3.6 The signed area under a constant velocity-time graph There is a simple feature of uniform velocity-time graphs that will be particularly useful to know about when we come to consider non-uniform motion in the next section. It concerns the relationship between the velocity-time graph and the change in position over a given time interval. Consider the following problem. A vehicle travels at a velocity vx = 12 m s−1 for 4 s. By how much does its position change over that interval? The answer, from Equati
2.3 Position-time graphs Tables do not give a very striking impression of how one thing varies with respect to another. A visual form of presentation, such as a graph, is usually much more effective. This is evident from Figure 7, which shows the graph obtained by plotting the data in Table 2 and then drawing a smooth curve through the resulting points. 1 From drop-towers to Oblivion - some applications of linear motion We have all experienced that momentary feeling of lightness when an elevator begins its downward motion. It is almost as if our weight had suddenly been reduced or, conceivably, that the pull of the Earth's gravity had decreased for a moment. But imagine what it would be like if the lift cable had suddenly snapped and the lift, with you in it, had plummeted downward. Apart from stark terror, what else do you think you would experience during your fall? What would the physical experience 2 The Ordovician seas Before going any further, click on 'View document' below and read pages 68-71 from Douglas Palmer's Atlas of the Prehistoric World. Collecting seashells on an Ordovician beach would have been a rather curious experience. Whilst most shells were made of similar materials to those found on a modern beach, the detailed form of many would have Acknowledgements The material acknowledged below is Proprietary and used under licence, not subject to Creative Commons. See Terms and Conditions. Grateful acknowledgement is made to the following sources for permission to reproduce material in this course: Course image: MattysFlicks in Flickr made available under Author(s): 4.4 Obesity and cardiovascular diseases Obesity and being overweight are well-known as risk factors for cardiovascular diseases. Carrying excess body fat predisposes individuals to developing elevated blood cholesterol and diabetes. You will begin to appreciate that many of the modifiable risk factors for cardiovascular diseases are interlink 1.3.1 Who is affected by cardiovascular diseases? Cardiovascular diseases are the main cause of premature death (before the age of 75) in the UK, across Europe and the USA – indeed, across many parts of the world (Figures 3 and Author(s): 2.5 Expressing probability According to Equation 1, probability is defined as a fraction. However a fraction such as 1.3 Scales of measurement In thinking about the sizes of things, it is sometimes useful to do so in quite rough terms, just to the nearest power of ten. For example, 200 is nearer to 100 than it is to 1000, but 850 is nearer to 1000 than it is to 100. So if we were approximating to the nearest power of ten we could say 200 was roughly 102, but 850 was roughly 103. This process is called reducing the numbers to the nearest order of magnitude. Acknowledgements This extract is taken from S809 © 2005 The Open University. Course image: Liz West in Flickr made available under Creative Commons Attribution 2.0 Licence. All written material contained within this course originated at the Open University. Don't miss out: 7 Conclusion Perhaps you are asking yourself why there are so many different imaging modalities. Is there not one that will do everything that is required? The answer, at the moment, is ‘No’. With most of the imaging te 6.3.3 Photomultiplier tubes and detection circuitry The visible photons are collected by an array of photomultiplier tubes behind the crystal. These convert each visible photon to an electron and then multiply the number of electrons sufficiently to give a voltage pulse. Because the number of visible photons is proportional to the energy of the incoming gamma ray, the height of the pulse depends on this energy. This gives a method of counting the numbers of gamma photons at different energies that reach the crystal. A resistive network c 2.2.1 X-ray source X-rays are produced when energetic electrons strike a metal target. The X-ray source consists of an evacuated tube containing a cathode, from which the electrons are emitted, and an anode, which supports the target material where the X-rays are produced. Only about 1 per cent of the energy used is emitted as X-rays – the remainder is dissipated as heat in the anode. In most systems the anode is rotated so that the electrons strike only a small portion at any one time and the rest of the ano 2.6 How can we find out more about Europa? There are currently no scheduled missions to Jupiter's moons, since NASA's Jupiter Icy Moons Orbiter (JIMO) was cancelled in 2005, but Europa remains a high priority target for both NASA and ESA, so a mission with simlar objectives to JIMO seems likely by about 2020. On arrival at Jupiter, JIMO would have gone into orbit first round Callisto, then Ganymede and finally Europa. The main objectives of JIMO at Europa would have been to: Determine the 1.5 The Galileo mission It was a long time before the Voyager missions were followed up by more detailed surveys of the outer planet satellites. No Uranus or Neptune missions are planned, but a mission to Saturn called Cassini-Huygens was launched in 1997 for arrival at Saturn in 2004. However, the Jupiter system received a similar visitor first. This was Galileo, launched in 1989, which became the first spacecraft to orbit Jupiter in December 1995. It continued to function through 2002, and was destroyed by plungin 3.5.2 Vocal communication In order to be able to state that animals are communicating vocally with one another, scientists need to demonstrate that particular sounds made by one individual can be understood and acted upon by others. 3 Somatic gene therapy There is a distinction between somatic cells, those making up almost all of the body, and germline cells, which are the eggs and sperm and the cells that produce them. Somatic gene therapy is the transfer of genes into the somatic cells of the patient, such as cells of the bone marrow, and hence the new DNA does not enter the eggs or sperm. The genes transferred are usually normal alleles that could ‘correct’ the mutant or disease alleles of the recipient (see Study Note 2: The 7 Conclusions Throughout this course, numerous examples of science promotion have been given, from the individual level of Pro-Ams to the supranational level of the EU Action Plan. Is there an appropriate political level for initiating science promotion or might a multi-level approach be more fruitful? Certainly there is evidence that local or sub-national initiatives can engage people – from Science Cafés and Cities of Science, to the Pub Understanding of Science beer mats with scientific questio Learning outcomes After studying this course, you should be able to: demonstrate an awareness of the issues surrounding public understanding of science engage with some of the debates surrounding this topic. 1.2 Artificial selection Selection acts on phenotypic characters whatever their origin, and can retain or eliminate the characters' genetic basis. Artificial selection is any selective breeding intentionally practiced by humans leading to the evolution of domesticated organisms. Artificial selection may oppose or amplify or be neutral in relation to natural selection. Most livestock, including dogs, cats, goats, pigs, cattle, sheep, guinea pigs, horses, geese and poultry and scores of crop plants were d
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Activity 17
Activity 5
