5.3 Summary The term phase is used to refer to the part of a cycle that an oscillating system is in at a particular moment. For two sine waves of the same frequency that are not in step, one wave lags or leads the other in time. We can express the amount by which they are out of step as a phase difference. Usually phase difference is expressed as a fraction of a cycle or as a certain number of degrees (one complete cycle corresponding to 360°). If two (or more) sine waves are completely out of pha
4.1 The experimental result One way to establish the speed of sound is to measure it experimentally. That is, one measures how long the sound takes to travel a known distance, and from this works out the speed. The answer turns out to depend somewhat on the prevailing temperature and humidity. At an air temperature of 14 °C the speed is 340 metres per second and at about 22.5 °C it is 345 metres per second. That is a change of speed of less than 1.5 per cent for an appreciable change of temperature. To a reasonable ap
2.1 The importance of sine waves For much of the rest of this unit we shall be concerned with the properties of a type of sound wave that when represented as a graph has a characteristic shape known as a sine wave. Figure 1 shows you what a sine-wave graph looks like. For the moment you need not be concerned with what this grap
5.8 Developing a soft systems method One of the more widely used systems methods is known by its originators as ‘soft systems methodology’ or SSM. The driving force behind its development and increasing application in the domain of information systems development has been Peter Checkland at the University of Lancaster in the UK (e.g. see Checkland and Holwell, 1997). SSM, or adaptations of it, has been used in many other domains as well. The experiences that have given rise to the development of what in this course I
3.5 Distinctions about systems practice A tension has existed throughout the history of Western thought around whether to focus on parts or the whole. The practice that springs from this history carries the same tension. This tension has been particularly visible within science and philosophy for a long time and it gives rise to different approaches. I will be addressing these tensions in Author(s):
10.4 Desire to make money While most inventors might dream of growing rich from their inventions few invent for that reason alone. There are some exceptions though. Take the case of the safety razor. One person, a travelling salesman named King Camp Gillette, was primarily responsible for the original invention and prototype. Unlike many lone inventors Gillette was not inventing something arising from a hobby or a field of technology with which he was already familiar. He was deliberately searching for a winner.
2 New products – old failings This section introduces product ‘usability’. It offers a case study of a vegetable peeler to illustrate how usability issues exist alongside other important concerns in the product development process. If you look around high-street or shopping-mall stores, you cannot help but notice the number and variety of new products on offer. This year's washing machine or dishwasher, stylish furniture, multi-feature telephones, audio systems, DVD players, digital cameras and camcorders, all b
5.11 Plumbo-solvency Many
water supplies
in the UK are naturally acidic, and when this type of water is supplied through lead pipes the lead dissolves into the water. Lead pipes are dominant in many older established areas. The Drinking Water Directive has set a maximum admissible concentration of 10 μg 1−1 lead in water, to be achieved by the year 2013. The obvious solution to this problem is to remove all lead piping but this is a costly exercise. As an interim measure, the water l
3.4 Chemical characteristics of natural waters Since water is such a good solvent, it is not surprising to find many different chemical substances present in it. Water, on reaching a river, will contain inorganic and organic compounds which were dissolved as rainwater percolated through the soil and rocks. In addition, some gases will dissolve in rainwater during its passage through the air. The substances present in water may be conveniently grouped into: those from dissolved gases such as
2.11 Storage In a given fixed space at any phase of the hydrological cycle, there is an inflow and an outflow of water, the rates of which vary with time. The total cumulative difference between inflow and outflow is the storage. So within that space there is a body of water whose mass is not directly controlled by instantaneous values of inflow and outflow. For example, in river flow the movement of the whole body of water in the channel is generally downstream, yet a given reach contains a volume whose
1 Some facts about water