（1）请观察如图所示的订书机结构，指出其中用到了哪些力学知识_爱下问搜题

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问题问答题

（1）请观察如图所示的订书机结构，指出其中用到了哪些力学知识，并举出两例填写到下面的表格内．

订书机结构	应用的物理知识
例：压柄做得宽大	增大受力面积，减小压强

（2）订书时，若订书针对书产生的压强为1×10⁸Pa，订书针与书的接触面积为2×10^-7m²，人手按压柄的压力为______N．（不考虑压柄的重力和摩擦）

答案

订书机是以转轴为支点的杠杆；

压柄做得比较宽是为了增大受力面积来减小对手的压强；

底座做得比较宽是为了增大受力面积来减小对桌面的压强；

钉尖做得尖是为了减少受力面积来增大压强；

故答案见下表：

订书机结构	应用的物理知识
例：压柄做得宽大	增大受力面积，减小压强
钉尖做得尖	为了减少受力面积来增大压强
底座做得比较宽	为了增大受力面积来减小对桌面的压强

（2）已知P=1×10⁸Pa，S=2×10^-7m²，

由P=

F

S

可得人手按压柄的压力F=PS=1×10⁸Pa×2×10^-7m²=20N．

故答案为：20．

完形填空

Once my mother told me a story that in Africa, when an antelope (羚羊) wakes up every morning, the first thing it thinks about is, “I must be 36 to run faster than the fastest lion, or I will be killed.” 37 , a lion wakes from his dream. The first thing the lion thinks about is, “I must be able to catch the 38 antelope, or I will starve to 39 .” So almost simultaneously(同时地), the antelope and the lion get up and start running toward the 40 sun.
This is 41 : full of chances and challenges. Whether you are an antelope or a lion, you must go 42 when the sun rises. For students, it is just the same. If we don’t study hard, sooner or later, we will 43 the other students. At first I didn’t know what the word “exam” 44 . Later, I knew an exam was a kind of 45 . In competitions, there are always winners and 46 . As I grew up, I got to know competition well. In one’s life, there must be competitions, so people can 47 .
Each time I saw children playing games and heard their 48 , I wished I were that age again. 49 , I remembered my parents’ words: You must work very hard for a good future. So I 50 my pen and began to study hard again.
I was still not sure what competition 51 meant. One day, I was 52_in an English-speaking competition. When I went to the stage, I saw other students looking at me kindly. Suddenly I 53 what competition was. It is not as cruel as my teacher and parents told me. In fact, competition is the 54 : it is kind and necessary.
I learned a lot from realizing this 55 . Now I understand better about the world. Competition is important for us all.

A．On the contrary

B．At the same time

C．In other words

D．In the first place

A．fall behind

D．competition

B．participating

B．acknowledged

D．consequence

单项选择题

生活性"三废"是指（）

A.废水、废气、废渣

B.污水、垃圾、粪便

C.废水、垃圾、粪便

D.废水、废渣、垃圾

E.废气、废水、垃圾