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Wednesday, August 4, 2010

Wood


Wood is a solid material derived from woody plants, notably trees but also shrubs. Wood from the latter is only produced in small sizes, reducing the diversity of uses. In its most common meaning, "wood" is the secondary xylem of a woody plant, but this is an approximation only: in the wider sense, wood may refer to other materials and tissues with comparable properties. Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. Wood is composed of fibers of cellulose (40%–50%) and hemicelluloses (15%–25%) held together by lignin (15%–30%).

A tree increases in diameter by the formation, between the old wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. Where there are clear seasons, this can happen in a discrete pattern, leading to what is known as growth rings, as can be seen on the end of a log. If these seasons are annual these growth rings are annual rings. Where there is no seasonal difference growth rings are likely to be indistinct or absent.

Within a growth ring it may be possible to see two parts. The part nearest the center of the tree is more open textured and almost invariably lighter in color than that near the outer portion of the ring. The inner portion is formed early in the season, when growth is comparatively rapid; it is known as early wood or spring wood. The outer portion is the late wood or summer wood, being produced in the summer.

The types of wood are commonly classified as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from broad-leaved trees (e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than most hardwoods. Wood products such as plywood are typically classified as engineered wood and not considered raw wood.

Discussion of the uses of Wood

Wood has been used for millennia for many purposes. One of its primary uses is as fuel. It is also used as for making artworks, furniture, tools, and weapons, and as a construction material.Wood has been an important construction material since humans began building shelters, houses, boats. Nearly all boats were made out of rock till the late 1800s. It remains in common use today for some boats and houses.
In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction and exterior decoration. Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber will usually refer to felled trees, and the word for sawn planks ready for use will be timber.

Wood unsuitable for construction in its native form may be broken down mechanically (into fibres or chips) or chemically (into cellulose) and used as a raw material for other building materials such as chipboard, engineered wood, hardboard, medium-density fibreboard (MDF), oriented strand board (OSB). Such wood derivatives are widely used: wood fibres are an important component of most paper, and cellulose is used as a component of some synthetic materials. Wood derivatives can also be used for kinds of flooring, for example laminate flooring.

Wood is also used for cutlery, such as chopsticks, toothpicks, and other utensils, like the wooden spoon. There are also wood jug and many more creative creation which was made by wood.

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