八年级下册电子书
2020最新人教版八年级道德与法治下册(部编版五·四学制)电子课本课件【全册】
第一单元 坚持宪法至上
2020最新人教版八年级道德与法治 下册(部编版五·四学制)电子课本课
件【全册】
2020最新人教版八年级道德与法 治下册(部编版五·四学制)电子课
本课件【全册】目录
0002页 0004页 0041页 0078页 0145页 0197页 0256页 0278页 0322页 0407页 0479页 0511页 0538页 0612页 0641页 0711页
第一单元坚持宪法至上 公民权利的保障书 第二课 保障宪法实施 加强宪法监督 第三课 公民权利 依法行使权利 公民基本义务 第三单元 人民当家作主 基本经济制度 基本政治制度 国家权力机关 国家行政机关 国家司法机关 第七课 尊重自由平等 自由平等的追求 公平正义的价值
八年级下册闽教版英语书电子课本
八年级下册闽教版英语书电子课本Unit 1 What’s the matter?Unit 2 I’ll help to clean up the city parks.Unit 3 Could you please clean your room?Unit 4 Why don’t you talk to your parents?Unit 5 What were you doing when the rainstorm came?Unit 6 An old man tried to move the mountains.Unit 7 What’s the highest mountain in the world?Unit 8 Have you read Treasure Island yet?Unit 9 Have you ever been to a museum?Unit 10 I’ve had this bike for three years.Notes on the TextTape scriptsGrammar八年级下英语课文原文(一)P3 3aBus Driver and Passengers Save an Old ManAt 9:00 a.m. yesterday, bus No. 26 was going along Zhonghua Road when the driver saw an old man lying on the side of the road. A woman was next to him, shouting for help.The bus driver, 24-year-old Wang Ping, stopped the bus without thinking twice. He got off and asked the woman what happened. Shesaid that the man had a heart problem and should go to the hospital. Mr. Wang knew he had to act quickly. He told the passengers that he must take the man to the hospital. He expected most or all of the passengers to get off and wait for the next bus.But to his surprise, they all agreed to go with him. Some passengers helped Mr. Wang to move the man ona the bus.Thanks to Mr. Wang and the passengers, the doctors saved the man in time. "It's sad that many people don't want to help others because they don‟t want any trouble," says one passenger. "But the driver didn't think about himself. He only thought about saving a life."八年级下英语课文原文(二)P6 2bHe Lost His Arm But Is Still ClimbingAron Ralston is an American man who is interested in mountain climbing. As a mountain climber, Aron is used to taking risks. This is one of the exciting things about doing dangerous sports. There were many times when Aron almost lost his life because of accidents. On April 26, 2003, he found himself in a very dangerous situation when climbing in UtahOn that day, Aron's arm was caught under a 2,000-kilo rock that fell on him when he was climbing by himself in the mountains. Because he could not free his arm, he stayed there for five days and hoped thatsomeone would find him. But when his water ran out, he knew that he would have to do something to save his own life. He was not ready to die that day. So he used his knife to cut off half his right arm. Then, with his left arm, he bandaged himself so that he would not lose too much blood. After that, he climbed down the mountain to find help.After losing his arm, he wrote a book called Between a Rock and a Hard Place. This means being in a difficult situation that you cannot seem to get out of. In this book, Aron tells of the importance of making good decisions, and of being in control of one's life. His lose for mountain climbing is so great that he kept on climbing mountains even after this experience.Do we have the same spirit as Aron? Let's think about it before we find ourselves “between a rock and a hard place”, and before we have to make a decision that could mean life or death.八年级下英语课文原文(三)P11 3aStudents Who VolunteerMario Green and Mary Brown from Riverside High School give up several hours each week to help others.Mario loves animals and wants to be an animal doctor. He volunteers at an animal hospital every Saturday morning. Mario believes it can help him to get his future dream job. “It' s hard work , ”he says ,“but I want to learn more about how to care for animals . I get such a strong feeling of satisfaction when I see the animals get better and the look of joy on their owners' faces.”Mary is a book lover. She could read by herself at the age of four. Last year she decided to try out for a volunteer after-school reading program .she still works there once a week to help kids learn to read. The kids are sitting in the library, but you can see in their eyes that they‟re going on a different journey with each new book. Volunteering here is a dream come true for me. I can do what I love to do and help others at the same time.。
冀教版八下语文课本电子版
冀教版八下语文课本电子版一个白胡子穷老头儿向我们乞求施舍。
我的同伴约瑟夫·达弗朗舍竟给了他一个五法郎的银币。
我觉得有点惊奇。
他于是对我说：这个可怜的人使我想起一段往事，这段往事我一直念念不能忘怀。
下面我就来讲给您听。
我的家庭原籍勒阿弗尔，并不是有钱人家，也就是勉强度日罢了。
我的父亲做事，很晚才从办公室回来，挣的钱不多。
我有两个姐姐。
我的母亲对我们的拮据生活感到非常痛苦，她常常找出一些尖酸刻薄的话，一些含蓄、恶毒的责备话发泄在我的父亲身上。
这个可怜人这时候总做出一个手势，叫我看了心里十分难过。
他总是张开了手摸一下额头，好像要抹去根本不存在的汗珠，并且总是一句话也不回答。
我体会到他那种无可奈何的痛苦。
那时家里样样都要节省;有人请吃饭是从来不敢答应的，以免回请;买日用品也是常常买减价的日用品和店铺里铺底的存货。
姐姐们自己做衣服，买十五个铜子一米的花边时还常常要在价钱上争论半天。
我们日常吃的是肉汤和用各种方式做的牛肉。
据说这又卫生又富于营养，不过我还是喜欢吃别的东西。
我要是丢了钮子或是撕破了裤子，那就要狠狠地挨一顿骂。
可是每星期日我们都要衣冠整齐地到防波堤上去散步。
我的父亲穿着礼服，戴着礼帽，套着手套，让我母亲挽着胳膊;我的母亲打扮得五颜六色，好像节日悬万国旗的海船。
姐姐们总是最先打扮整齐，等待着出发的命令;可是到了最后一刻，总会在一家之主的礼服上发现一块忘记擦掉的污迹，于是赶快用旧布蘸了汽油来把它擦掉。
于是我的父亲头上依旧顶着大礼帽，只穿着背心，露着两只衬衫袖管，等着这道手续做完;在这时候，我的母亲架上她的近视眼镜，脱下了手套，免得弄脏它，忙得个不亦乐乎。
全家很隆重地上路了。
姐姐们挽着胳膊走在最前面。
她们已经到了出嫁的年龄，所以常带她们出来叫城里人看看。
我依在我母亲的左边，我父亲在她的右首。
我现在还记得我可怜的双亲在星期日散步时候那种正言厉色、举止庄重、郑重其事的神气。
他们挺直了腰，伸直了腿，迈着沉着的步伐向前走着，就仿佛他们的态度举止关系着一桩极端重要的大事。
八年级下册语文古诗2021电子书
八年级（下）古诗文背诵篇目关雎《诗经·周南》关关雎鸠，在河之洲。
窈窕淑女，君子好逑。
参差荇菜，左右流之。
窈窕淑女，寤寐求之。
求之不得，寤寐思服。
悠哉悠哉，辗转反侧。
参差荇菜，左右采之。
窈窕淑女，琴瑟友之。
参差荇菜，左右芼之。
窈窕淑女，钟鼓乐之。
蒹葭《诗经·秦风》蒹葭苍苍，白露为霜。
