made with wood, would prove to be of better handling as people wouldn’t be scared of getting hurt due to the hotness of the handles.
7. Used to make musical instruments
This is one special and beneficial use of wood in the modern age. Wood is used to make almost all musical instruments like piano, guitar, drum, and a lot more.
8. Used to make Sports equipment
Wood is one of the essential material used in making sports equipment like in cricket, table tennis, and hockey.
9. Used in shipbuilding
Wood is another important material when it comes to the making of ships. Both large and small ships are made of wood as it helps in buoyancy.
10. Used to make children's toys
children’s toys are made up of wood. Today, parents do prefer to buy wooden toys for their kids as they consider plastic toys harmful due to its toxicity.
