沪教版2019-2020学年八年级下学期学科竞赛英语试卷（II ）卷
姓名:________ 班级:________ 成绩:________
一、单项选择。 (共20题；共40分)
1. （2分）Which of the following underlined parts is different in pronunciation from the others?
A . Relax and take a deep breath.
B . Demand for water will increase.
C . Heat the milk on the oven.
D . He's a bright kid and eager to learn.
2. （2分）That good news made all of us .
A . excited
B . exciting
C . excite
D . to excite
3. （2分）— I believe we've met here before.
— No, ________. It's the first time I've been here.
A . it isn't the same
B . it's true
C . I don't think so
D . I believe so
4. （2分）Can you help me ________ my homework?
A . of
B . with
C . to
D . for
5. （2分）一 Her job is to look after the baby.
一 You mean she's a baby-sitter?
A . take care of
B . wake up
C . make fun of
6. （2分）— Did you listen to Li Yundi _____ the piano yesterday evening?
— Yes. He played _____ and all the audience clapped loudly at the end.
A . play; perfectly
B . play; perfect
C . to playing; perfectly
D . to playing; perfect
7. （2分）, we saw the sun rise on top of Mount Taishan.
A . Lucky
B . Luckily
C . Unlucky
D . Unluckily
8. （2分）—Would you like some ?
—I'm not thirsty. Thanks. But I'd like some to eat.
A . orange; orange
B . oranges; orange
C . oranges; oranges
D . orange; oranges
9. （2分）There are sixty students in our class, of them girls.
A . Third fifths ; is
B . Third fifth ; are
C . Three fifth ; is
D . Three fifths ; are
10. （2分）Students ought _____ the truth.
A . to tell
B . tell
C . telling
D . told
11. （2分）My grandfather _________the Party since he was eighteen years old.
A . has been a member of
B . joined
C . has joined
D . join
12. （2分）I like my school. Our teachers are all to us.
A . kind
B . kinds
C . friend
D . glad
13. （2分）Hearing the director's " !", all the actors and actresses kept in the own position (位置) and waited carefully.
A . Action
B . Take two
C . Stand by
D . Good take
14. （2分）I think not difficult English every morning．
A . that，keep to read
B . it's，keep to reading
C . that，to keep reading
D . it，to keep reading
15. （2分）—You haven't cleaned your bedroom, have you?
—. I've been busy talking with John on the phone all the morning.
A . No, I haven't
B . Yes, I have
C . No, I have
D . Yes, I haven't
16. （2分）These questions are than those ones.
A . more easier
B . much easy
C . as easy
D . much easier
17. （2分）—you ever to Egypt ?
—Yes , twice. The Pyramids are really full of history.
A . Have , gone
B . Have , been
C . Did , go
D . Were , going
18. （2分）—Look at the photos ________ my family.
—Let me see. Who is the boy ________ the first photo?
A . in; to
B . of; in
C . for; on
D . for; to
19. （2分）Don't return the book to Tina, please. I _______ it yet.
A . don't read
B . wasn't reading
C . haven't read
20. （2分）— May I use (使用) your pen?
— Sure. ________
A . Here you are.
B . Here are you.
C . You are here.
D . Here we are.
二、完形填空。 (共1题；共15分)
21. （15分）阅读下文，掌握其大意，然后从各题所给的四个选项中选出一个最佳答案。
Three1ago, my family got our first computer. 2 the beginning of this summer, I found it was too old and I wanted to get a 3 one. After my father and I talked for a long time, he 4 . We went to many shops and read many ads 5 we bought an HP computer.
During the first week, I noticed 6 our computer had some problems. I spent many hours 7 to fix it, but it 8 work. So I 9 to phone the HP company and ask them 10 to work out my problem. They told me to wait until the next morning because all their workers were 11 that day.
The next morning two workers came. It took them many hours to mend it, but the computer 12 did not work. My dad had no other way but to return the whole thing. A few days later, we decided that I should go on the Internet and order some parts to build a new computer by 13 .
It was not an easy job for me to build a new computer. I tried many times, and in the end I was successful. From these setbacks(挫折), I have learned a lot. Now I believe that if the HP computer hadn't had any problems, 14 I would not have learned how to build the new one. Even though I spent lots of time on it, I know it wasn't 15.
（1）
A . days
B . weeks
C . months
D . years
（2）
A . At
B . On
C . To
D . For
（3）
A . big
B . new
C . cheap
D . small
（4）
A . won
B . paid
C . agreed
D . received
（5）
A . At first
B . At last
C . At once
D . At times （6）
A . if
B . that
C . what
D . how （7）
A . try
B . tried
C . to try
D . trying （8）
A . do
B . did
C . don't
D . didn't （9）
A . hoped
B . have
C . had
D . liked （10）
A . how
B . what
C . why
D . where
（11）
A . free
B . sad
C . busy
D . exciting
（12）
A . already
B . always
C . still
D . usually
（13）
A . themselves
B . himself
C . itself
D . myself
（14）
A . or
B . then
C . so
D . and
（15）
A . a waste of time
B . a successful job
C . a good computer
D . a bad company
三、阅读理解。 (共5题；共39分)
22. （8分） Happy Farm is an online game. It is very popular among people in China. The game offers you a piece of empty land and some seeds (种子) at first. You are like the farmer. If your land is small, you can spend some money to make it big. And you must harvest your things on the farm on time, or some other farmers will steal your fruits, vegetables, milk, eggs and so on. Of course, you can steal
theirs. If you want to make money, you must sell your things out.
Some Chinese websites have offered this game to its users. So far, it is said that about 16 million Chinese people are playing this game. Some people were so crazy (疯狂的) that they even get up in the midnight to harvest their crops and steal others’.
Happy Farm brings happiness to people. It is really a fascinating game. But it also brings many problems. It is reported that a baby died in a hospital just because the doctor didn't give him timely treatment. Do you know what the doctor was doing? He was playing Happy Farm! There are many stories like this.
（1）According to this passage, what is very popular in China?
A . The farmer
B . Happy Farm
C . The Chinese website
D . The Doctor
（2）Which is the right order to play the game Happy Farm?
a. Plant some crops.
b. Harvest your crops on time.
c. Sell your things out.
d. Get land and some seeds.
A . d-b-c-a
B . a-d-c-b
C . d-a-b-c
D . c-d-a-b
（3）Many people are so involved in the game Happy Farm that they get up in the midnight _____.
A . to harvest and steal crops
B . to chat with others
C . to sell their things out
D . to read news about this game
（4）What does the writer think of this game?
A . It is not interesting at all.