所谓伊人，在水一方。
溯洄从之，道阻且长。
溯游从之，宛在水中央。
蒹葭萋萋，白露未晞。
所谓伊人，在水之湄。
溯洄从之，道阻且跻。
溯游从之，宛在水中坻。
蒹葭采采，白露未已。
所谓伊人，在水之涘。
溯洄从之，道阻且右。
溯游从之，宛在水中沚。
式微《诗经·邶风》式微式微，胡不归？微君之故，胡为乎中露？式微式微，胡不归？微君之躬，胡为乎泥中？子衿《诗经·郑风》青青子衿，悠悠我心。
纵我不往，子宁不嗣音？青青子佩，悠悠我思。
纵我不往，子宁不来？挑兮达兮，在城阙兮。
一日不见，如三月兮！送友人唐·李白青山横北郭，白水绕东城。
此地一为别，孤蓬万里征。
浮云游子意，落日故人情。
挥手自兹去，萧萧班马鸣。
送杜少府之任蜀州唐·王勃城阙辅三秦，风烟望五津。
与君离别意，同是宦游人。
海内存知己，天涯若比邻。
无为在歧路，儿女共沾巾。
望洞庭湖赠张丞相唐·孟浩然八月湖水平，涵虚混太清。
气蒸云梦泽,波撼岳阳城。
欲济无舟楫，端居耻圣明。
坐观垂钓者，徒有羡鱼情。
题破山寺后禅院唐·常建清晨入古寺，初日照高林。
曲径通幽处，禅房花木深。
山光悦鸟性，潭影空人心。
万籁此都寂，但余钟磬音。
卜算子·黄州定慧院寓居作宋·苏轼缺月挂疏桐，漏断人初静。
时见幽人独往来，缥缈孤鸿影。
惊起却回头，有恨无人省。
拣尽寒枝不肯栖，寂寞沙洲冷。
卜算子·咏梅宋·陆游驿外断桥边，寂寞开无主。
已是黄昏独自愁，更著风和雨。
无意苦争春，一任群芳妒。
零落成泥辗作尘，只有香如故。
桃花源记晋·陶渊明晋太元中，武陵人捕鱼为业。
2023八年级下册语文书人教版电子书
2023八年级下册语文书人教版电子书1. 介绍《2023八年级下册语文书人教版电子书》是为了方便学生和教师使用而开发的电子书。
该电子书是基于人教版八年级下册语文课程的教材内容，旨在提供学生快速、便捷的学习方式。
本文档将详细介绍《2023八年级下册语文书人教版电子书》的特点、功能以及使用方法。
2. 特点2.1 多媒体交互《2023八年级下册语文书人教版电子书》采用了多媒体交互的形式，为学生带来更加生动、直观的学习体验。
通过视频、音频等多媒体内容的呈现，可以帮助学生更好地理解课文内容。
同时，学生还可以通过电子书提供的互动模块参与练习和测试，增强学习效果。
2.2 个性化学习电子书提供了个性化学习的功能。
学生可以根据自己的学习进度和需求，自由选择学习的内容和顺序。
同时，电子书还根据学生的学习记录和表现，智能推荐相关的习题和辅助资源，帮助学生更好地提高学习效果。
2.3 跨平台使用《2023八年级下册语文书人教版电子书》支持跨平台使用。
学生可以在电脑、平板和手机等多种设备上使用该电子书，随时随地进行学习。
无论是在学校、家中还是在外出时，学生都可以方便地查阅课文、完成作业等。
3. 功能3.1 课文阅读电子书提供了八年级下册语文课本的完整内容，学生可以通过电子书快速浏览和阅读课文。
课文的呈现形式可根据学生的需要进行调整，支持横向和竖向阅读。
3.2 多媒体播放为了加深学生对课文内容的理解和记忆，电子书提供了音频和视频的播放功能。
学生可以直接在电子书中播放与课文内容相关的音频和视频资料，提高学习效果。
3.3 互动练习与测试电子书还提供了丰富的互动练习和测试题目，帮助学生巩固所学知识。
学生可以在电子书上完成练习和测试，并实时获得答案和解析，及时发现和纠正错误。
3.4 笔记和标注学生可以在电子书上进行笔记和标注。
比如，可以在重点句子或段落上进行标记，方便之后的复习和回顾。
同时，学生还可以添加自己的笔记，记录对课文内容的理解和思考。
北师大版八年级下册物理电子书第78页学子斋
北师大版八年级下册物理电子书第78页学子斋1.力是一个物体对另一个物体的作用。
力不能脱离物体单独存在；施加力的物体叫施力物体，受到力的物体叫受力物体，其中被研究的对象都是受力物体。
2.力产生的条件：①必须有两个或两个以上的物体。
②物体间必须有相互作用（可以不接触）。
3.力学必记的三句话：①物体间力的作用是相互的（一个物体是施力物体的同时也是受力物体）②力可以改变物体的运动状态（动←→静、快←→慢、方向改变）③力可以使物体发生形变。
（不能说改变形变或物体形变发生改变）4.力的三要素：大小、方向、作用点。
（它们都可以影响力的作用效果）5.力（F）：国际单位是牛（顿），符号是N；2个鸡蛋在手上对手的力大约是1N。
6.力的表示法有2种：用一个带有箭头的线段表示力，线段的长度表示力的大小，箭头表示力的方向，起点（或终点）表示力的作用点（同光线一样，这个方法叫理想模型法）7.口诀为：一定点二画线、三定比例四截线、五在末端标尖尖、六是力的大小写尖边。
注：①力的示意图比力的图示少了画标度的过程。
可以这样记：示意图就是意思意思，只是表示出大致的意思就可以了，没有图示详细；②在同一个图中，如果有几个力的话要公用一个标度和力的作用点。
（作用点一定在受力物体上，而且一般取中心。
）③线段长度没有半格的，也没有一个格的，也就是说最少2个格，且是格的整数倍。
8.物体在撤去外力后能恢复到原来的形状叫弹性形变。
产生条件或依据：①物体间是否直接；②接触处是否有相互挤压和拉伸。
9.弹力的大小：F=k x 其中F：弹力；k：劲度系数，和物体本身有关；x：形变量，即形变后的长度也原长的差。
即弹力的大小与物体本身额弹性强弱和形变量的大小有关。
形变量越大，弹力越大，弹簧测力计就是根据这个原理制成的：在一定范围内，弹簧的伸长量与拉力成正比。
10.弹力的方向：与受力物体形变方向相反；常见的弹力有压力、拉力和支持力。
11.弹簧测力计又叫弹簧秤，可测重力和拉力。
(完整版)英语八年级下册课文电子版
2014外研版初中八年级英语下册课文电子版Module 1 Feelings and impressionsUnit 1 It smells delicious.Tony: Mm…What a delicious smell! Your pizza looks so nice.Betty: Thanks! Would you like to try some?Tony: Yes, please. It looks lovely, it smells delicious, and mm, it tastes good.that on top?Daming: What’ｓBetty: Oh, that’ｓcheese. Do you want to try a piece?smell fresh. It smells too strong and it tastes Daming: Ugh! No, thanks. I’ｍafraid I don’ｔlike cheese. It doesn’ｔa bit sour.Betty: Well, my chocolate cookies are done now. Have a try!Daming: Thanks! They taste really sweet and they feel soft in the middle.Tony: Are you cooking lots of different things? You look very busy!some pizza and some cookies, and now I’ｍmaking an apple pie.Betty: Yes, I am! There’ｓDaming: Apple pie sounds nice. I have a sweet tooth, you know. Shall I get the sugar?sugar? Taste it first. It might be salt.Betty: Yes, please. Oh, are you sure that’ｓthis? It tastes sweet too.Daming: No, it’ｓsugar. Tony: What’ｓOK. It tastes sweet. It’ｓstrawberry jam, for the cake.Betty: That’ｓmy lucky day!Daming: Good, everything tastes so sweet! It’ｓQuestions:pizza taste good?1. Does Tony’ｓ_______________________________________________________________________________ Daming like the cheese?2. Why doesn’ｔ_______________________________________________________________________________3. What’ｓBetty doing?_______________________________________________________________________________4. Who has a sweet tooth?_______________________________________________________________________________Keys:1. Yes, it does.smell fresh. It smells too strong and it tastes a bit sour.2. Because it doesn’ｔ3. She is making an apple pie.4. Daming.Unit 2 I feel nervous when I speak ChineseFROM: SallyTO: LinglingSUBJECT: Re : Welcome to ChinaHi Lingling,wait to meet you.1. Thanks for your last message, It was great to hear from you, and I can’ｔ2. I hope you will know me from my photo when I arrive at the airport. I’ｍquite tall, with short fair hair, and Iwear glasses. I’ll wear jeans and a T-shirt for the journey, but I’ll also carry my warm coat. I’ve got your photo ---- you look very pretty, so I’ｍsure we’ll find each other!3. Thanks for telling me about your hobbies. You sound just like me! I spend a lot of time playing classical musicwith my friends at school, but I also like dance music – I love dancing! I enjoy sports as well, especially tennis.good at everything, but I’ｍnot.My brother is in the school tennis team –I’m very proud of him! He’ｓSometimes I get bad marks at school, and I feel sad. I should work harder.4. You asked me, “How do you feel about coming to China?” Well, I often feel a bit sad at first when I leave mymum and dad for a few days, and I’m quite shy when I’m with strangers. I feel nervous when I speak Chinese, but I’ll be fine in a few days. I’m always sorry when I don’ｔknow how to do things in the right way, so pleasetell you how excited I am about help me when I’ｍwith you in China! Oh, I’ｍ afraid of flying. But I can’ｔgoing to China!See you next week!Love,SallyQuestions:1. What does Sally look like?