Physical and Mechanical Properties of Wood in Physics
Wood is the second most used material for construction purposes, making of furniture, flooring, etc. For building constructions, though the stone has taken first place, the boom of wood has increased dramatically in recent times. Let's see more interesting facts about wood, different physical, chemical, mechanical, properties of wood.
Tissue Composition of Wood
Wood is a natural resource that can be obtained by plants and trees. Basically wood is a combination of different tissues like the xylem, which is a vascular tissue, phloem, and cell walls. The vascular cambium layer which is present inside the bark helps to produce new wood.
Properties of Wood
The properties of wood explain its behaviour, and how it reacts to different substances at different temperatures. These properties explain the characteristics of wood with a generalized meaning. The properties of wood may include physical properties, chemical properties, mechanical properties. The physical properties of wood can be defined as the characteristics of a wood that do not have any change in its size, shape, colour, etc.
Physical Properties of Wood
The characteristics of wood that explain the physical features of various types of wood are nothing but the physical properties of wood. They are explained as follows.
Colour - As the basic use of wood is to make furniture and decor items for the house, colour and appearance play a vital role in choosing a variety of wood. But the colour of the wood varies from type to type. The wood is available in a wide range of colours starting from white to dark brown etc. The colour of the wood also changes with the observation. If a tree can be observed from top to bottom, it appears in some colour and vice versa.
Lustre - Another physical property of wood is its lustre. Luster refers to the tendency of elements with the reflection of light. After colour, priority is given to the lustre of the wood.
Odour and Taste - We commonly observe different odours from different types of wood. For example, the sandalwood and the rosewood give a nice aroma whereas the other timber woods may give some tobacco odour. Also, the new wood sample gives a fresh aroma and it keeps on degrading with time.
The density of Wood - Another characteristic of wood is its density. But what is the density of wood? The density of wood refers to its mass per unit volume. Based on the weight of the wood sample, the density of wood changes. Different types of wood have different densities. Below detailed information about the density of different types of wood is given.
If the density or specific gravity is 36 then the wood is called very light.
When density or specific gravity is = 0.36 then the wood is called light.
If the density or specific gravity is 0.36 – 0.05, then wood is considered moderately heavy.
When density or specific gravity is > 0.05, then the wood is heavy.
Hardness - Hardness refers to the strength of the wood also the resistance or the capacity of wood which can stand strong for a long time after being affected by several factors.
Mechanical Properties of Wood
The mechanical properties of wood can be explained as the capability of wood to withstand externally applied forces. These include different types of properties to understand the strength, resistivity, elasticity, durability, etc. many more characteristics of wood. The mechanical properties of wood were further classified into two. One is strength properties and the other is elasticity properties. There are different standards available to check the strength of wood. They are -
ISO (International standard institution
ISI (Indian standard Institution)
BSI (British Standard Institution)
PSI (Pakistan Standard Institution)
Compression - The compression of wood depends on the directions of applied forces, like -
perpendicular to wood grain
parallel to wood grain, and
an angle to the wood grain.
Tension - The tension is very effective on wood when it is parallel to the wood's grain.
Bending - Based on the load put on the wood, bending may occur. It shows the strength and stability of wood even if the load is increased in a parallel direction.
Conclusion
Wood is one of the most important materials used for several household and commercial purposes. Different types of physical properties and mechanical properties of wood explain the characteristics of a particular type of wood. All these properties were generalized to all types of wood. Few differences may occur accordingly.
FAQs on Properties of Wood Explained
1. What are the main categories of properties used to describe wood?
The properties of wood are generally classified into four main categories that explain its behaviour under different conditions. These are:
Physical Properties: Characteristics that can be observed or measured without changing the wood's chemical composition, such as colour, density, and lustre.
Mechanical Properties: The wood's ability to resist external forces, including its strength, elasticity, and hardness.
Thermal Properties: How wood responds to heat, primarily its conductivity and insulating capabilities.
Electrical Properties: The ability of wood to conduct or resist the flow of electricity, which is highly dependent on its moisture content.
2. What are the key physical properties of wood?
The primary physical properties of wood help in its identification and selection for various applications. Key examples include:
Colour and Appearance: The natural colour and grain pattern are crucial for aesthetic uses like furniture and flooring.
Density: Defined as mass per unit volume, density affects the wood's strength and weight. Woods like balsa are low-density, while oak is high-density.
Lustre: This refers to the way wood naturally reflects light, giving it a characteristic shine or dullness.
Odour: Certain woods, like sandalwood and cedar, have a distinct and often pleasant smell due to volatile organic compounds.
3. Can you explain the main mechanical properties of wood?
Mechanical properties determine how wood performs under stress and load, which is critical for construction and structural uses. The main properties are:
Strength: This includes compressive strength (resisting crushing forces), tensile strength (resisting pulling forces), and bending strength. Wood is particularly strong in tension when the force is applied parallel to the grain.
Elasticity: The ability of wood to bend under a load and return to its original shape after the load is removed.
Hardness: This is the wood's resistance to dents, scratches, and wear. It is a vital property for flooring and work surfaces.
4. How do thermal and electrical properties explain wood's use as an insulator?
Wood is an excellent thermal and electrical insulator due to its internal structure. Its porous nature, with tiny air pockets within its cellular structure, significantly slows down the transfer of heat. This is why it feels warm to the touch and is used for handles on cookware. Similarly, dry wood has very few free electrons to carry an electric current, making it a poor conductor of electricity and a safe material for use in buildings and around electrical applications.
5. What factors influence the strength and durability of wood?
Several factors can significantly affect the inherent strength and long-term durability of a piece of wood. The most important ones are:
Moisture Content: This is a critical factor. As the moisture content in wood increases, its strength decreases. Properly dried or 'seasoned' wood is much stronger.
Density: Generally, woods with a higher density are stronger and more durable than those with lower density.
Grain Direction: The orientation of wood fibres (the grain) determines its strength. Wood is strongest when forces are applied parallel to the grain.
Defects: The presence of knots, cracks, or insect damage can create weak points and significantly reduce the overall strength of the wood.
6. How does the grain of the wood affect its mechanical strength?
The direction of the grain is crucial because wood is an anisotropic material, meaning its properties are direction-dependent. It is significantly stronger when a force is applied parallel to the grain (along the length of the fibres) compared to when the force is applied perpendicular to the grain (across the fibres). This is why wooden beams are always cut so that the load is supported along the grain, maximising their tensile and bending strength.
7. Why is wood used for making furniture but not for cooking pots?
This is a perfect example of how different properties determine application. Wood is used for furniture because of its desirable mechanical properties (strength, workability) and physical properties (aesthetic colour and grain). However, it is not used for cooking pots due to its thermal properties. Wood is a poor conductor of heat (an insulator) and is also combustible. A cooking pot needs to efficiently conduct heat to the food, a property that metals excel at. Wood would burn and fail to heat the contents effectively.
8. If wood is a poor conductor, under what conditions can it conduct electricity?
While completely dry wood is an excellent electrical insulator, its conductivity increases dramatically with its moisture content. Water itself, especially if it contains dissolved minerals and impurities, can conduct electricity. When wood absorbs water, the water fills its pores and fibrous structure. This moisture provides a path for electric current to flow, turning the wood from a reliable insulator into a potential conductor. This is why it is dangerous to handle electrical equipment with wet hands or near wet wooden structures.