B . People shouldn't be crazy about it.
C . People must get up early to steal crops.
D . People may play it when they are at work.
23. （8分） On the fifth day of the fifth month of the Chinese lunar calendar（农历）,
which is Wednesday this year, all Chinese celebrate one of their traditional festivals, the Dagon Boat Festival, or Dragon Boat Festival. Their celebrations include eating zongzi, rice wrapped in bamboo leaves in the shape of a pyramid, racing dragon boats and sticking mugwort leaves on their doors.
In 2007, the central government decided to add the Dragon Boat Festival, together with two other traditional festivals - Tomb Sweeping Day (清明节) and Mid Autumn Festival - to the list of public holidays
According to tradition, our ancestors（长辈） believed the hot weather in midsummer might cause different kinds of diseases (疾病). So, to keep off diseases and drive out evil were the main purposes of the Dragon Boat Festival. Parents used colorful threads to make necklaces and bracelets （手镯） for children, gave them beautiful embroidered bags（荷包）, painted the Chinese character for "king" (wang) on their foreheads to drive away bad luck. The Dragon Boat Festival was also called "kids festival" in some places. Spending such happy hours with parents, young children began to understand the festival as well as the traditions and culture behind it. Repeating the customs year by year makes it possible for kids to learn the traditions, accept it and pass it on when they become adults.
（1）How do people celebrate the Dragon Boat Festival?
A . People celebrate this festival by eating eggs.
B . People celebrate this festival by eating zongzi, racing dragon boats.
C . People celebrate this festival by sending cards.
D . People celebrate this festival by singing and dancing.
（2）What is the Chinese meaning of “mugwort leaves” in the second paragraph?
A . 粽叶
B . 红叶
C . 艾叶
D . 松叶
（3）How many public holidays added by the central government in 2007?
A . 2
B . 3
C . 4
D . only one
（4）What is the main purpose of the Dragon Boat Festival according to tradition?
A . To keep off diseases and drive out evil and bad luck
B . To spend happy time with parents.
C . To make necklaces and bracelets for children
D . To have a long holiday with family members.
24. （8分）阅读理解
A young woman turns around and around quickly, and jumps high. In the background, a young girl reads a rejection(拒绝)letter from a ballet school." You have the wrong body for ballet," it says, " and at thirteen, you are too old." This was one of the most popular advertisements(广告)of 2014 and it describes American Ballet Theatre's principal(主要的)dancer Misty Copeland.
This was not a real letter. But Copeland says it is very similar to letters from her childhood. While many dancers start at the age of three, Copeland only began to study ballet in 1995 as a thirteen-year-old girl. People often told her that she was too old，or that she didn't have the perfect body type(She is only 157 cm tall). Her family moved a lot, and it was sometimes difficult for her to attend ballet classes. But Copeland loved dancing and did not want to give up. She stayed with her ballet teacher during the week and spent time with her family only at the weekend. This was a difficult life, but she worked hard and won her first national competition when she was fourteen years old. Copeland joined the American Ballet Theatre in 2000 and performed in many ballets over the next few years. In 2007, she became a solo(单独的) performer, and in 2015 she became its principal dancer.
Copeland is now a dancer, author and Broadway performer. She also starred in the 2015 film A Ballerina's Tale. So what's next? According to Copeland, anything is possible：My career(职业)really is just now beginning.
（1）How old was Copeland when she became the principal dancer?
A . 13.
B . 14.
C . 25.
D . 33.
（2）Why was it difficult for Copeland to attend ballet classes?
A . Because her family moved a lot.
B . Because she was not a good dancer.
C . Because she had no invitation letter.
D . Because she had the wrong body type.
（3）Which of the following is TURE according to the passage?
A . Copeland became successful because of the advertisement.
B . Copeland had to spend a lot of time away from her parents.
C . Copeland won her first national competition as a solo performer.
D . Copeland has ended up her career as an actress on Broadway.
（4）What's the writer's opinion of Copeland?
A . Copeland sets an example who never gives up.
B . Copeland was too old to start ballet at thirteen.
C . Copeland has made her achievements by accident.
D . Copeland was lucky to get support from the ballet school.
25. （10分）阅读理解
I am an apple. You can find me growing（生长） in many places（地方） in the world. I am like my cousins, pears and bananas. I am more round than a pear, and bananas are longer than I. I am delicious （美味的）, so people all over the world like to eat me. I cost very little money and I help make people healthy. There is a saying in English : An apple a day keeps the doctor away. Don't you think I'm great?
（1）The bananas is _______ than the apple.
A . shorter
B . longer
C . more round
D . more delicious
（2）The best title of the passage is_____
A . All kinds of fruits
B . Apples are delicious
C . An apple a day keeps the doctor away
D . Apples
（3）The banana is the apple's ______.
A . brother
B . father
C . sister
D . cousin
（4）Here the underlined word “saying” means_______ in Chinese.
A . 说话
B . 谚语
C . 言语
D . 语言
（5）The underlined sentence means ______.
A . the doctor goes away when he sees an apple
B . the doctor runs away when you give him an apple
C . you eat an apple every day and you can be healthy
D . eating an apple every day can help the doctor a lot
26. （5分）任务型阅读
B. She is the one who sells the candy
C. It's the heat that kills it
D. Everything you told me went in one ear and out the other
E. This boy cried so terribly that he scared four other patients out of the office
四、单词拼写。 (共6题；共15分)
27. （1分）Look at these ________ (图画). They are very nice.
28. （1分）This is a photo of my sister and she is ________ (十九) years old.
29. （1分）What he said has ________/ 'influ?nst/ many students now.
30. （1分）We have some ________ at home.
31. （10分）根据下列句子及所给汉语注释或通过上下文，在答题卡上标有题号的横线上，写出空缺处各单词的正确形式。每空只写一词。
（1）More and more Chinese people are able to________ (付得起)to travel abroad.
（2）He was wearing a very________ (严肃的)expression and I knew something was wrong.
（3）Regular tests help the teacher to learn about the________ (进步)of each student.
（4）He________(承诺)that he would come, but he has not turned up yet.
（5）Among the many________ （业余爱好）of his are reading, music and tennis.
（6）There is nothing there - you are just________ (想象)things!
（7）The little girl walked________ (自信地)onto the stage, ready for her first speech.
（8）-Can I help you with it?-I am grateful for your offer, but I can manage it________ ．
（9）- Did you catch________I said?- Sorry. I was answering a text message just now.
（10）- It's no use having________ only.- Don't worry. Peter can show you how to turn an idea into an act.
32. （1分）Every night h________ of old people dance at the square near our house.