_______________________________________________________________________________hobbies?2. What are Sally’ｓ_______________________________________________________________________________3. Does Sally usually get bad marks?_______________________________________________________________________________4. How does Sally feel about coming to China?_______________________________________________________________________________5. How does Sally feel when she is going to China?_______________________________________________________________________________Keys:quite tall, with short fair hair, and she wears glasses.1. She’ｓ2. Playing classical music, dance music and tennis.3. No, she doesn’t.4. She often feels a bit sad at first when she leaves her mum and dad for a few days.5. Exciting.Module 2 ExperiencesUnit 1 I’ve also entered lots of speaking competitionsTony: Hi, Lingling. What are you doing?Lingling: I’ｍentering a competition.Tony: What kind of competition?Lingling: A speaking competition.Tony: Great. It’ll help you improve your speaking. And maybe you will win a prize.Lingling: The first prize is “My dream holiday”.Tony: Have you ever won any prizes before?Lingling: No, I haven’t.I’ve always wanted to go on a dream holiday. But I can’ｔafford it. The plane tickets are too expensive.also entered lots of speaking competitions, but haven’ｔwon any prizes. I’ve stopped Tony: Well, good luck! I’vetrying now.a writing competition. Around the World in 80 Days. To win it, you need to write a short Lingling: Look! Here’ｓstory about a place you’ve visited.Tony: That sounds wonderful, but I’ve never travelled a lot. How can I write about it?need to be true! You can make it up.worry. It doesn’ｔLingling: Don’ｔinteresting, I’ll try. I hope I will win, then I will invite you to come with me.Tony: That’ｓLingling: Sorry! The first prize is only the book called Around the World in 80 Day!Questions:1. What kind of competition does Lingling enter?_______________________________________________________________________________ the first prize of the speaking composition?2. Wh at’ｓ_______________________________________________________________________________ Lingling go on a dream holiday?3. Why doesn’ｔ_______________________________________________________________________________4. Has Tony entered lots of speaking competitions?_______________________________________________________________________________Keys:1. A speaking competition.2. The first prize is “My dream holiday”.3. She can’t afford it. The plane tickets are too expensive.4. Yes, he has.Unit 2 They have seen the Pyramids.Mike Robinson is a fifteen–year-old American boy and his sister Clare is fourteen. At the moment, Mike and Clare are in Cairo in Egypt, one of the biggest and busiest cites in Africa.They moved here with their parents two years ago. Their father, Peter, works for a very big company. The company has offices in many countries, and it has sent Peter to work in Germany, France and China before. Peter usually stays in a country for about two years. Then the company moves him again. His family always goes with him.The Robinsons love seeing the world. They have been to many interesting places. For example, in Egypt,they have seen the Pyramids, travelled on a boat on the Nile River, and visited the palaces and towers of ancient kings and queens.Mike and Clare have also begun to learn the language of the country, Arabic. This language is different from English in many ways, and they find it hard to spell and pronounce the words. However, they still enjoy learningit. So far they have learnt to speak German, French, Chinese and Arabic. Sometimes they mix the languages. “It’s really fun,” said Clare.The Robinsons are moving again. The company has asked Peter to work back in the US. Mike and Clare are happy about this. They have friends all over the world, but they also miss their friends in the US. They are counting down the days.Questions:1. How long have the Robinsons been in Egypt?_______________________________________________________________________________2. Why do they live in Cairo?_______________________________________________________________________________3. What have they seen and done in Egypt?_______________________________________________________________________________4. What do Mike and Clare find difficult about Arabic?_______________________________________________________________________________5. Are they looking forward to going home?_______________________________________________________________________________Keys:1. Two years2. Their father, Peter, works in Cairo.3. In Egypt, they have seen the Pyramids, travelled on a boat on the Nile River, and visited the palaces and towersof ancient kings and queens.4. This language is different from English in many ways, and they find it hard to spell and pronounce the words.5. Yes, they are.Module 3 Journey to spaceUnit 1 Has it arrived yet ?Daming: Hi, Tony. What are you up to?just made a model spaceship for our school project.Tony: Hi, Daming. I’vestarted yet, because I’ｍnot sure how to make it. Can you help me?Daming: I haven’ｔTony: Sure, no problem. Have you heard the lasted news? Scientists have sent a spaceship to Mars. The journey has taken several months. Daming: Has it arrived yet?why it’ｓon the news.Tony: Yes, it has arrived already. That’ｓDaming: So have they discovered life on Mars?yet.Tony: No, they haven’ｔDaming: Are there any astronauts in the spaceship?Tony: No, there aren’t.Daming: Why? Astronauts have already been to the moon.Tony: Yes, but no one has been to Mars yet, because Mars is very far away, much farther than the moon. Lots of scientists are working hard in order to send astronauts to Mars one day.interesting! How can I get information on space travel?Daming: That’ｓTony: You can go online to search for the information.Daming: I will. Thank you, Tony!Now answer the questions:1. What school project have Daming and Tony got?