下列对牛顿第一定律的理解正确的是（） A．牛顿第一定律是_爱下问搜题

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问题选择题

下列对牛顿第一定律的理解正确的是（　　）

A．牛顿第一定律是说当弹簧的劲度系数一定时，弹簧的弹力与形变量成正比

B．牛顿第一定律表明物体有保持原来运动状态不变的性质

C．选择不同的参考系时物体的运动状态不同，但牛顿第一定律总是成立

D．可以用实验直接验证牛顿第一定律

答案

A、胡克定律是说当弹簧的劲度系数一定时，弹簧的弹力与形变量成正比，故A错误

B、牛顿第一定律表明物体有保持原来运动状态不变的性质，故B正确

C、选择非惯性参考系牛顿第一定律不成立，故C错误

D、牛顿第一定律是在实验的基础上进一步的推理概括出来的科学理论，而不能直接通过实验得出的，但能接受住实践的检验，故D错误

故选B．

完形填空

The teacher thought that hobbies were very important for every child. She 20 all her pupils to have one, and sometimes, arranged for their parents to come and 21 the work they had done as a result.
One Friday morning the teacher told the class that 22 of them who had a hobby could 23 a holiday that afternoon to get things they had 24 as parts of their hobbies ready for their parents to see the following afternoon.
So on Friday afternoon, 25 those of the pupils who had nothing to show did their usual lessons, the 26 ones who had made something were allowed to go home, on 27 that they returned before five o’clock to bring what they were going to 28 . When the afternoon lessons began, the teacher was   29 to see that Tommy was not there. He was the laziest boy in the class, and the teacher found it difficult to believe that he had a hobby. However, at a quarter to five, Tommy arrived with a   30 collection of butterflies in glass cases. 31  his teacher had admired them
and helped him to arrange them on a table in the   32 , she was surprised to see Tommy pick them up again and begin to   33 . “What are you doing, Tommy?” she asked. “Those things must   34  here until tomorrow afternoon. That’s   35  the parents are coming to see them.”
“I know they are coming then,” answered Tommy, “and I will   36  them back tomorrow, but my big brother doesn’t want them to be out of our house at night in case they are  37 .”
“But what has it got to do   38  your big brother?” asked the teacher. “Aren’t the butterflies yours?” “No,” answered Tommy. “They belong to him.” “But Tommy, you are   39  to show your own hobby here, not somebody else’s!” said the teacher. “I know that,” answered Tommy. “My hobby is watching my brother collecting butterflies.”

判断题

简单化油器工作特性之一是：若曲轴转速不变，节气门开度很小时，喉管处的真空吸力小，气流流速低，被吸出的汽油量很少而混合气很稀。