问题
应用设计题
如图所示，当人曲臂将重物端起时，人的前臂可以看作一个杠杆，请在示意图上画出F1和F2的力臂．
答案
如图所示
题目分析：支点到力的作用线的距离叫做该力的力臂。过支点O分别作力F1、F2作用线的垂线段L1、L2就是F1、F2的力臂。如图所示。
搜题请搜索小程序“爱下问搜题”
如图所示，当人曲臂将重物端起时，人的前臂可以看作一个杠杆，请在示意图上画出F1和F2的力臂．
如图所示
题目分析：支点到力的作用线的距离叫做该力的力臂。过支点O分别作力F1、F2作用线的垂线段L1、L2就是F1、F2的力臂。如图所示。
| 完形填空。 | ||||
| Many people use email to communicate with each other. If you can surf the Internet, it is a great 1 to send messages easily, quickly and as often as you like. No 2 is it necessary to find a pen or paper, not to 3 an envelope or stamp. Are we missing anything by not writing paper letters to people? Must you take the 4 of writing them if you want to receive such letters? Most people would probably answer, "No, it is a waste of paper 5 , and this is a much better system." It is hard to be against such a viewpoint. However, I would like to try. I believe that the kinds of letters people 6 to write were probably more 7 than billions of emails sent today. Of course, when it 8 to sending quick messages, email is the best. If 9 is important, email is particularly useful. 10 , if you want really to touch someone, a letter is more personal. 11 letters are the most personal. If you can type fast, you can put a lot into a letter, but it lacks (缺少) the special sense that comes from seeing the handwriting. As long as it is understandable, it doesn't matter how tidy it is. When someone sits down and just writes to you, you will 12 that when you are reading it. Though I'm a teenager, I admit that I feel too 13 to receive a letter in the mail. I love seeing my name written by hand on 14 . You make yourself a cup of coffee, sit down in a comfortable place, open your 15 , and enjoy everything that the person puts into those words just for you. What a gift! | ||||
|