_______________________________________________________________________________2. How does Daming feel about the school project?_______________________________________________________________________________3. What news has Tony heard?_______________________________________________________________________________4. Has anyone been to Mars? Why?_______________________________________________________________________________Keys:1. They’ve just made a model spaceship for their school project.2. Daming is not sure how to make it.3. Scientists have sent a spaceship to Mars. The journey has taken several months.4. No one has been to Mars yet, because Mars is very far away, much farther than the moon.Unit 2 We have not found life on any other planets yet.Scientists think that there has been life on earth for hundreds of millions of years. However, we have not found life on any other planets yet.The earth is a planet and it goes around the sun. Seven other planets also go around the sun. None of them has an environment like that of the earth, so scientists do not think they will find life on them. The sun and its planets are called the solar system, and our solar system is a small part of a much larger group of stars and planets, called the Galaxy or the Milky Way. There are billions of stars in the Galaxy, and our sun is only one of them.Scientists have also discovered many other galaxies in the universe. They are very far away and their light has to travel for many years to reach us. So how large is the universe? It is impossible to imagine.Scientists have sent spaceships to the plant of Mars to take photos. They even have sent spaceships to travel outside the solar system. However, no spaceship has travelled far enough to reach near other stars in our Galaxy. Scientists have always asked the question: With so many stars in the universe, are we alone, or is there life out there in space? Have there been visitors to the earth from other planets? Why has no one communicated with us? We do not know the answers…yet.Questions:1. Have we found life on any other planets?___________________________________________________________________________2. How many planets are there going around the sun?______________________________________________________________________________ the scientists think they will find life on the other planets?3. Why don’ｔ______________________________________________________________________________ the Milky Way?4. What’ｓ______________________________________________________________________________Keys:1. No, we haven’t.2. Eight.3. None of them has an environment like that of the earth, so scientists do not think they will find life on them.4. The sun and its planets are called the solar system, and our solar system is a small part of a much larger groupof stars and planets, called the Galaxy or the Milky Way.Module 4 Seeing the doctordone much exercise since I got my computer.Unit 1 I haven’ｔDoctor: How can I help you?Daming: I feel ill. I’ve got a stomachache and my head hurts.Doctor: How long have you been like this?Daming: Since Friday. I’ve been ill for about three days!Doctor: I see. Have you caught a cold?Daming: I don’ｔthink so.no fever. What kind of food do you eat?Doctor: Let me take your temperat ure…Mm,there’ｓDaming: Usually fast food.Doctor: Do you have breakfast?Daming: No, not usually.why you’ve got a stomachache.the problem! Fast food and no breakfast. That’ｓDoctor: That’ｓDaming: What about the headache?Doctor: Do you do any exercise?done much exercise since I got my computer last year.Daming: Not really. I haven’ｔDcotor: You spend too much time in front of the computer. It can be very harmful to your health.Daming: OK, so what should I do?not serious. First, stop eating fast food and have breakfast every day. Second, get worry. It’ｓDoctor: Well, don’ｔsome exercise, such as running. And I’ll give you some medicine. Take it three times a day.Daming: Thank you, doctor.Questions：1. What has Daming got?_______________________________________________________________________________2. Does Daming have breakfast?_______________________________________________________________________________3. Why has Daming got a stomachache?_______________________________________________________________________________4. Does Daming do any exercise? Why?