The producers of instant coffee found their product strongly resisted in the market places in spite of their products’ manifest advantages. However, the advertising expenditure for instant coffee was far greater than which for regular coffee. Efforts were made to find the cause of the consumers’ seemingly reasonable resistance to the product. The reason given by most people were dislike of the taste. The producers suspected that there might be deeper reasons, however. This confirmed by one of motivation research’s classic studies, one often cited in the trade. Mason Haire of the University of California, constructed two shopping lists that were identical except from one item. There were six items common to both lists with the brands or amounts specify. The seventh item, in fifth place on both lists, read Maxwell House coffee on one list and Nestle Instant Coffee on other. One list was given to each one in a group of fifty women, and the other list to those in another group of the same size. The women were asked to study their lists and then to deseribe, as far they could, the kind of women (personality and character) who would draw up that shopping list. Nearly half of those who had received the list including instant coffee was described a house-wife who was lazy and a poor planner. On the other hand, only one woman in the other group described the housewife, who had included regular coffee on her list, as lazy. ______
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砷盐检查需要的试药 吸收硫化氢气体
A. 醋酸铅棉花
B. 溴化汞试纸
C. 金属锌与盐酸
D. 碘化钾和酸性氯化亚锡试液
目前,影响PC机运行安全的最大威胁是【16】,它县有破坏性、隐蔽性、传染性和潜伏性等特点。
关于妊娠合并心脏病对胎儿的影响,哪项是正确的
A. 妊娠合并心脏病的孕妇和其胎儿的预后均很差
B. 二尖瓣狭窄手术后,心功能Ⅰ级的孕妇,易发生早产
C. 心功能Ⅲ级以上的孕妇,胎儿窘迫的发生率高
D. 心脏代偿功能良好,也易引起死胎
E. 单纯房间隔缺损的孕妇,易发生胎儿宫内生长迟缓
If a mother pushes her small son in a swing, giving only a light force each time he returns, eventually he will be swinging quite high. The child can do this for himself by using his legs to increase the motion, but both the mother’s push and the child’s leg movements must occur at the proper moment, or the extent of the swing will not increase. In physics, increasing the swing is increasing the amplitude; the length of the rope on the swing determines its natural oscillation period. This ability of an object to move periodically or to vibrate when stimulated by a force operating in its natural period is called resonance. Resonance is observed many times without consciously thinking about it; for example, one may find an annoying vibration or shimmy in an automobile, caused by a loose engine mount vibrating with increasing amplitude because of an out-of-round tire. The bulge on the tire slaps the pavement with each revolution; at the natural resonance point of the engine mount, it will begin to vibrate. Such vibrations can result in considerable damage if allowed to persist. Another destructive example of resonance is the shattering of a crystal goblet by the production of a musical tone at the natural resonant point of the goblet. The energy of the sound waves causes vibration in the glass; as its amplitude increases, the motion in the glass exceeds the elasticity of the goblet, and it shatters. An instrument called a tachometer makes use of the principle of resonance. It consists of many tiny bars, loosely fastened together and arranged so that each bar can slide independently of the others. Movement of the bars causes changes in a dial. When placed next to a rotating motor or engine, the tachometer picks up slight vibrations which are transferred to the resonant bars. These bars begin to move, and the resulting dial may be read to find the revolutions per minute of the motor very quickly. In which of the following cases is it useful to consider the relationship between the length of an oscillating object and its natural period
Adjusting the speed of a car.
B. Adjusting a clock pendulum.
C. Adjusting tire balance.
D. Adjusting engine mounts.