五、选词填空。 (共1题；共10分)
33. （10分）阅读短文，从方框中选择恰当的词并用其适当形式填空，使短文完整、通顺。每词限用一次。
"I sold meat this morning and got 100 coins (硬币). Then I had a short ________But when I woke up, I couldn't find my money," said the boy.
Bao Gong looked the boy up and down and ________ for some time. Then he pointed at a horse and said it was the thief (小偷). He shouted at the horse and asked it to give the boy's ________back.
People around laughed and said quietly, "What is he doing? Shouldn't Bao Gong be ________ Bao Gong heard that and shouted, "How could you say bad words ________an official? You are all .fined (被罚款) one coin" Then he took out a large bowl full of ________ And asked everyone to put a coin into it.
When one man put his into the bowl, Bao Gong said, "This is the ________thief! When he put the coin into the bowl, there was a film of oil (一层油) on the water. All the boy's corns have oil from the meat on________
At last the boy got his money back. Everyone said that Bao Gong was a really smart man.
六、书面表达。 (共1题；共5分)
34. （5分）假如你是王平，你的英国笔友Cathy发来邮件说她在 "Reading Week"时读了几本有趣的书，她想跟你交流一下，了解你的读书情况。请你根据她的问题回复邮件。
提示词语：books on, because, get, knowledge
要求： 70词左右；不得出现真实的校名和人名。
Glad to receive your letter and I'm happy to tell you something about me.
参考答案一、单项选择。 (共20题；共40分)
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二、完形填空。 (共1题；共15分)
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三、阅读理解。 (共5题；共39分)
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四、单词拼写。 (共6题；共15分) 27-1、
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五、选词填空。 (共1题；共10分)
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六、书面表达。 (共1题；共5分)
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上海市沪教版八年级数学上下册知识点梳理 第十六章 二次根式 第一节 二次根式的概念和性质 二次根式 1． 二次根式的概念: 式子)0(≥a a 叫做二次根式．注意被开方数只能是正数或0。 2． 二次根式的性质 ①???≤-≥==) 0()0(2a a a a a a ； ②)0()(2≥=a a a ③)0,0(≥≥?=b a b a ab ； ④ )0,0(>≥=b a b a b a ; 最简二次根式与同类二次根式 1. 被开方数所含因数是整数，因式是整式，不含能开得尽方的因数或因式的二次根式，叫做最简二次根式． 2.化成最简二次根式后，被开方数相同的二次根式，叫做同类二次根式 二次根式的运算 1.二次根式的加减:先把各个二次根式化成最简二次根式，再把同类三次根式分别合并． 2.二次根式的乘法:等于各个因式的被开方数的积的算术平方根， 即 ).0,0(≥≥=?b a ab b a 3.二次根式的和相乘，可参照多项式的乘法进行． 两个含有二次根式的代数式相乘，如果它们的积不含有二次根式，那么这两个三次根式互为有理化因式． 4.二次根式相除，通常先写成分式的形式，然后分子、分母都乘以分母的有理化因式，把分母的根号化去(或分子、分母约分)．把分母的根号化去，叫做分母有理化． ~ 二次根式的运算法则： =(a+b) ≥0) ).0,0(≥≥=?b a ab b a =a ≥0,b>0） n =≥0)
第十七章 一元二次方程 一元二次方程的概念 1．只含有一个未知数，且未知数的最高次数是2的整式方程叫做一元二次方程 2．一般形式y=ax 2+bx+c （a ≠0），称为一元二次方程的一般式，ax 叫做二次项,a 是二次项系数；bx 叫做一次项，b 是一次项系数；c 叫做常数项 一元二次方程的解法 … 1．特殊的一元二次方程的解法：开平方法，分解因式法 2．一般的一元二次方程的解法：配方法、求根公式法 3．求根公式2b x a -±=：1222b b x x a a ---= , = ； △=2 4b ac -≥0 一元二次方程的判别式 1．一元二次方程20(0)ax bx c a ++=≠： △＞0时，方程有两个不相等的实数根 △＝0时，方程有两个相等的实数根 △＜0时，方程没有实数根 2．反过来说也是成立的 ) 一元二次方程的应用 1．一般来说，如果二次三项式2ax bx c ++（0a ≠）通过因式分解得2ax bx c ++=12()()a x x x x --；1x 、2x 是一元二次方程20(0)ax bx c a ++=≠的根 2．把二次三项式分解因式时； 如果2 4b ac -≥0，那么先用公式法求出方程的两个实数根，再写出分解式 如果24b ac -＜0，那么方程没有实数根，那此二次三项式在实数范围内不能分解因式 3． 实际问题：设，列，解，答 第十八章 正比例函数和反比例函数 ．函数的概念 1．在问题研究过程中，可以取不同数值的量叫做变量；保持数值不变的量叫做常量 2．在某个变化过程中有两个变量，设为x 和y ，如果在变量x 的允许取之范围内，变量y 随变量x 的变化而变化，他们之间存在确定的依赖关系，那么变量y 叫做变量x 的函数，x 叫做自变量 % 3．表达两个变量之间依赖关系的数学是自称为函数解析式()y f x = 4．函数的自变量允许取之的范围，叫做这个函数的定义域；如果变量y 是自变量x 的函数，
上海市沪教版八年级数学上下册知识点梳理 第十六章二次根式 第一节二次根式的概念和性质 16.1 二次根式 1．二次根式的概念: 式子a(a 0) 叫做二次根式．注意被开方数只能是正数或0。 2．二次根式的性质 2 a(a 0) ① a a ；a(a 0) ②( a)2 a(a 0) ③ab a b(a 0,b 0) ； ④ a a (a 0,b 0) bb 16.2 最简二次根式与同类二次根式 1. 被开方数所含因数是整数，因式是整式，不含能开得尽方的因数或因式的二次根式，叫做最简二次根式． 2. 化成最简二次根式后，被开方数相同的二次根式，叫做同类二次根式 16.3 二次根式的运算 1. 二次根式的加减: 先把各个二次根式化成最简二次根式，再把同类三次根式分别合并． 2. 二次根式的乘法:等于各个因式的被开方数的积的算术平方根， 即a b ab(a 0,b 0). 3. 二次根式的和相乘，可参照多项式的乘法进行． 两个含有二次根式的代数式相乘，如果它们的积不含有二次根式，那么这两个三次根式互为有理化因式． 4. 二次根式相除，通常先写成分式的形式，然后分子、分母都乘以分母的有理化因式，把分母的根号化去( 或分子、分母约分) ．把分母的根号化去，叫做分母有理化． 二次根式的运算法则： a c + b c =(a+b) c (c 0) a b ab(a 0,b 0). aa ) b b(a 0,b>0 ( a)n a n( a 0) 第十七章一元二次方程
