问题 选择题

探究“摩擦力的大小与什么因素有关”的三次实验如图所示。实验时,让木块在水平木板(或棉布)上做匀速运动。下列说法正确的是

A.比较甲、乙两图实验情景,可知摩擦力的大小跟作用在物体表面的压力无关

B.比较乙、丙两图实验情景,可知摩擦力的大小只跟作用在物体表面的压力有关

C.比较甲、丙两图实验情景,可知摩擦力的大小跟接触面的粗糙程度有关

D.比较乙、丙两图实验情景,可知摩擦力的大小只跟接触面的粗糙程度有关

答案

答案:C

题目分析:A、比较甲、乙两图,接触面都是木板,接触面的粗糙程度相同,甲图中木块对水平木板的压力小,摩擦力小,乙图中木块对水平木板的压力大,摩擦力大,说明摩擦力的大小与压力大小有关,因此该选项说法错误.

B、比较乙、丙两图,接触面和压力大小都不相同,摩擦力的大小也不相同,有两个变量,不符合控制变量法的思想,无法确定摩擦力的大小与压力有关,还是与接触面的粗糙程度有关,因此该选项说法错误.

C、比较甲、丙两图,木块对接触面的压力大小相同,甲图中木块对水平木板接触,接触面粗糙程度小,摩擦力小,丙图中木块与棉布面接触,接触面粗糙程度大,摩擦力大,说明摩擦力的大小与接触面的粗糙程度有关,因此该选项说法正确.

D、比较乙、丙两图,接触面和压力大小都不相同,摩擦力的大小也不相同,有两个变量,不符合控制变量法的思想,无法确定摩擦力的大小与压力有关,还是与接触面的粗糙程度有关,因此该选项说法错误.

故选C.

点评:关键是我们的实验分析能力,影响摩擦力大小的因素是初中物理中一个重要的知识,也是中考的热点之一,需要牢牢掌握.

阅读理解

阅读理解。

     When I was at university, I studied very hard. But a lot of my friends did very little work. Some did

just enough to pass the exams. Others didn't do quite enough. Fred Baines was such a student. He spent

more time drinking in the Tea House than working in the library.

     Once at the end of the term, we had to take an important test in Chinese. The test had 100 questions.

Beside each question we had to write "True" or "False". While I was studying in my room the night before

the test, Fred was watching TV. Fred usually worried a lot the night before a test. But on that night he

looked very easy. Then he told me of his idea."

     It's very simple. There are 100 questions and I have to get 50 right to pass the test. I'll take a coin into

the room. I haven't studied a Chinese book for months, so I'll toss (掷,扔) the coin. In that way, I'm sure

I'll get half of the questions right."

     The next day, Fred came happily into the examination room. As he sat tossing a coin for half an hour,

he wrote down his answers. Then he left, half an hour before the rest of us.

     The next day, Fred met his Chinese teacher at the school gate. "Oh, good, "he said. "Have you got the

results of the test?" The teacher looked at him and smiled, "Ah, it's you, Baines. Just a minute." Then the

teacher reached his pocket and took out a coin. He threw it into the air, caught in his hand and looked at

it. "I'm sorry, Baines, you failed!".

根据短文内容,判断下列句子是否正确,对的写"T",错的写"F"。

( )1. Fred Baines was a hard-working student.

( )2. They had to take a Chinese test.

( )3. Fred usually worried a lot the night before a test.

( )4. Fred thought hard and wrote down his answers.

( )5. Fred passed the test at last

填空题