_______________________________________________________________________________Keys:1. He’ｓgot a stomachache and his head hurts.2. No, he doesn’ｔ3. Fast food and no breakfast.4. No, he spends too much time in front of the computer.Unit 2 We have played football for a year now.Healthy living1. I was not feeling very well so the doctor checked my heart and said I needed more exercise. I have never beenvery active, and I do not like sports. I have always wanted a pet, so my parents gave me a dog for my birthday.Now I get exercise by taking him for a walk every day. I have had him for three months now and I feel really healthy. ----Anna2. Our teacher decided to start a girl’s football team and I thought, “What a great idea!” I was the first member ofthe team. We have played football for a year now and we all feel very fit. Our teacher is the coach, and she also takes part in the same training with us. She is in excellent condition too. ---- Wang Wei3. For the last few years, I went to work by underground. When I got to work, I always felt very sleepy and I wasnot happy. I bought a bike in January. Science then, it has become part of my life. Now I ride to wok every day.It is my daily exercise. I arrive at work with a smile on my face. ---- Thomas4. I was weak after a long illness, so I wanted to exercise more. Then a friend suggested, “Why don’t we go for arun before school?” So we started running a week ago. But I do not enjoy running, and when I get to school, I feel awful. My legs hurt and I am hot all over. Perhaps I am too weak to do any exercise. What do you think?----RichardQuestions:1. What does Anna’ｓfeel well?doctor say when she doesn’ｔ_______________________________________________________________________________2. How does Anna get exercise?_______________________________________________________________________________3. How long has Wang Wei played football?_______________________________________________________________________________4. How does Thomas go to work now?_______________________________________________________________________________5. Does Richard enjoy running?_______________________________________________________________________________Keys:1. She needs more exercise.2. By taking a dog for a walk every day.3. One year.4. By bike.5. No, he doesn’t.Module 5 Cartoonstime to watch a cartoon.Unit 1 It’ｓtime to watch a cartoon.Tony: Daming, we’ve finished our homework. It’ｓwatch Superman!Daming: Good idea, Tony. Let’ｓmore modern.Tony: We watched Superman yesterday. Why don’ｔwe watch Spiderman? It’ｓstronger than Spiderman. He can fly through the sky and fight bad Daming: I think Superman is better. He’ｓpeople.fly, but he climbs up buildings with his hands and feet. That’ｓcool. I want to be someone Tony: Spiderman can’ｔlike him.a real hero!Daming: Well, Superman is brave. He keeps fighting bad people. That’ｓthink we agree.Tony: I don’ｔwatch Tom and Jerry then.Daming: All right. Let’ｓhelp laughing when I watch them. Tony: Yeah! I like humorous cartoons. Tom and Jerry are very funny. I can’ｔDaming: Yes, Jerry is too smart for Tom.Tony: The cut mouse always beats the cat! They fight a lot, but they really love each other. Sometimes theylesson there!protect each other and work together. I think there’ｓUnit 2 Tintin has been popular for over eighty yearsCartoon heroesNemo is a cute orange-and-white fish and Shrek is an ugly green animal. They look very different, but both of them have won the hearts of young people all over the world. The pictures of these popular cartoon heroes are everywhere, on office desks, handbags, and computer screens.There are also some older cartoon favourites, for example, the Monkey King. He is the hero of a story called Havoc in Heaven. He leads a group of monkeys against the Emperor of Heaven and his guards. He is brave, clever and humorous. Parents and children laugh together as Monkey King makes a terrible mess in heaven. They always expect to see more Monkey King cartoons.Tintin is another favourite cartoon hero. He has been popular for over eighty years, ever since the artistinvented him in 1929. Tintin has red hair and a small white dog. He works for a newpaper and has lots ofstories in more than fifty languages. exciting experiences. Fans have bought about 200 million copies of Tintin’ｓTintin appeared in China in the 1980s. Many Chinese still collect these black-and-white Tintin books.Finally, Snoopy, a cute dog, celebrated his 60th birthday in 2010.Snoopy lives in his own private world and finds real life hard to understand. Charles Schulz created Snoopy and his friends, and drew the cartoons to satisfy older people as well as children.Module 6 HobbiesUnit 1 Do you collect anything?a bit of mess. I’ll put the fans on the Lingling: Hi, everything! Come in and find somewhere to sit down. Sorry, it’ｓshelf.Betty: Let me have a look. You’ve got so many fans.Lingling: Yes, about sixty.Betty: Where did you get them?Lingling: Most of them are presents. People often give me fans as presents because they know I like them. Do you collect anything?Betty: Yes, I collect coins and notes, you know, like British pounds and US dollars and cents.Lingling: Coins? They must be really valuable. Can I see them?Betty: Sure! I’ll show you my stamps too. I’ve collected stamps from all over the world. I’ve got six or seven books of stamps.cost as much as yours — I collect tickets, bus tickets and train tickets!Tony: My hobby doesn’ｔdo anything with old tickets!Betty: You can’ｔTony: I know, but when I look at them, I remember some wonderful places.very important. People usually collect things just to remember something Lingling: Right! Their value isn’ｔimportant in their lives.Questions：1. What does Lingling collect?