3 Needs and problems The last section has established that engineering is about satisfying needs. In fact, with so many needs, it's a wonder that not everyone is an engineer! So, now that we have talked about both needs and problems, the logical progression is to examine the relationship between them. Take the water example as being a fundamental need. We can state it thus: This village needs a supply of clean water. 5.13.2 Circular membrane When a membrane that is stretched over a circular frame is struck, energy is supplied, which again causes the membrane to vibrate in a number of modes simultaneously. The first six modes in which the circular membrane can vibrate are shown in Figure 20. The diagrams comprise circles that are conce 5.5 Vibrating string: pitches of notes produced by stringed instruments When a string is bowed, plucked or struck, energy is supplied that starts the string vibrating. The string doesn't just vibrate in one single mode; instead, it vibrates in a combination of several modes simultaneously. The displacement along the string is the superposition of the standing-wave patterns corresponding to those modes. For example, if the string vibrated only in the first and second modes, the displacement at a given instant of time might appear as shown in Author(s): 5.3 Vibrating string: standing waves on a string We still haven't answered the question of how standing waves are set up on a string. To do so we need to return to our string, fixed at one end and held in someone's hand at the other end. Imagine now that instead of sending a single pulse along the string, the person flicks their hand up and down periodically and sends a sinusoidal wave along the string. This wave gets reflected and inverted at the fixed end and travels back towards the person holding the string. There are now two waves of t 4.7 Summary Water in its 'natural' state supports a complex, yet fragile, ecosystem. The ability of natural watercourses to sustain aquatic life depends on a variety of physical, chemical and biological conditions. Biodegradable compounds, nutrients and dissolved oxygen must be available for the metabolic activities of the algae, fungi, bacteria and protozoa which are at the lowest level of the food chain. In addition, plant and animal growth cannot occur outside narrow ranges of temperature and pH. Susp 4.6 Tidal rivers and estuaries Most of the major cities and harbours in the world are located on estuaries. The estuarine ecosystem is a unique intermediate between the sea, the land and fresh water. A rather precise definition of an estuary is 'a semi-enclosed coastal body of water, which has a free connection with the open sea, and within which sea water is measurably diluted with fresh water derived from land drainage'. This excludes large bays with little or no freshwater flow, and large brackish seas and inland 3.5.5 Biological indicators A great many biological species and individuals occur in normal streams. These often differ markedly in their sensitivity to environmental factors, and likewise the tolerances of various species to different types of pollution vary considerably. The major groups of organisms that have been used as indicators of environmental pollution include bacteria, fungi, protozoa, algae, higher plants, macroinvertebrates and fish. The benthic 'bottom living' macroinvertebrates are particularly suitable a 2.7 Infiltration Entry of precipitation through the soil surface and on downwards, by gravity, is known as infiltration. The rate at which this process can take place is governed by the permeability (a measure of the ease with which water can flow through the subsurface layer) and by the existing degree of saturation of the soil. Infiltration can be impeded by outcropping impermeable rocks or by paved areas, and also by the presence of finegrained soils with a low permeability (such as clay). At certain times 3.1 The acquisitive model of learning The three models are introduced in turn, and each is followed by an activity that invites you to apply the model to your studies. This model of learning starts from a focus on the observable behaviour of the learner and on the idea that this can be changed by feedback from the learning environment. It is associated with the idea that learning has to do with reproducing some desirable behaviours or measurable outcomes. The learning process is seen as a process of accretion. Learner 3.4.5 Fretting fatigue An additional possibility was considered. It was known that there was significant movement of the bridge during passage of traffic, because users had noticed it many times when crossing. The joints would thus have been subjected to rotary motion around the pin in order to accommodate such vibrations. Could these have caused fatigue crack growth at the bearing surfaces? Contact between a circular and a flat plate creates so-called Hertzian stresses at the contact zone: compressive at the 3.4.1 Fracture surface One half of the eye at the joint is shown in Figure 38(a), and it shows two breaks in the limbs either side of the pin-hole. Although both appear brittle in this picture, in fact one side showed signs of ductile deformation. The way it had fractured was unique when compared with the other eye 3.3.4 Examining the parts Brittle fractures were discovered quickly in the mass of debris hauled from the river. Such samples became the focus of increasing effort as time went by, simply because they were unexpected. So the possible failure mechanisms were immediately narrowed down when brittle fractures of critical components started to emerge from the river. 1.3 Environmental factors I indicated earlier that many failures occur after a product has been in service for some time: such as the wear of a car tyre, or corrosion of the car body itself. It is also possible for components to fail because of a combination of a manufacturing defect with the applied loading or with the environmental conditions during use. Author(s): David Hume: 18th Century Philosopher Art history: modern and contemporary Art history: early modern John Webster, The Duchess of Malfi An introduction to material culture Introduction This unit focuses on the creation of a semiconductor transistor – a versatile tiny transistor that is now at the heart of the electronics industry. In the video clips, the history of the incredible shrinking chip, its Scottish connections and an explanation of the physics that make chips work are accompanied by a reconstruction of making a transistor using the crude techniques of yesteryear. This OpenLearn course provides a sample of Level 2 study in Author(s): Introduction This course investigates certain philosophical questions concerning the nature of emotions. This OpenLearn course provides a sample of Level 3 study in Arts and Humanities.
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2011 is the 300th anniversary of the birth of one of the greatest figures in Western Philosophy – David Hume. As well as an economist and historian, Hume was specifically known for his scepticism and empiricism, and was also an important figure in the Scottish Enlightenment period in the 18th century. In this audio collection, The Open University’s Nigel Warburton is joined by A.C. Grayling and other philosophers to discuss Hume’s key theories around the self, induction and his argument a
Baffled by modern art and architecture? You’re not alone! This collection gives new insight into today’s shifting kaleidoscope of visual culture by placing it in the context of the developments of the 19th and 20th century. In the mid 19th century there was a growing realisation that everything had changed. Industry was booming, and the speed of life increasing. Artists, thinkers and architects strove to find new ways of encapsulating this new world … and modernism was born. The coll
The world of the early modern period (C10th - C16th) was one of religious obsession, power struggles and plunder. But it was also a world of stunning artistic endeavour. This collection shows how, encoded in the art and architecture of the time, you can find stories of political machinations, female influence and surging movements of people. We may think our own era has a monopoly on long-distance travel, but in the mediaeval period it was perfectly possible for Western Catholic artists to enc
This free course, John Webster, The Duchess of Malfi, concentrates on Acts 1 and 2 of John Webster's Renaissance tragedy, The Duchess of Malfi. It focuses on the representation of marriage for love and the social conflicts to which it gives rise. The course is designed to hone your skills of textual analysis.
First pu
This free course, An introduction to material culture, introduces the study of material culture. It asks why we should study things and outlines some basic approaches to studying objects. Dr Rodney Harrison.
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