题干

为什么用吸管吸饮料时,饮料会被吸入嘴里?

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答案(点此获取答案解析)

用塑料吸管从瓶中吸饮料时,管内的空气被吸走,气压减小,饮料靠是在大气压的作用下被压入到嘴里的.

同类题2

小华同学配制了一定浓度的盐水,帮妈妈筛选出饱满的种子,她想知道所配制出的盐水密度,就用天平和量筒来进行测量,具体步骤如下:

⑴把天平放在水平桌面上,将____移到标尺左端的零刻线处后,发现天平横梁左高右低,应将右侧的平衡螺母向____(选填“左”或“右”)调节,使天平平衡;

⑵用调节好的天平测量空烧杯的质最m1:

⑶把配制好的盐水倒入量筒中,测量盐水体积V,如图甲所示;

⑷把量筒中的盐水全部倒入烧杯中,测量烧杯和盐水的总质量m2,如图乙所示.请根据图中数据,帮小华同学把下表填写完整:

空烧杯的质量m1/g

量筒中盐水的体积V/cm3

烧杯和盐水的总质量m2/g

盐水的密度ρ/(g·cm-3)

30

 ____

____

____

⑸以上方法测出的盐水密度值比真实值____(选填“偏大”或“偏小”);

⑹小华同学发现混杂在种子中的小石块也同饱满的种子一起沉入了盐水底部,她想知道石块的密度有多大,就选了一块大小合适且与其材质相同的石块,巧妙利用图乙所示的天平状态,按以下的步骤测出了石块的密度.

①用细线栓着石块浸没在盐水中 (石块未接触烧杯底且盐水未溢出),天平读数增大了△m1;

②将石块缓慢沉入烧杯底部,放开细线,天平读数又增大了△m2:

③石块密度的表达式ρ石(用△m1、△m2及盐水密度ρ表示)____.

同类题3

任务型阅读

    Let children learn to judge their work.____ If corrected too much, he will stop talking. He notices a thousand times a day the difference between the language he uses and the language those around him use. Bit by bit, he makes the necessary changes to make the necessary changes to make his language like other people's.____They learn to do without being taught to walk, run, climb, whistle, ride a bicycle, compare their own performances with those of more skilled people, and slowly make the needed changes.

    But in school we never give a chance to find out his mistakes and correct them by himself.____ We act as if we thought that he would never notice a mistake unless it was pointed out to him, or correct it unless he was made to. Let him work out, with the help of other children if he wants it, what this word says, what the answer is to that problem, whether this is a good way of saying or doing this or not.

    If it is a matter of the right answer, as it may be in mathematics or science, give him the answer book.____Why should we teachers waste time on such routine work?____ Let the children learn what all educated people must some day learn, how to measure their own understanding, and how to know what they know or do not know.

A. Children leant to do all the other things in the same way.

B. Let him correct his own papers.

C. Point out his mistakes.

D. We do it all for him.

E. We allow him to learn from other children.

F. A child learning to talk does not learn by being corrected all the time.

G. Our job should be to help the child when he tells us that he can't find the way to get the right answer.