题干

有两只外形完全相同且表面涂有相同颜色的实心铁球和铝球,请至少写出一种方法,将它们区分出来.

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答案(点此获取答案解析)

解:(1)用天平分别测出两个球的测质量,质量大的为铁球.

(2)调节好天平,把两个球分别放在天平的两盘,下沉的一端放的是铁球.

(3)用磁铁吸,能被磁铁吸引的是铁球.

故答案为:用天平分别测出两个球的测质量,质量大的为铁球.(答案不唯一)

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    Here is an astonishing and signficant fact:Mental work alone can't make us tired. It sounds absurd. But a few years ago, scientists tried to find out how long the human could labor without reaching a stage of fatigue(疲劳). To the amazement of these scientists, they discovered thett blood passing through the brain, when it is active, shows no fatigue at all! If we took a drop of blood from a day labourer, we could find it full of fatigue toxins(毒素) and fatigue products. But if we took blood from the brain of Albert Einstein, it would show no fatigue toxing at the end of the day.

    So far as the brain is concerned, it can work as well and swiftly at the end of eight or even twelve hours f efforts as at the beginning. The brain is totally tireless. So what makes us tired.

    Some scientists declare that most of our fatigue come from our mental and emotional(情感的) attitudes. One of England's most outstanding scientists. J. A. Hadfield,says,“The greater part of the fatigue from which we suffer is of mental origin. In fact,fatigue of purely physical origin is rare.” Dr. Brill, a famous American scientist, goes even further. He declares,“One hundred percent of the fatigue of a sitting worker in good health is due to emotional problems.”

    What kinds of emotions make sitting workers tired?Joy?Satifaction?No!A feeling of being bored,anger,anxiety,tenseness,worry,a feeling of nt being appreciated---those are emotions that tire sitting workers.Hard work by itself seldom causes fatigue.We get tired because our emotions produce nervousness in the body.