△=b 2 4ac ≥0 17.3 一元二次方程的判别式 2 1．一元二次方程 ax bx c 0(a 0) ： △> 0时，方程有两个不相等的实数根 △＝ 0 时，方程有两个相等的实数根 △< 0 时，方程没有实数根 2．反过来说也是成立的 17.4 2．把二次三项式分解因式时； 如果 b 2 4ac ≥ 0，那么先用公式法求出方程的两个实数根，再写出分解式 2 如果 b 2 4ac < 0，那么方程没有实数根，那此二次三项式在实数范围内不能分解因式 3． 实际问题：设，列，解，答 第十八章 正比例函数和反比例函数 18.1．函数的概念 1．在问题研究过程中，可以取不同数值的量叫做变量；保持数值不变的量叫 做常量 2．在某个变化过程中有两个变量，设为 x 和 y ，如果在变量 x 的允许取之范围内，变量 y 随变量 x 的变化而变化，他们之间存在确定的依赖关系，那么变量 y 叫做变量 x 的函数， x 叫做自变量 3．表达两个变量之间依赖关系的数学是自称为函数解析式 y f (x) 4．函数的自变量允许取之的范围， 叫做这个函数的定义域； 如果变量 y 是自变量 x 的函数， 那么对于 x 在定义域内去顶的一个值 a ，变量 y 的对应值叫做当 x=a 时的函数值 18.2 正比例函数 1． 如果两个变量每一组对应值的比是一个不等于零的常数， 那么就说这两个变量成正比例 2．正比例函数 :解析式形如 y=kx ( k 是不等于零的常数)的函数叫做正比例函数，气质常数 k 叫做比例系数；正比例函数的定义域是一切实数 17.1 一元二次方程的概念 1．只含有一个未 知数，且未知数的最高次数是 般形式 y=ax2+bx+c (a ≠ 0)，称为 次项系数； 2． 系数； bx 叫做一次项， b 是一 17.2 一元二次方程的解 法 1．特殊的一元二次方程的 解法： 2．一般的一元二次方程的解法： 2 的整式方程叫 做 元二次方程的一般式， c 叫做常数项 元二次方程 ax 叫做二次项 ,a 是二次 项 开平方法， 配方法、求根公式法 分解因式法 2 b b 2 4ac 3．求根公式 x ： x 1 b b 2 4ac 2a x 2 b b 2 4ac 2a 元二次方程的应用 1． 般来说，如果二次三项式 ax 2 bx c 0) 过因 式分解 2 ax bx c = a(x x 1)(x x 2) ； x 1、 x 2 是一元二 次方程 2 ax bx 0(a 0) 的根
班级_________ 姓名________ 家长签字__________ 一正确书写字母和单词 G K a w y U slide hippo run desk 二写出下列字母的左右邻居. 1.__ c __ 2.__ j __ 3.___P __ 4. ___ W__ 5. __ t __ 三看图,选出正确的字母填空 1. 2. 3. 4. __and f__y __ig __ight ( a e i ) ( m l n ) ( b p d ) ( a e i ) 5. 6. 7. 8. s__ n __poon bo___ rabbi__ ( a e u ) ( s t w ) ( s x t ) ( t d b ) 9.10. 11. 12 swi__ ba__ __late __ion ( m l n) (r g t ) (b p t) ( h y l)
四看图圈出正确的单词或词组. 1. 2. 3. write run bee insect three lions ten lions 4. 5. 6 . chair desk bear panda sun star 五圈出不同类的单词 1.swim run fly chair 2.mouse insect lion fox 3.bowl plate bear plate 4.four ten table seven 5.chair big desk bag 6.long short seesaw fat 六连线,选出正确的答句 1.How are you? A. It’s yellow. 2.Can you see the moon? B. Yes, she is. 3.What colour is it? C. OK, Dad. 4.Is she your sister? D. I’m fine. Thank you. 5.Put the bag on the desk,please. E. No, I can ’t.
第1课时二次根式的概念 1．了解二次根式的概念；(重点) 2．理解二次根式有意义的条件；(重点) 3．理解a(a≥0)是一个非负数，并会应用a(a≥0)的非负性解决实际问题．(难点) 一、情境导入 1．小明准备了一张正方形的纸剪窗花，他算了一下，这张纸的面积是8平方厘米，那么它的边长是多少？ 2．已知圆的面积是6π，你能求出该圆的半径吗？ 大家在七年级已经学习过数的开方，现在让我们一起来解决这些问题吧！ 二、合作探究 探究点一：二次根式的概念 【类型一】二次根式的识别 (2015·安顺期末)下列各式：①1 2；②2 x；③x2＋y2；④－5；⑤35， 其中二次根式的个数有( ) A．1个B．2个C．3个D．4个 解析：根据二次根式的概念可直接判断，只有①③满足题意．故选B. 方法总结：判断一个式子是否为二次根式，要看式子是否同时具备两个特征：①含有二次根号“”；②被开方数为非负数．两者缺一不可． 变式训练：见《学练优》本课时练习“课堂达标训练”第2题 【类型二】二次根式有意义的条件 代数式 x＋1 x－1有意义，则x的取值范围是( ) A．x≥－1且x≠1 B．x≠1 C．x≥1且x≠－1 D．x≥－1 解析：根据题意可知x＋1≥0且x－1≠0，解得x≥－1且x≠1.故选A. 方法总结：(1)要使二次根式有意义，必须使被开方数为非负数，而不是所含字母为非负数；(2)若式子中含有多个二次根式，则字母的取值必须使各个被开方数同时为非负数； (3)若式子中含有分母，则字母的取值必须使分母不为零．
变式训练：见《学练优》本课时练习“课堂达标训练”第4题 探究点二：利用二次根式的非负性求值 【类型一】 利用被开方数的非负性求字母的值 (1)已知a ，b 满足2a ＋8＋|b －1|＝0，求2a －b 的值； (2)已知实数a ，b 满足a ＝b －2＋2－b ＋3，求a ，b 的值． 解析：根据二次根式的被开方数是非负数及绝对值的意义求值即可． 解：(1)由题意知???2a ＋8＝0，b －1＝0， 得2a ＝－8，b ＝1，则2a －b ＝－9； (2)由题意知? ??b －2≥0，2－b ≥0，解得b ＝2.所以a ＝0＋0＋3＝3. 方法总结：①当几个非负数的和为0时，这几个非负数均为0；②当题目中，同时出现a 和－a 时(即二次根式下的被开方数互为相反数)，则可得a ＝0. 变式训练：见《学练优》本课时练习“课堂达标训练”第8题 【类型二】 与二次根式有关的最值问题 当x ＝________时，3x ＋2＋3的值最小，最小值为________． 解析：由二次根式的非负性知3x ＋2≥0，∴当3x ＋2＝0即x ＝－23 时，3x ＋2＋3的值最小，此时最小值为3.故答案为－23 ，3. 方法总结：对于二次根式a ≥0(a ≥0)，可知其有最小值0. 变式训练：见《学练优》本课时练习“课后巩固提升”第8题 三、板书设计 本节课的内容是在我们已学过的平 方根、算术平方根知识的基础上，进一步引入二次根式的概念．教学过程中，应鼓励学生积极参与，并让学生探究和总结二次根式在实数范围内有意义的条件