_______________________________________________________________________________2. How can Lingling get the fans？_______________________________________________________________________________3. What does Betty collect?_______________________________________________________________________________4. Why do people collect things?_______________________________________________________________________________Keys:1. Fans.2. People often give her fans as presents.3. Coins, notes and stamps.4. People usually collect things just to remember something important in their lives.Unit 2 Hobbies can make you grow as a person.hobbiesDavid’ｓMany students have hobbies, such as reading, painting, growing vegetables and looking after animals. Some hobbies are relaxing and others are active. Hobbies can make you grow as a person, develop your interests and help you learn new skills.David Smith is a student, and one of his hobbies is writing. During the summer of 2010, he spent four weeksat a summer camp. As well as the usual activities, such as sailing and climbing, there was a writing class. ― The teacher is a writer, and she asked us to talk about our lives and tell interesting stories. Then she encouraged us to write about our experiences at the camp.Back at school, David wrote a story about the life of a sixteen–year–old boy, and it came out as a book in 2012. Many young people love his book, and as a result, David has become a successful young writer.David has been very lucky because his hobby has brought him pleasure and success, but writing is not his only hobby. He is also interested in many other things. “I like playing volleyball too,” says David. “I spend some of my free time playing volleyball for my school team. Maybe I’ll write about my volleyball team in my future books.”Questions:1. Why do people usually have hobbies?_______________________________________________________________________________2. Is writing a usual activity for a summer camp?_______________________________________________________________________________3. When did David become a successful writer?_________________________________________________________________________________4. How many hobbies does David have?_______________________________________________________ ______________________Keys:1. Some hobbies are relaxing and others are active. Hobbies can make you grow as a person, develop yourinterests and help you learn new skills.2. Yes, it is.3. 20124. Two.Module 7 Summer in Los AngelesUnit 1 Please write to me and send some photos!（Lingling is preparing for her trip to LA）Lingling: Hi, Betty. I’ｍmaking a list of things for my trip. I like to get things ready earlier. Can you help me? Betty: Sure. How can I help?Lingling: Well, it sounds crazy but I don’t know what to take. Betty: You should take notebooks, pens and a dictionary.Lingling: OK. What clothes should I take to LA？Betty: When are you leaving and how long are you going to stay there？Lingling: I’ｍleaving at the end of July and I’ｍgoing to stay there for four weeks.be sunny and hot there.Betty: Shorts are good, or you can wear light trousers. It’llgot any sunglasses. I’ll buy a pair there.Lingling: I haven’ｔa good idea. But remember, many things are more expensive in America. Have you got anyBetty: That’ｓAmerican dollars?Lingling: Yes. Is 200 dollars enough?Betty: If you’ve already paid for the air tickets and for homestay, it should be OK.Lingling: What else?weigh too much. You’ｄbetter ask the travel company about the total weight for all your Betty: You bag mustn’ｔforget to take your passport.bags. Oh, by the way, don’ｔLingling: OK. Thank you.Betty: You’re welcome. You’ll have a great time. Please write to me and send me some photos!Lingling: Yes, I will.Questions:1. Does Lingling know what to take?________________________________________________________________________2. When is Lingling leaving for LA?________________________________________________________________________3. How long is she going to stay there？________________________________________________________________________4. Will LA be sunny and hot there?________________________________________________________________________Keys:1. No, she doesn't.2. At the end of July.3. She is going to stay there for four weeks.4. Yes, it will.Unit 2 Fill out our form and come to learn English in Los AngelesLearn English in Los AngelesCome and learn English in Los Angeles! We can offer you great summer English courses. You will love coming to Los Angeles to learn about American culture and improve your English at the same time.The courses last for four, six or eight weeks. They start at the beginning of July. Our teachers are well trained and have a lot of experience. They teach English classes for four hours a day. You can work in small or large groups and it depends on your personal choice. We provide books and we set tests every week to check your progress. They are also computers and other forms of technology for personal study.As well as learning English, we want you to experience life in the USA. You stay as a guest with an American family and take part in their daily life. You have meals with the family and do some activities with them, too. For many of our students this is the best part of the course. Many families form close friendships with the students and stay in touch with them. Buy if you prefer, of course, we can stay in a hotel.There are many exciting things to do in Los Angeles. We plan activities every day after class. You can choose to take trips to Hollywood, Disneyland or San Francisco, or you can go shopping.You are certain to get the best possible experience of English and life in the US. You must pay for your course at least one month before it starts. Do not wait—fill out our form and come to learn English in Los Angeles.Questions:1. What do you learn about in an English summer course?