A thread might need to be left-handed to prevent operational stresses from loosening it. Sometimes the opposite (left-handed, counterclockwise, reverse) sense of threading is used for a special reason. The reason for the clockwise standard for most screws and bolts is that supination of the arm, which is used by a right-handed person to tighten a screw clockwise, is generally stronger than pronation used to loosen. Almost all threaded objects obey this rule except for a few left-handed exceptions described below. To apply the right-hand rule, place one's loosely clenched right hand above the object with the thumb pointing in the direction one wants the screw, nut, bolt, or cap ultimately to move, and the curl of the fingers, from the palm to the tips, will indicate in which way one needs to turn the screw, nut, bolt or cap to achieve the desired result. Typical nuts, screws, bolts, bottle caps, and jar lids are tightened (moved away from the observer) clockwise and loosened (moved towards the observer) counterclockwise in accordance with the right-hand rule.Ĭonventional direction of the axis of a rotating body In 2014 under Bolivian president Evo Morales, the clock outside the Legislative Assembly in Plaza Murillo, La Paz, was shifted to counterclockwise motion to promote indigenous values. One historic Jewish clock was built that way in the Jewish Town Hall in Prague in the 18th century, using right-to-left reading in the Hebrew language. Occasionally, clocks whose hands revolve counterclockwise are sold as a novelty. The best-known surviving example is the Münster astronomical clock, whose hands move counterclockwise. Some clocks were constructed to mimic this. This effect is caused by the plane of the dial having been rotated through the plane of the motion of the sun and thus the shadow is observed from the other side of the dial's plane and is observed as moving in the opposite direction. For a vertical sundial (such as those placed on the walls of buildings, the dial being below the post), the movement of the sun is from right to top to left, and, accordingly, the shadow moves from left to down to right, i.e., counterclockwise. ![]() This is why hours must be drawn in horizontal sundials in that manner, and why modern clocks have their numbers set in the same way, and their hands moving accordingly. Then, when the Sun moves in the sky (from east to south to west), the shadow, which is cast on the sundial in the opposite direction, moves with the same sense of rotation (from west to north to east). In order for such a sundial to work north of the equator during spring and summer, and north of the Tropic of Cancer the whole year, the noon-mark of the dial must be placed northward of the pole casting the shadow. Clocks with hands were first built in the Northern Hemisphere (see Clock), and they were made to work like horizontal sundials. Scientifically riveting and practically empowering, Counterclockwise holds enormously exciting implications for our general health-including vision, old age, cancer, weight, and heart health-as well as for our fundamental happiness.The shadow of a horizontal sundial in the Northern Hemisphere rotates clockwiseĬlocks traditionally follow this sense of rotation because of the clock's predecessor: the sundial. Langer describes ways to reorient our attitudes and language in order to achieve better health she shows us the ways in which our belief in physical limits constrains us and she demonstrates how our desire for certainty in medical diagnosis and treatment often prevents us from fully exploiting the power of uncertainty. If we could turn back the clock psychologically, could we also turn it back physically? For more than thirty years, award-winning social psychologist Ellen Langer has studied this provocative question, and now has a conclusive answer: opening our minds to what’s possible, instead of clinging to accepted notions about what’s not, can lead to better health at any age.ĭrawing on her own body of colorful experiments-including the first detailed discussion of her landmark 1979 “counterclockwise” study in which elderly men lived for a week as though it was 1959 and seemed to grow younger-and important works by other researchers, Langer proves that the magic lies in being aware of the ways we mindlessly react to cultural cues.Ĭounterclockwise shows how we can actively challenge these ingrained behaviors by making subtle changes in our everyday lives. ![]() – Dan Ariely, Ph.D., author of Predictably Irrational. She is a fantastic storyteller, and Counterclockwise is a fascinating story about the unexpected ways in which our minds and bodies are connected. Notes:Take a brilliant, creative social scientist, without any respect for conventional wisdom and you get Ellen Langer.
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