沪教版2020年八年级下学期英语开学考试试卷B卷 一、完形填空 (共1题；共10分) 1. （10分） Who taught you to walk when you were little? Who worries the most when you are 1 ? Who makes you dinner? It’s 2mother. No matter what happens, she'll 3 the love for you. Do you know how 4 Day came into being（产生）? It began in the US in 1907 when an American girl 5Anna Jarivs started a campaign to honor（给…荣誉）mothers. She believed that mothers could 6 people to get over the pain of the war and to strengthen（加强）the relationship inside families. On Mother's Day, children usually help their mothers do 7 . In western countries, bringing mothers 8in bed is common. A mother will get up late 9her children make her favorite breakfast. Children also make their own Mother's Day card 10a thank-you note. Or they buy gifts and flowers for their mothers. （1） A . lazy B . ill C . sleepy （2） A . his B . your C . her （3） A . continue B . stop C . start （4） A . Children's B . Women's C . Mother's （5） A . named B . names
牛津英语二年级英语语法习题集 、There be 句型: (1) There be 句型由There is 或There are 引导，表示 在…地方有 …东西 (2) There is + 单数或不可数名词； There are + 复数 (3) There be 句型遵循 就近原则” There is a table and two chairs in the room. There are two chairs and a table in the room. 填写：am, is, are 1. _ you a boy? No, I ____ a girl. 2. He ___ m y father. He ___ t all. 3. What colour ___ the rabbit? It ___ white. 4. What colour ___ the dogs? They _____ brow n. 5. There __ a bowl in the box. 6. There ____two bowls in the box. 7. There __ some water in the bowl. 8. There __ some apples on the table. 9. There __ a plate and three spo ons on the table. 10. There __ three spo ons and a plate on the table. 、Be 动词 am, is, are 填写 be 动词：am, is, are 1.1 ___ D a nny. You ___ Mary. 2. I ___ tall. You ___ short. 3.She ___ my mother. She ___ fat. 4.He __ my brother. He __ small. 、介词：in 在…里面, on 在…上面，under 在…下面 填写介词：in, on, un der, at, up, to 1.look ___ 2. liste n ___ 3. pick ____ 4. ___ the room 5. ____ the bowl 6. ____ sit ______________ t he chair 7. ______ the plate 8. the floor 9. the seesaw 10. __ the zoo11. ___ the park 12. the childre n s garden13.__ the sky Be 动词用法口诀：我是 am,你是are 。is 用于他她它，凡是复数都用 are 。
M1U1： green yellow blue purple white pink orange brown black red grey what colour beautiful rainbow see shine shining shiny butterfly outside inside umbrella van window box yellow zebra hand insect five girl rabbit butterflies mouse net orange pig queen
soup table I my you your he his she her it its they their pear rabbit bird apple bag dog elephant jar kite lion What colour is it It’s pink. over there What colour are they They are yellow. What can you see I can see a butterfly.
watch bag soft hard rough smooth touch feel open close tall short fat thin long young old big small new Is it a watch Yes it is. / No it’s a pencil case. Do you like it Yes. What is it It’s a bag.
Train bus car van taxi bicycle bike ship can can't hear listen what outside inside beside tiger cat dog red down up bus stop here come go station wait for road beside the window Is it smooth Yes it is. /No it’s rough.What is it It’s a van.
沪科版八年级数学下知识点总结 二次根式知识点： 知识点一：二次根式的概念 形如（）的式子叫做二次根式。 注：在二次根式中，被开放数可以是数，也可以是单项式、多项式、分式等代数式，但 必须注意：因为负数没有平方根，所以是为二次根式的前提条件，如，，等是二次根式，而，等都不是二次根式。 知识点二：取值范围 1. 二次根式有意义的条件：由二次根式的意义可知，当a≧0时，有意义，是二次根式，所以要使二次根式有意义，只要使被开方数大于或等于零即可。 2. 二次根式无意义的条件：因负数没有算术平方根，所以当a﹤0时，没有意义。 知识点三：二次根式（）的非负性 （）表示a的算术平方根，也就是说，（）是一个非负数，即0（）。注：因为二次根式（）表示a的算术平方根，而正数的算术平方根是正数，0的算术平方根是0，所以非负数（）的算术平方根是非负数，即0（），这个性质也就是非负数的算术平方根的性质，和绝对值、偶次方类似。这个性质在解答题目时 应用较多，如若，则a=0,b=0；若，则a=0,b=0；若，则a=0,b=0。知识点四：二次根式（）的性质 （） 文字语言叙述为：一个非负数的算术平方根的平方等于这个非负数。 注：二次根式的性质公式（）是逆用平方根的定义得出的结论。上面的公式 也可以反过来应用：若，则，如：，. 知识点五：二次根式的性质 文字语言叙述为：一个数的平方的算术平方根等于这个数的绝对值。 注： 1、化简时，一定要弄明白被开方数的底数a是正数还是负数，若是正数或0，则等于a本身，即；若a是负数，则等于a的相反数-a,即； 2、中的a的取值范围可以是任意实数，即不论a取何值，一定有意义； 3、化简时，先将它化成，再根据绝对值的意义来进行化简。 知识点六：与的异同点 1、不同点：与表示的意义是不同的，表示一个正数a的算术平方根的平方，而表示一个实数a的平方的算术平方根；在中，而中a可以是正实数，
