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Strength of material 2 - Essay Example Beams: Beams are often classified according to their ideal support conditions as either simply supported beams or cantilever beams. Beams are subject to bending stresses when loads are applied and experience compressive, shear and tensile forces. A simply supported beam is fixed on two ends. When loading the maximum tensile stress occurs at the midpoint of the bottom edge of the beam and the maximum compressive stress occurs at the midpoint of the top edge. A cantilever beam is supported on one end only and must be built into the wall that supports it. Two forces act on cantilever beams â€“ firstly, a vertical upward force which supports the weight of the beam and any downward loads and secondly â€˜the fixing momentâ€™ which prevents the unsupported beam from falling (Eric William Nelson et all, 1997). A beam may be strong enough to resist bending moments set up by its load and yet may sag without collapsing. This is called deflection and is dictated by the elasticity and strength of the material used to build it. Columns and Struts: Columns, also known as stanchions support compressional loads along their longitudinal axes. The effective of excessive loading on a column is that the column could cause it buckle or crush like a wall coming down. A â€˜short columnâ€™ is one whose height is small relative to its thickness is small relative to its thickness. Whether or not the column will remain stable under increasing axial load will depend on the strength of the material that constitutes the column. A â€˜longâ€™ or â€˜slenderâ€™ column has a greater height relative to its thickness. A long column becomes unstable and buckles at a load much smaller than which would crush a short column of the same cross-section and material. This is called the â€˜critical loadâ€™. Unlike beams, the loading capacity of a column depends less upon the strength of the material of which it is made than upon its stiffness and this decreases with a
Today we will discuss the ethics of conserving depletable resources. Points to be covered in this lesson: â€¢ It might appear that we have an obligation to conserve resources for future generations because they have an equal right to the limited resources of this planet. â€¢ â€¢ Conservation of resources Economic growth vs conservation â€¢ â€¢ â€¢ Future generations have an equal right to the planetâ€™s limited resources By depleting these resources we are depriving them of what is rightfully theirs So we ought to do our utmost to practice conservation â€¢ To minimize depletion To avoid violating the rights of future generations However, some of the writers claimed that it is a mistake to think that future generations have rights and there are three main reasons for that: 1. Future generation do not exist right now and may never exist. Since there is a possibility that future generation may never exist, they cannot â€œpossessâ€ rights. 2. If future generations did have rights, then we might be led to the absurd conclusion that we must sacrifice our entire civilization for their sake. 3. We can only say that someone has a certain right only if we know that he or she has a certain interest, which that right protects. The purpose of a right, after all, is to protect the interests of the right-holder, but we are virtually ignorant of what interests future generation will have. Justice to Future Generations â€¢ John Rawls that while it is unjust to impose disproportionately heavy burdens on present generations for the sake of future generations, it is also unjust for present generations to leave nothing for future generations. What do you mean by the word Conservation? Utilitarian Analysis also favors this theory: Each generation has a duty to maximize the future beneficial consequences of its actions and to minimize their future injurious consequences for succeeding generations, as well as themselves. However, utilitarians have claimed, these future consequences should be â€œdiscountedâ€ in proportion to their uncertainty and to their distance in the future. Unfortunately, we cannot rely on market mechanisms to ensure that scarce resources are conserved for future generations. The market registers only the effective demands of present participants and the actual supplies presently being made available. William Shepherd and Clair Wilcox explained six reasons for the heavy discounting or â€œlive for todayâ€ character of markets endangered species; that we should take steps to ensure that the rate of consumption of fossil fuels and of minerals does not continue to rise; that we should cut down our consumption and production of those goods that depend on nonrenewable resources; that we should recycle nonrenewable resources; that we should search for substitutes for materials that we are too rapidly depleting. Economic Growth? However, to many observers conservation measures fall far short of what is needed. Several writers have argued that if we are to preserve enough scarce resources so that future genera- tions can maintain their quality of life at a satisfactory level, we shall have to change our economies substantially, particu-larly by scaling down our pursuit of economic growth Others argue that economic systems will have to abandon their goal of steadily increasing pro-duction, and put in its place the goal of decreasing production until it has been scaled down to â€œa steady stateâ€- that is, a point at which â€œthe total popula-tion and the total stock of physical wealth are maintained constant at some desired levels by a â€˜minimalâ€™ rate of maintenance throughout (that is, by birth and- death rates that are equal at the lowest feasible level, and by physical pro-duction and consumption rates that are equal at the lowest feasible level). â€The conclusion that economic growth must be abandoned if society is to be able to deal with the problems of diminishing resources has been chal-lenged. It is at least arguable that adherence to continual economic â€˜growth promises to degrade the quality of life of future generations. The arguments for this claim are simple, stark, and highly controversial. If the worldâ€™s economies continue to pursue the goal of economic growth the demand for depletable resources will continue to rise. But since world resources are finite, at some point supplies will simply run out. We can expect a collapse of the major economic institutions (that is, of manufacturing and financial institutions, communication networks, the service industries) which in turn will bring down the political and social institutions (that is, centralized govern- ments, education and cultural programs, scientific and technological development, health care). Living standards will then decline precipitously in the wake of widespread star-vation and political dislocations. Various scenarios for this sequence of events have been constructed, all of them more or less specula- tive and necessarily based on uncertain assumptions. Multiple access: If a resource can be used by several different extractors, then the shared access will inevitably lead the resource to be depleted too fast â€¢ For example: several people with straws in the same milkshake, it will be in the private interest of each to suck faster to get the most for themselves Time preferences and myopia: Firms generally have short time horizons â€¢ â€¢ Under the stresses of competition Apt to give insufficient weight to the demands of future generations Inadequate forecasting: Present users may simply fail to foresee future â€¢ Consequences for example: DDT spraying in the 50s no one foresaw that it would build up in the environment with harmful effects Short run tax breaks and other incentives Encourage overly rapid use of resources Resource depletion like pollution, an external cost, not borne directly by the firm . So itâ€™s in the economic self interest of the firm to ignore this cost Special influences: â€¢ â€¢ â€¢ External effects: Distribution: private market decisions are based on existing patterns of wealth and income distribution â€¢ â€¢ Resource users, in effect, vote with their dollars about what to produce in what amounts so the richer the individual the more say they have in what the market produces Future generations â€” having as yet no wealth or income â€” have as yet no â€œvoteâ€ â€¢ Doomsday Scenario â€¢ If the present situation continues â€¢ Explosive population growth will happen because of The only means of conserving for the future, then, appears to be voluntary policies of conservation. Rawlâ€™s view implies that while we should not sacrifice the cultural advances we have made, we should adopt voluntary or legal measures to conserve those resources and environmental benefits that we can reasonably assume our immediate posterity will need if they are to live lives with a variety of available choices comparable, at least, to ours. This means that we should preserve wild life and â€¢ â€¢ â€¢ â€¢ â€¢ Declining death rates Relatively stable birth rates Worldâ€™s economies continue to expand
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