15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 27)

One of the factors contributing to the intense nature of twenty-first-century stress is our continual exposure to media – particularly to an overabundance of news. If you feel stressed out by the news, you are far from alone. Yet somehow many of us seem unable to prevent ourselves from tuning in to an extreme degree.

         The further back we go in human history, the longer news took to travel from place to place, and the less news we had of distant people and lands altogether. The printing press obviously changed all that, as did every subsequent development in transportation and telecommunication.

         When television came along, it proliferated like a poplulation of rabbits. In 1950, there were 100,000 television sets in North American homes; one year later there were more then a million. Today, it’s not unusual for a home to have three or more television sets, each with cable access to perhaps over a hundred channels. News is the subject of many of those channels, and on several of them it runs 24 hours a day.

        What’s more, after the traumatic events of Sptember 11, 2001, live newcasts were paired with perennial text crawls across the bottom of the screen – so that viewers could stay abreast of every story all the time.

        Needless to say, the news that is reported to us is not good news, but rather disturbing images and sound bytes alluding to diasater (natural and man-made), upheaval, crime, scandal, war, and the like. Compounding the proplem is that when actual breaking news is scarce, most broadcasts fill in with waistline, hairline, or very existence in the future. This variety of story tends to treat with equal alarm a potentially lethal flu outbreak and the bogus claims of a wrinkle cream that overpromises smooth skin.

       Are humans meant to be able to process so much trauma – not to mention so much overblown anticipation of potetial trauma – at once? The human brain, remember, is programmed to slip into alarm mode when danger looms. Danger looms for someone, somewhere at every moment. Exposing ourslves to such input without respite and without perspective cannot be anything other than a source of chronic stress.

(Extracted from The Complete Idiot’s Guide to Beating Stress by Arlene Matthew Uhl – Penguin Group 2006)

The ability of falling cats to right themselves in midair and land on their feet has been a source of wonder for ages. Biologists long regarded it as an example of adaptation by natural selection, but for physicists it bordered on the miraculous.

Newton's laws of motion assume that the total amount of spin of a body cannot change unless an external torque speeds it up or slows it down. If a cat has no spin when it isreleased and experiences no external torque, it ought not to be able to twist around as it falls.

In the speed of its execution, the righting of a tumbling cat resembles a magician's trick. The gyrations of the cat in midair are too fast for the human eye to follow, so the process is obscured. Either the eye must be speeded up, or the cat's fall slowed down for the phenomenon to be observed. A century ago the former was accomplished by means of high-speed photography using equipment now available in any pharmacy. But in the nineteenth century the capture on film of a falling cat constituted a scientific experiment.

          The experiment was described in a paper presented to the Paris Academy in 1894. Two sequences of twenty photographs each, one from the side and one from behind, show a white cat in the act of righting itself. Grainy and quaint though they are, the photos show that the cat was dropped upside down, with no initial spin, and still landed on its feet. Careful analysis of the photos reveals the secret; as the cat rotates the front of its body clockwise, the rear and tail twist counterclockwise, so that the total spin remains zero, in perfect accord with Newton's laws. Halfway down, the cat pulls in its legs before reversing its twist and then extends them again, with the desired end result. The explanation was that while nobody can acquire spin without torque, a flexible one can readily change its orientation, or phase. Cats know this instinctively, but scientists could not be sure how it happened until they increased the speed of their perceptions a thousandfold.