沪教版2019-2020学年八年级下学期英语期末考试试卷（I）卷 姓名:________ 班级:________ 成绩:________ 一、从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。 (共15题；共30分) 1. （2分）man in a black hat is my PE teacher. He often plays football with us. A . A; the B . The; a C . The; / D . A; / 2. （2分）He made a lot of mistakes in the exam his carelessness. A . because B . as C . because of 3. （2分）________ you are so weak, you'd better stay at home. A . Since B . For C . Because D . Though 4. （2分）---Did you watch the basketball match yesterday? ---Yes. We were all ____about the ___match. A . exciting, excited B . exciting, exciting C . excited, excited D . excited, exciting, 5. （2分）--- Could you please my pet dog for a few days when I am away on business? --- No problem. A . look for B . care for
沪教版牛津英语二年级下册抄写句子 二年级英语作业 一抄写下列单词和句子注意大小写及标点符号。 autumn winter cool cold season bus zebra brown zoo fish wolf van five giraffe snake elephant black hand hen salad carrot chicken banana frog skate hop ride a bicycle skip kite book girl run purple sun tiger cat dog red train car ship pig bag pink table watch soft hard rough smooth white orange What colour are they? They are white Touch the bag Is it smooth? No It’s rough Listen! What can you hear? I can hear a ship Do you like running? Yes I like running What do you like eating? I like eating salad What are they? They are zebras
Do you like giraffes, Kitty? No, I don’t I like swimming in the water 二选出不同类的单词写序号。 ( )1 A bag B write C rubber ( )2 A ride B rice C write ( )3 A boy B big C small ( )4 A cola B juice C zebra ( )5 A can B hear C see ( )6 A hard B soft C head ( )7 A spring B summer C season ( )8 A skip B ship C skate ( )9 A carrot B chicken C can ( )10 A ship B soft D short 结束语 1、同学们，老师相信，在你们当中一定有未来的高斯、笛卡儿，只要积极动脑，做生活的有心人，你们一定会为人类的发展做出巨大的贡献，创造出巨大的财富，有信心吗？ 2、同学们，科学的殿堂美不胜收，只要大家以勤为径，每个人都能领略到无限美好的风光。 3、一分耕耘，一分收获，同学们，体验到成功的喜悦了吗？ 4、珍惜时间就等于珍惜生命。让我们每个热爱生命的人都去珍惜每分、每秒，好吗？ 5、同学们，大家想过吗？为什么人民币的面值只有１分、２分、５分、１角、２角、５角、１元、２元、５元……而没有３分、４分、６分、７分呢？这虽然是个小问题，老师相信，聪明的你们一定能研究出大学问！ 6、同学们，生活中时时刻刻有数学，事事有数学，因此，我们应该爱数学、学数学、用数学。 7、你有哪些新收获？你是怎样获取这些知识的？你还有什么疑难问题？谁来帮她解决？ 8、今天，我们通过自己的努力，发现并学会了这么多知识，老师真为你们骄傲！其实生活中有更多的知识等着你们去发现、探索，快做个有心人吧，你会成长得更快！ 9、同学们，与数学王国的人交朋友吧，它会让你领略到宇宙的神奇与奥妙! 10、同学们，我们好多知识都是前人经过无数次实验总结出来的。老师希望你们在今后的学习中不断探索，获取更多知识，好吗？ 11、没有最好，只有更好。老师相信，下节课同学们一定会表现得更出色。 12、这节课有许多知识是通过同学们独立学习、合作学习学会的，希望同学们今后能更好地掌握这种学习方法，学好数学，掌握更多的文化知识，为祖国的繁荣富强贡献自己的一份力量。 13、只要同学们善于动脑筋，敢于创新，也完全有可能利用这个特性来进行一些小发明，小创造，快行动起来吧!成功总是青睐于那些善于思考的头脑。我相信，用你们的聪明和智慧一定会获得成功！ 14、同学们在这节课的学习中，你自己运用了哪些学习方法，学到了哪些知识？有哪些收获？大家自己要学会总结，学会回顾，同学们自己想一想，一起来总结一下。 15、同学们通过操作实验推导出了圆锥体的计算公式，我们学的好多知识都是前人经过无数次实验总结出来的，老师希望你们像科学家们那样，在今后的学习活动中不断探索、不断创新、不断实验，就一定能获取更
沪教版2020年八年级下学期英语期末考试试卷A卷 一、单项填空 (共10题；共20分) 1. （2分）I usually watch _______ film at night. A . a;/ B . /;a C . /;/ D . a; a 2. （2分）Mo Yan is my favorite ________. I like his novels a lot. A . teacher B . writer C . driver 3. （2分）—I'm late for your party an accident. I'm sorry. —It doesn't matter. Enjoy yourself here. A . ahead of B . Instead of C . because of 4. （2分）— How about this camera? — It is too expensive. I can't afford it. A . cheap B . heavy C . dear 5. （2分）— Would you like some coffee? —No, thanks. I drink coffee. A . seldom B . often C . only D . always 6. （2分）The boy is ________ see the teacher because he ________ a mistake. A . afraid of; has