______________________________________________________________________________2. Why are there weekly tests?______________________________________________________________________________3. How long does the courses last?______________________________________________________________________________4. What can you do after class?______________________________________________________________________________Keys:1. American culture.2. To check the students' progress.3. The courses last for four, six or eight weeks.3. For many of our students this is the best part of the course.4. You can choose to take trips to Hollywood, Disneyland or San Francisco, or you can go shopping.Module 8 Time offUnit 1 I can hardly believe we’re in the city centreLingling: Here we are. Welcome to Beihai Park.Tony:Wow! It’ｓso quiet that I can even hear the birds singing! I can hardly believe we're in the city centre. Lingling: This park is famous for its lake, the bridge and the ancient buildings on the hill. The lake takes up over half of the park area. Let's walk along the lake,cross the bridge and climb up the hill. Then I can pointout the sights of Beijing for you.Tony: Yes, good idea. I'm sure it'll be fantastic to see the city from the top.Daming: But I'm so tired, and it's so hot here. I don't want to climb. The lake looks nice and cool. Why don't we go for a swim?Lingling: I don't think they allow people to swim in the lake. It's dangerous.Daming: That's too bad. Then why don't we have our picnic here? I'm so hungry and thirsty.Lingling: I think it's better to have our picnic at the top of the hill.Tony: Come on! Let's not waste any more time.Daming: All right. I hope it will be cooler up there.Questions:1. Is the Beihai Park noisy?。
八年级下册语文电子书人教版新版
八年级下册语文电子书人教版新版1. 引言八年级下册语文电子书是基于人教版新版教材的电子化内容，旨在帮助八年级学生更方便地学习和复习语文知识。
本文档将介绍八年级下册语文电子书的主要特点和使用方法，希望能为学生们提供更好的学习体验。
2. 特点八年级下册语文电子书具有以下几个特点：2.1 电子化内容语文电子书采用电子化方式呈现，学生可以通过平板电脑、手机等设备随时随地进行阅读。
这样不仅方便了学生的学习，还减轻了他们背负重重教材的负担。
2.2 多媒体辅助语文电子书中融入了丰富的多媒体资源，如音频、视频等。
学生通过观看视频、听取音频可以更直观地理解课文内容，提高学习效果。
2.3 随机功能语文电子书还提供了一些随机功能，如随机抽题、随机演示等。
这些功能可以使学习更加有趣，并提高学生的学习积极性。
2.4 多种解析语文电子书中还配有多种题目解析，帮助学生更好地理解和掌握知识点。
学生可以根据自己的情况选择不同的解析方式，提高解题能力。
3. 使用方法下面将介绍如何使用八年级下册语文电子书。
3.1 下载安装学生可以通过各大应用市场下载并安装八年级下册语文电子书APP，也可以通过教育平台的官方网站下载安装软件包。
3.2 注册登录安装完成后，学生需要注册一个账号并登录。
登录后，可以根据自己的学校和个人信息进行相关设置。
3.3 浏览课文在首页中，可以选择八年级下册相应的教材，浏览课文内容。
点击相应的课文，可以查看具体的内容和相关的知识点。
3.4 学习互动学生可以在电子书中进行学习互动，参与课文讨论、答题、发表评论等。
这样可以加深对知识点的理解，并与他人分享学习体验。
3.5 制定学习计划电子书中还提供了学习计划的功能，学生可以根据自己的学习进度和时间安排，制定合理的学习计划，并进行相应的学习跟进。
4. 总结通过八年级下册语文电子书，学生可以更方便地学习和复习语文知识。
电子化内容、多媒体辅助、随机功能、多种解析等特点，使学习充满趣味性和活力。
湘潭物理八年级下册版电子书
湘潭物理八年级下册版电子书教学准备教学目标1.能够融合实例分析什么就是有用功、额外功和总功。
2.能说出机械效率的含义，知道机械效率是小于1的。
能利用机械效率的公式进行简单计算。
3.通过实验介绍滑轮组机械效率的多寡与物体重力大小有关。
教学重难点机械效率就是重点;测量滑轮组机械效率就是难点。
教学工具多媒体、板书教学过程一、引入环节(2分钟)(一)导入新课，板书课题书香门第小区一户住宅正在翻新中，现在须要把 kg的砂子运往6 m低的楼上。
想想看，下面两种方法哪种更好? 为什么?要解答这个问题需要学习一个新的物理量机械效率。
下面我们就来一起学习第三节机械效率(二)出具自学目标课件展示学习目标，指导学生观看。
同时教师板书课题。
过渡阶段语：介绍了自学目标，恳请根据自学指导深入细致自学课本，时间约7分钟二、先学环节(15分钟)(一)出具自学指导课件展示自学指导，请同学们带着下列问题看课本p85-87页内容，勾划知识点并记忆，可查资料但要独立完成：1.观测p85模拟实验，两次拉力所搞的功一样吗?2.什么叫有用功、额外功、总功?分别用什么表示?三者之间的关系是什么?3.什么叫做机械效率?用什么则表示?表达式就是什么?4.机械效率为什么总小于1?5.写作p87实验，实验之前须要测量哪几个量，怎样排序有用功，怎样排序总功?6.哪些方法可以提高机械效率?7分钟后比谁能够恰当顺利完成检测题。
准备工作展现(二)学生自学教材：师巡视(三)自学检测意见反馈要求：5分钟完成自学检测题，让4个小组的的同学到黑板前展示，书写成绩和题目成绩记入小组量化，要求书写认真、规范，下面同学交换学案，小组长组织成员用红笔将错误画出，准备更正。
1.为达至目的必须搞的功叫做 _______功，用______ 则表示;并非我们须要但不得不搞的功叫做_______功，用_______则表示;有用功提额外功是总共搞的功，叫做_______ 功，用 _______ 则表示。
八年级下册数学电子书1
八年级下册数学电子书人教版八年级下册数学课本知识点归纳第十六章分式一、分式1. 分式：如果A 、B 表示两个整式，并且B 中含有字母，那么式子BA叫做分式。
(分式有意义的条件是分母不为零，分式值为零的条件分子为零且分母不为零 )2. 分式的基本性质：分式的分子与分母同乘(或除)以一个不等于0的整式，分式的值不变。
用式子表示如下：（C ≠0）其中A,B,C 是整式3．最简公分母：取各分母的所有因式的最高次幂的积做公分母，它叫做最简公分母4．通分：分子和分母同乘最简公分母，不改变分式值，把几个整式化成相同分母的分式。
这个过程叫通分。
（分母为多项式时要分解因式）5．约分：约去分子和分母的公因式，不改变分式值，这个过程叫约分。
二、分式的运算1．分式乘法法则：分式乘分式，用分子的积作为积的分子，分母的积作为分母。
2．分式除法法则：分式除以分式，把除式的分子、分母颠倒位置后，与被除式相乘。
上述法则可以用式子表示：C B C A B A ⋅⋅=C B C A B A ÷÷=bc ad c d b a d c b a bd ac d c b a =⋅=÷=⋅;上一页下一页3分式乘方法则：一般地，当n 为正整数时这就是说，分式乘方要把分子、分母分别乘方4．分式的加减法则：同分母的分式相加减，分母不变，把分子相加减。
异分母的分式相加减，先通分，变为同分母分式，然后再加减。
上述法则可用以下式子表示：,a b a b a c ad bc ad bc c c c b d bd bd bd±±±=±=±= 5．整数指数幂1．任何一个不等于0的数的0次幂等于1，即)0(10≠=a a ；当n 为正整数时，n n a a 1=- （)0≠a ，也就是说a n (a≠0)是a -n 的倒数。
正整数指数幂运算性质也可以推广到整数指数幂．(m,n 是整数)（1）同底数的幂的乘法：n m n m a a a +=⋅；（2）幂的乘方：mn n m a a =)(;（3）积的乘方：n n n b a ab =)(；（4）同底数的幂的除法：n m n m a a a -=÷( a ≠0)；（5）商的乘方：n nn b a ba =)(( n 是正整数)；(b ≠0) 三、分式方程1. 分式方程：分母中含未知数的方程叫分式方程。
2020新编教材八下《桃花源记》正规电子书(课文+注释+译文)
新编教材八下《桃花源记》电子书原文晋太元中，武陵人捕鱼为业。
缘溪行，忘路之远近。
忽逢桃花林，夹岸数百步，中无杂树，芳草鲜美，落英缤纷，渔人甚异之，复前行，欲穷其林。
林尽水源，便得一山，山有小口，仿佛若有光。
便舍船，从口入。
初极狭，才通人。
复行数十步，豁然开朗。
土地平旷，屋舍俨然，有良田美池桑竹之属。
阡陌交通，鸡犬相闻。
其中往来种作，男女衣着，悉如外人。
黄发垂髫，并怡然自乐。
见渔人，乃大惊，问所从来。
具答之。
便要还家，设酒杀鸡作食。
村中闻有此人，咸来问讯。
自云先世避秦时乱，率妻子邑人来此绝境，不复出焉，遂与外人间隔。
问今是何世，乃不知有汉，无论魏晋。
此人一一为具言所闻，皆叹惋。
余人各复延至其家，皆出酒食。
停数日，辞去。
此中人语云：“不足为外人道也。
