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My presentation on the material wood.

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MY PRESENTATION ON THE MATERIAL WOOD What is Wood? Wood is an organic substance composed of cells. It forms through cell division in the formative tissue (cambium) located between the bark and the wood. Under the climatic conditions existing in Switzerland, wood formation follows a seasonal rhythm; forming in the growing period from spring to autumn and halting in winter. In the process, tree rings develop which are visible in the transversal and longitudinal sections of the stem. Construction of a tree stem Wood - a renewable raw material * Wood is one of Switzerland's only raw materials. * Wood grows on continually and is available in times of crisis. * The supply of wood is decentralized: wood is usually used from nearby forests. * In comparison with other materials, wood takes little energy to process. Wood - a raw material * Wood can be used in handicrafts and industry. * Waste wood can be processed and used again. * Wood is solid but relatively light which makes it easy to transport and handle. * Wood is a good insulator. It protects against temperature extremes. Wooden walls, ceilings and floors have a surface temperature just below room temperature. * Wood exhibits good acoustic properties. It vibrates within hearing range and can reflect or absorb sound waves. A tree stem consists of three areas; pith, xylem and bark. The central pith (F) is usually barely visible and does not increase in size through the life of the tree. ...read more.


These glucose anhydride units then polymerise into long chain cellulose molecules that contain from 5,000-10,000 glucose units. Because of the nature of the bonds between adjacent glucose anhydride units, the basic repeating unit of the cellulose polymer consists of two glucose anhydride units, and is called a cellobiose unit. FORMATION OF SOFTWOOD AND HARDWOOD ATOMIC SYMBOLIC Durability Wood is naturally a very durable substance. If not attacked by living organisms, it will last for hundreds or even thousands of years. Samples of wood used by the ancient Romans have been found virtually in their original condition when a combination of circumstances protected them against attack. The most important of the organisms attacking wood are the fungi that cause so-called dry rot, which actually occurs only when the wood is damp. The sapwood of all trees is susceptible to this type of decay, but the heartwood of a few species is naturally resistant to these fungi. Walnut, redwood, cedar, mahogany, and teak are among the well-known woods that are extremely durable. Other woods are resistant to various types of attack. Greenheart and teak are particularly resistant to the attack of marine borers, and so are often used for underwater construction for wharves. A number of woods are comparatively resistant to termites, including redwood, black walnut, mahogany, and several types of cedar In most of these cases, the woods are aromatic, and the resistance is probably due to the resins and similar chemicals they contain. Wood may be preserved by protecting it chemically against deterioration. ...read more.


The air pockets make sure there is not heat transfer. Physical Properties The principal physical properties of wood are strength, hardness, stiffness, and density. Density is generally an indication of the mechanical properties, inasmuch as dense woods are usually hard and strong. The term strength covers a number of essentially different properties; a wood that is high in one kind of strength is not necessarily high in others. Moreover, the strength varies greatly with the state of seasoning, or dryness, of the wood, and with the direction of the grain; wood is always much stronger when cut along the grain rather than across it, and for this reason planks and such articles as poles and handles are always cut with the grain running the long way. Wood has high compression strength, in some cases higher in proportion to its weight than steel; it has low tensile strength and moderate shear strength. High compression strength is required for foundations, and for the main supports of buildings. Bending strength is essential for most structural wooden members, including joists, studding, and beams of all sorts. Many woods that are commonly used for high bending strength have high compression strength, and vice versa; but oak, for example, is very strong in bending and comparatively weak in compression, whereas redwood is strong in compression and comparatively weak in bending. Toughness is a measure of strength against sudden and repeated stress. Hickory and ash are outstanding for their toughness and are used in wagon spokes, baseball bats, and axe handles; because hickory is stiffer than ash, it is preferred for thin handles, such as those of golf clubs. ...read more.

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