B . afraid to; has made C . afraid to; make D . afraid of; made 7. （2分）Tom failed in the exam again ____ he tried his best. A . if B . unless C . though D . because 8. （2分）—_______ did Cao Xueqin spend on the famous book The Story of the Stone? —Nearly 10 years. That's _______ this book is so classical and famous. A . How long，why B . How much，because C . How long，because D . How much，why 9. （2分）--- Do you know ______? --- For a month. A . how long will she be away B . how long she will be away C . how often will she go there D . how often shewill go there 10. （2分）—__________, are you Mr. Wang? —Yes, I am. A . Fine B . Please C . Excuse me D . OK 二、完型填空 (共1题；共10分) 11. （10分）根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。 Mrs. Smith was looking at the show window of a shop selling shirts. She wanted to buy a 1 for
八年级数学 第十六章 二次根式 第一节 二次根式的概念和性质 二次根式 1． 二次根式的概念: 式子)0(≥a a 叫做二次根式．注意被开方数 只能是正数或O ． 2． 二次根式的性质 ①? ??≤-≥==)0()0(2a a a a a a ； ②)0()(2≥=a a a ③)0,0(≥≥?=b a b a ab ； ④)0,0(>≥=b a b a b a 最简二次根式与同类二次根式 1. 被开方数所含因数是整数，因式是整式，不含能开得尽方的因数或因式的二次根式，叫做最简二次根式． 2.化成最简二次根式后，被开方数相同的二次根式，叫做同类二次根式 二次根式的运算 1.二次根式的加减:先把各个二次根式化成最简二次根式，再把同类三次根式分别合并． 2.二次根式的乘法:等于各个因式的被开方数的积的算术平方根， 即 ).0,0(≥≥=?b a ab b a
3.二次根式的和相乘，可参照多项式的乘法进行． 两个含有二次根式的代数式相乘，如果它们的积不含有二次根式，那么这两个三次根式互为有理化因式． 4.二次根式相除，通常先写成分式的形式，然后分子、分母都乘以分母的有理化因式，把分母的根号化去(或分子、分母约分)．把分母的根号化去，叫做分母有理化． 二次根式的运算法则： c c c≥0) ?b a b a ab = ≥ ).0 ,0 (≥ a a =a≥0,b>0） b b =( a≥0) ()n n a a
第十七章 一元二次方程 一元二次方程的概念 1．只含有一个未知数，且未知数的最高次数是2的整式方程叫做一元二次方程 2．一般形式y=ax 2+bx+c （a ≠0），称为一元二次方程的一般式，ax 叫做二次项,a 是二次项系数；bx 叫做一次项，b 是一次项系数；c 叫做常数项 一元二次方程的解法 1．特殊的一元二次方程的解法：开平方法，分解因式法 2．一般的一元二次方程的解法：配方法、求根公式法 3．求根公式24b b ac x -±-=：221244b b ac b b ac x x -+----= , = ； △=24b ac -≥0 一元二次方程的判别式 1．一元二次方程20(0)ax bx c a ++=≠： △＞0时，方程有两个不相等的实数根 △＝0时，方程有两个相等的实数根 △＜0时，方程没有实数根 2．反过来说也是成立的 一元二次方程的应用 1．一般来说，如果二次三项式2ax bx c ++（0a ≠）通过因式分解得2ax bx c ++=12()()a x x x x --；1x 、2x 是一元二次方程20(0)ax bx c a ++=≠的
二年级单词 friend long slide swing seesaw box desk 朋友长得滑梯秋千跷跷板盒子课桌 chair car bear doll table meat grass 椅子小汽车熊玩具娃娃桌子肉草 flower tree boy girl 花树男孩女孩 时间：morning afternoon evening night 早上，上午下午傍晚夜晚 数字：one two three four five six seven eight nine ten 1 2 3 4 5 6 7 8 9 10 形容词：big small thin fat tall 大的小的瘦的胖的高的 short long young old 矮的；短的长的年轻的年老的 家庭成员：sister brother mother father 姐妹兄弟妈妈爸爸 grandfather grandmother 爷爷（外公）奶奶（外婆）
身体器官： hair head face eye mouth nose ear hand 头发头脸眼睛嘴巴鼻子耳朵手 文具：pencil pencil case book rubber ruler bag 铅笔铅笔盒书橡皮尺子书包动词：run write swim fly draw sing dance 跑写游泳飞画画唱歌跳舞 skip ride a bicycle 跳绳骑自行车 颜色：yellow red green blue orange 黄色的红色的绿色的蓝色的橘色的 动物：fox hippo monkey lion tiger 狐狸河马猴子狮子老虎 elephant rabbit panda dog cat 大象兔子熊猫狗猫 餐具：bowl plate spoon chopsticks 碗盘子勺子筷子 自然物质：sun moon star sky 太阳月亮星星天空
沪教牛津版小学英语二年级下册(2b)教学 计划
民办红扬小学二年级英语下册教学计划 （2012—2013年度第二学期） 一、全册教材简析： 本册书共九单元，每单元的话题为：Unit1 Farm animal ; Unit2 In the circus ; Unit 3 My room ; Unit 4 In the park ; Unit5 wash with water ; Unit 6 Eating and drinking ; Unit 7 Hot summer ; Unit 8 Time. 最后一单元是复习单元，每一单元分Let’s act. Let’s talk. Let’s 六个版块。整本书教学内容与 learn . Letters. Let’s play. Let’s enjoy 学生生活紧密联系，围绕“动物，房间，运动,水，饮食，夏天，时 间表达”几个话题，学习简单的交际用语。每一单元穿插字母音和形 的学习。 二、学期教学总目标： 1激发小朋友学习英语的兴趣，培养他们学习英语的积极态 度，并具有一定的语音、语调，及良好的学习习惯和英语交际的能 力，为以后学习打下良好的基础。 中的句子,并能根据指令作出动作反2能听懂、理解Let’s act. 应。 3能说Let’s talk中的句子,能在情景中进行简单的交流。 4能认读Let’s learn中的单词。 5 能做一些英语小游戏。 6 能唱Let’s enjoy中的歌谣和小诗,理解小故事。
7 26个字母的大小写认读。 三、本册教材重、难点： 单词,句重点：1、每一单元中的Let’s talk. Let’s learn . Letters 子。 2、通过真实、自然地情景教学9组会话，并进行简单的 交流。 难点：1 能将所学的知识点运用到实际情景中去。 2．学习持久性和良好的学习习惯的培养。 四、教学内容及进程安排 中的六个动物的单 1、Unit1 Farm animal 能认读Let’s learn 词；会说、认读let’s talk部分和let’s learn 中的单词和句子；能听 懂Let’s act, Let’s play 中的句子并作出反应；理解并表演let’s 六个动物单enjoy部分的故事；字母: N n, O o的认读；Let’s learn 词音和形；听懂、会说let’s talk中的会话；单词的读音和认识；对 话在实际情景中的应用。 2、Unit2 In the circus 继续学习动物名称, 能认读Let’s learn 中的六个动物的单词；会说、认读let’s talk部分和let’s learn 中的 中的句子并作出反应；理 单词和句子；能听懂Let’s act, Let’s play 解并会唱let’s enjoy部分的歌曲；字母Pp,Qq的认读；Let’s learn 六个动物单词音和形；听懂、会说let’s talk中的会话： a、Elephant的发音, b、在实际情境中运用对话。
平行四边形 【定义】两组对边分别平行的四边形叫做平行四边形。 【性质】 1.根据定义得，平行四边形的两组对边分别平行 2.平行四边形的对边相等 3.平行四边形的对角相等 4.夹在两条平行线间的平行线段相等 5.平行四边形的两条对角线相互平分 6.平行四边形是中心对称图形，对称中心是两条对角线的交点【平行四边形的判定】 1.根据定义来判定 2.两组对边分别相等的四边形是平行四边形 3.一组对边平行且相等的四边形是平行四边形 4.对角线相互平分的四边形是平行四边形 5.两组对角分别相等的四边形是平行四边形 矩形 【定义】有一个内角是直角的平行四边形叫做矩形 【性质】 1.矩形的四个角都是直角 2.矩形的两条对角线相等 3.矩形是中心对称图形，也是轴对称图形 【判定】 1.根据定义来判定 2.有三个内角是直角的四边形是矩形 3.对角线相等的平行四边形是矩形 菱形 【定义】有一组邻边相等的平行四边形叫做菱形 【性质】 1.菱形的四条边都相等 2.菱形的对角线相互垂直，并且每一条对角线平分一组对角 3.菱形是中心对称图形，也是轴对称图形 4.菱形的面积等于两条对角线长的乘积的一半 【判定】 1.根据定义来判定 2.四条边都相等的四边形是菱形 3.对角线相互垂直的平行四边形是菱形
正方形（是特殊的矩形，亦为特殊的菱形——具备两者所有的性质） 【定义】有一组邻边相等并且有一个内角是直角的平行四边形叫做正方形。 【性质】 1.正方形的四个角都是直角，四条边都相等 2.正方形的两条对角线相等，并且互相垂直，每条对角线平分一组对角 【判定】 1.根据定义来判定 2.有一组邻边相等的矩形是正方形 3.有一个内角是直角的菱形是正方形 梯形 【定义】一组对边平行而另一组对边不平行的四边形叫做梯形。特别地，有一个角是直角的梯形叫做直角梯形，两腰相等的梯形叫做等腰梯形。 【等腰梯形的性质】 1.等腰梯形在同一底上的两个内角相等 2.等腰梯形的两条对角线相等 【等腰梯形的判定】 1.在同一底上的两个内角相等的梯形是等腰梯形 2.对角线相等的梯形是等腰梯形 三角形、梯形的中位线 【定义】联结三角形两边的中点的线段叫做三角形的中位线；联结梯形两腰的中点的线段叫做梯形的中位线。 【性质】 1.三角形的中位线平行于第三边，并且等于第三边的一半 2.梯形的中位线平行于两底，并且等于两底和的一半
八年级下学期复习提纲 第七章力与运动 第一节科学探究：牛顿第一定律第二节力的合成第三节力的平衡 一、惯性和惯性定律： 1、伽利略斜面实验： ⑴三次实验小车都从斜面顶端滑下的目的是：保证小车开始沿着平面运动的速度相同。 ⑵实验得出得结论：在同样条件下，平面越光滑，小车前进地越远。 ⑶伽利略的推论是：在理想情况下，如果表面绝对光滑，物体将以恒定不变的速度永远运动下去。 ⑷伽科略斜面实验的卓越之处不是实验本身，而是实验所使用的独特方法——在实验的基础上，进行理想化推理。（也称作理想化实验）它标志着物理学的真正开端。 2、牛顿第一定律： ⑴牛顿总结了伽利略、笛卡儿等人的研究成果，得出了牛顿第一定律，其内容是：一切物体在没有受到力的作用的时候，总保持静止状态或匀速直线运动状态。 ⑵说明： A、牛顿第一定律是在大量经验事实的基础上，通过进一步推理而概括出来的，且经受住了实践的检验所以已成为大家公认的力学基本定律之一。但是我们周围不受力是不可能的，因此不可能用实验来直接证明牛顿第一定律。 B、牛顿第一定律的内涵：物体不受力，原来静止的物体将保持静止状态,原来运动的物体,不管原来做什么运动,物体都将做匀速直线运动. C、牛顿第一定律告诉我们:物体做匀速直线运动可以不需要力，即力与运动状态无关，所以力不是产生或维持运动的原因。 3、惯性： ⑴定义：物体保持运动状态不变的性质叫惯性。 ⑵说明：惯性是物体的一种属性。一切物体在任何情况下都有惯性，惯性大小只与物体的质量有关，与物体是否受力、受力大小、是否运动、运动速度等皆无关。 4、惯性与惯性定律的区别： A、惯性是物体本身的一种属性，而惯性定律是物体不受力时遵循的运动规律。 B、任何物体在任何情况下都有惯性，（即不管物体受不受力、受平衡力还是非平衡力），物体受非平衡力时，惯性表现为“阻碍”运动状态的变化；惯性定律成立是有条件的。 ☆人们有时要利用惯性，有时要防止惯性带来的危害，请就以上两点各举两例（不要求解释）。答：利用：跳远运动员的助跑；用力可以将石头甩出很远；骑自行车蹬几下后可以让它滑行。防止：小型客车前排乘客要系安全带；车辆行使要保持距离；包装玻璃制品要垫上很厚的泡沫塑料。二、力的合成： ⑴合力的概念：一个力产生的效果根两个力共同产生的效果相同这个力叫做那两个力的合力。 ⑵二力合成定义：求两个力合力 ⑶同一直线上二力合成规律： 若两个力方向相同，则合力大小等于这两个力的大小之和方向跟两个力的方向相同。 若两个力方向相反，则合力大小等于这两个力的大小之差方向跟较大的那个力方向相同口诀：同向相加，异向相减，方向随大⑷在物理学中，我们研究某物体或物理现象的作用效果时，经常把作用效果相同的两种或两种以上的物理现象在不同的物理环境下相互替代．这种研究问题的方法给问题的阐释或解答带来极大方便，我们称这种研究问题的方法为等效替代法。 除定义合力时用等效替代法，电学中，定义串联总电阻和并联总电阻都运用了等效替代法。 练习：☆分析课本（P122）图8-19，图8-20看他们有什么共同现象，能共同反映出那些物理知识。（至少写出三点） 共同现象：失去支持后最终都会向地面降落。 共同反映的物理知识：①地面附近的物体都受到重力的作用。②重力的方向总是方向竖直向下的。 ③力可以改变物体的运动状态。④重力势能可以转化为动能。 ☆假如失去重力将会出现的现象：（只要求写出两种生活中可能发生的） ①抛出去的物体不会下落；②水不会由高处向低处流③大气不会产生压强； 三、二力平衡： 1、定义：物体在受到两个力的作用时，如果能保持静止状态或匀速直线运动状态称二力平衡。 2、二力平衡条件：二力作用在同一物体上、大小相等、方向相反、两个力在一条直线上 概括：二力平衡条件用四字概括“一、等、反、一”。 3、平衡力与相互作用力比较： 相同点：①大小相等②方向相反③作用在一条直线上不同点：平衡力作用在一个物体上可以是不同性质的力；相互力作用在不同物体上是相同性质的力。 画图时注意：①先画重力然后看物体与那些物体接触，就可能受到这些物体的作用力②画图时还要考虑物体运动状态。 第八章 压强 第一节压强第二节科学探究液体的压强第三节空气的“力量”第四节流体压强与流速的关系 一、固体的压力和压强 1、压力： ⑴定义：垂直压在物体表面上的力叫压力。 ⑵压力并不都是由重力引起的，通常把物体放在桌面上时，如果物体不受其他力，则压力F = 物体的重力G ⑶固体可以大小方向不变地传递压力。 ⑷重为G