”既出，得其船，便扶向路，处处志之。
及郡下，诣太守，说如此。
太守即遣人随其往，寻向所志，遂迷，不复得路。
南阳刘子骥，高尚士也，闻之，欣然规往。
未果，寻病终，后遂无问津者。
选自《陶渊明集》卷六（中华书局1979年版）注释词句注释1. 太元：东晋孝武帝的年号（376-396）。
2. 武陵：郡名，今湖南常德一带。
3. 缘：顺着、沿着。
4. 鲜美：新鲜美好。
5. 落英：落花。
一说，初开的花。
6. 缤纷：繁多的样子。
7. 异：惊异、诧异。
这里是“对……感到惊异”的意思。
8. 欲穷其林：想要走到那片林子的尽头。
穷：尽。
9. 林尽水源：林尽于水源，桃花林在溪水发源的地方就到头了。
10. 仿佛：隐隐约约，形容看得不真切。
11. 才通人：仅容一人通过。
才，仅仅，只。
12. 豁然开朗：形容由狭窄幽暗突然变得开阔敞亮。
13. 俨（yǎn）然：整齐的样子。
14. 属：类。
15. 阡陌交通：田间小路交错相通。
阡陌，田间小路。
16. 相闻：可以互相听到。
17. 悉：全，都。
18. 外人：桃花源以外的世人，下同。
19. 黄发垂髫（tiáo）：指老人和小孩。
黄发，旧说是长寿的象征，用以指老人。
华东师大版八年级数学下册电子课本
第17章分式 (2)§17.1 分式及其基本性质 (2)1.分式的概念 (2)2.分式的基本性质 (3)§17.2分式的运算 (6)1.分式的乘除法 (6)2.分式的加减法 (7)阅读材料 (9)§17.3可化为一元一次方程的分式方程 (10)§17.4零指数幂与负整指数幂 (13)1.零指数幂与负整指数幂 (13)2.科学记数法 (14)小结 (16)复习题 (16)第17章 分 式现要装配30台机器，在装配好6台后，采用了新的技术，每天的工作效率提高了一倍，结果共用了3天完成任务。
如果设原来每天能装配x 台机器，那么不难列出方程：326306=-+xx这个方程左边的式子已不再是整式，这就涉及到分式与分式方程的问题.§17.1 分式及其基本性质1.分式的概念做一做（1）面积为2平方米的长方形一边长3米，则它的另一边长为_____米； （2）面积为S 平方米的长方形一边长a 米，则它的另一边长为________米； （3）一箱苹果售价p 元，总重m 千克，箱重n 千克，则每千克苹果的售价是______元；形如BA(A 、B 是整式，且B 中含有字母，B ≠0)的式子，叫做分式(fraction ).其中 A 叫做分式的分子(numerator ),B 叫做分式的分母（denominator ）.整式和分式统称有理式（rational expression ）, 即有有理式 整式，分式.例1 下列各有理式中，哪些是整式？哪些是分式？（1）x 1；（2）2x ；（3）yx xy+2；（4）33y x -.解：属于整式的有：（2）、（4）；属于分式的有：（1）、（3）.注意：在分式中，分母的值不能是零.如果分母的值是零，则分式没有意义.例如，在分式aS中，a ≠0；在分式n m -9中，m ≠n.例2 当x 取什么值时，下列分式有意义？（1）11－x ；（2）322+-x x .分析 要使分式有意义，必须且只须分母不等于零. 解 （1）分母1－x ≠0，即x ≠1.所以，当x ≠1时，分式11－x 有意义.（2）分母23+x ≠0，即x ≠-23.所以，当x ≠-23时，分式322+-x x 有意义.2.分式的基本性质在进行分数的化简与运算时，常要进行约分和通分，其主要依据是分数的基本性质.类似地，分式有如下基本性质：分式的分子与分母都乘以（或除以）同一个不等于零的整式，分式的值不变.与分数类似，根据分式的基本性，可以对分式进行约分和通分. 例3 约分（1）4322016xyy x -； （2）44422+--x x x 分析 分式的约分，即要求把分子与分母的公因式约去.为此，首先要找出分子与分母的公因式.解（1）4322016xy y x -＝－y xy xxy 544433⋅⋅＝－y x 54.（2）44422+--x x x ＝2)2()2)(2(--+x x x ＝22-+x x . 约分后，分子与分母不再有公因式. 分子与分母没有公因式称为最简分式.例4 通分 （1）b a 21，21ab ； （2）y x -1，y x +1； （3）221y x -，xyx +21.分析 分式的通分，即要求把几个异分母的分式分别化为原来的分式相等的同分母的分式.通分的关键是确定几个分式的公分母，通常取各分母所有因式的最高次幂的积作为公分母（叫做最简公分母）.例如第（1）小题中的两个分式ba 21和21ab，它们的最简公分母是a 2b 2. 解 （1）b a 21与21ab的最简公分母为a 2b 2，所以b a 21＝b b a b ⋅⋅21＝22b a b ， 21ab ＝aab a ⋅⋅21＝22b a a . （2）y x -1与yx +1的最简公分母为（x -y ）(x +y )，即x 2－y 2，所以y x -1＝))((1y x y x y x +-+⋅）（y x +1＝))(()(1y x y x y x -+-⋅（3）因为 x 2－y 2＝x 2＋xy ＝所以221y x -与xyx +21221yx -＝＿＿＿＿＿＿＿＿＿＿＿， xyx +21＝＿＿＿＿＿＿＿＿＿＿＿. 练 习 1. 约分：（1）2232axy y ax ； （2）)(3)(2b a b b a a ++-； （3）32)()(a x x a --； （4）y xy x 242+-. 2. 通分： （1）231x ，xy125； （2）x x +21，x x -21. 3. 军训期间，小华打靶的成绩是m 发9环和n 发7环，请问，小华的平均成绩是每发多少环？ 习题17.11. 用分式填空：（1） 小明t 小时走了s 千米的路，则他走这段路的平均速度是＿＿＿＿千米/时；（2） 一货车送货上山，上山速度为x 千米/时，下山速度为y 千米/时，则该货车的平均速度为＿＿＿＿千米/时.2. 指出下列有理式中，哪些是分式？x 1， 21（x +y ）， 3x ， x m -2， 3-x x ， 1394y x +3. 当x 取什么值时，下列分式有意义？（1）x 21； （2）22+-x x ； （3）142++x x ； （4）534-x x.4. 通分：（1）ab c 、bc a 、ac b ； （2）x x +21，1212++-x x .5. 某机械厂欲成批生产某种零件，第一道工序需要将一批长l 厘米、底面半径为2r 厘米的圆钢锻造成底面半径为r 厘米的圆钢.请问锻造后的圆钢长多少厘米？§17.2 分式的运算1.分式的乘除法试一试 计算：（1）a b b a 32232⋅； （2）b a b a 232÷.解 （1）a b b a 32232⋅=a b b a 32322⋅⋅=b a32.（2）b a b a 232÷=2232a b b a ⋅=22b a.概括分式乘分式，用分子的积作为积的分子，分母的积作为积的分母.如果得到的不是最简分式，应该通过约分进行化简.分式除以分式，把除式的分子、分母颠倒位置后，与被除式相乘. 例1计算：（1）xb ay by x a 2222⋅； （2）222222x b yz a z b xy a ÷.解 （1）x b ay by x a 2222⋅=x b by ay x a 2222⋅⋅=33b a .（2）222222x b yz a z b xy a ÷=yz a x b z b xy a 222222⋅=33zx .例2计算：.解 原式＝)2)(2()3)(3(32-+-+⋅+-x x x x x x ＝23+-x x .思 考怎样进行分式的乘方呢？试计算：（1）（m n ）3 （2）（mn）k （k 是正整数） （1）（m n ）3 =m n m n m n ⋅⋅＝)()(m m m n n n ••••＝________； （2）（m n ）k =个k m n m n m n ⋅⋅⋅＝)()(m m m n n n •••••• ＝___________. 仔细观察所得的结果，试总结出分式乘方的法则.练 习 1.计算：（1）c a a b ⋅； （2）yx xy xy y x 234322+⋅-； （3）2226103x y x y ÷； （4）2221x x x x x +⋅-. 2.计算： （1）（x y 2-）2 ； （2）（22ca-）33.上海到北京的航线全程s 千米，飞行时间需a 小时；铁路全长为航线长的m 倍，乘车时间需b 小时.飞机的速度是火车速度的多少倍？（用含a 、b 、s 、m 的分式表示）2.分式的加减法试一试 计算：（1）a a b 2+； （2）ab a 322-.解（1）a a b 2+=a b 2+（2）ab a 322-=b a a b a b 2232-=b a ab 232-概括同分母的分式相加减，分母不变，把分子相加减；异分母的分式相加减，先通分，变为同分母的分式，然后再加减.例3计算：xyy x xy y x 22)()(--+.解xy y x 2)(+－xyy x 2)(-＝xyy x y x 22)()(--+＝xy y xy x y xy x )2()2(2222+--++＝xyxy4＝4.例4 计算：1624432---x x . 分析 这里两个加项的分母不同，要先通分.为此，先找出它们的最简公分母.注意到162-x =)4)(4(-+x x ,所以最简公分母是.解 1624432---x x ＝)4)(4(2443-+--x x x ＝)4)(4(24)4)(4()4(3-+--++x x x x x＝)4)(4(24)4(3-+-+x x x＝)4)(4(123-+-x x x＝)4)(4()4(3-+-x x x＝43+x . 练 习 1. 计算：（1）a a 21+； （2）ab ab 610-； （3）； 2. 计算：（1）v u 11+； （2）24aba b -；（3）aa a +--22214； （4）224-++a a .习题17.2 1. 计算：（1）nx my mx ny ⋅； （2）y x yx28712÷；（3）x x x x x x +-÷-+-2221112； （4）223⎪⎭⎫ ⎝⎛-a b . 2. 计算：（1）a c b a c b ++-； （2）bc a c -； （3）xx -++1111； （4）112---x x x . 3. 计算： （1）323111x x x x ⋅⎪⎭⎫⎝⎛+-； （2）⎪⎭⎫ ⎝⎛--+⋅+-y x x y x y x x 2121. 4. 林林家距离学校a 千米，骑自行车需要b 分钟，若某一天林林从家出发迟了c 分钟，则她每分钟应多骑多少千米，才能使到达学校的时间和往常一样？ 5. 周末，小颖跟妈妈到水果批发市场去买苹果.那儿有两种苹果，甲种苹果每箱重m 千克，售a 元；乙种苹果每箱重n 千克，售b 元.请问，甲种苹果的单价是乙种苹果的多少倍？阅读材料历史上的分数运算法则（1）最早的分数运算法则 我们伟大的祖国，作为世界四大文明古国之一，在世界数学发展的历史长河中，曾作出过许多杰出的贡献，远远走在世界的前列.许多光辉的成就，在世界数学史上享有崇高的荣誉.分数运算法则的出现就是我们引以为荣的成就。
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第七章 力
1
第1节 力
2
第2节 弹力
6
第3节 重力
9
第八章 运动和力
15
第1节 牛顿第一定律
16
第2节 二力平衡
20
第3节 摩擦力
23
第九章 压强
第1节 第2节 第3节 第4节
压强 液体的压强 大气压强 流体压强与流速的关系
28 29 33 39 44
目录 1
第十章 浮力
48
第1节 浮力
49
第2节 阿基米德原理
除 了 图 7.2-2 所 示 的实验室常用的几种弹 簧测力计，人们还制造 了其他形式的测力计 （图 7.2-3）。
甲 握力计
乙 弹簧秤 图7.2-3 各种测力计
丙 托盘秤
科学世界 材料的力学性能
材料的力学性能，是指材料受力时的变形行为及其抵抗破坏的能力，通常包括弹 性与塑性、脆性与韧性等。无论是何种材料，一般受力时都要发生形变。有的会发生 弹性形变，有的会发生塑性形变。不同材料发生弹性形变、塑性形变的难易程度不同。
2. 让一位同学
穿上旱冰鞋，向前
推墙（图 7.1-6 乙），
观察发生的现象。
甲 磁体之间的相互作用
图7.1-6 力的作用是相互的
乙 用手推墙
实验结果表明，一个物体对另一个物体施力时，另一个物体也同时对它施 加力的作用。也就是说，物体间力的作用是相互的。
ҮҮᑧߥྫྷူ
1. 请举例说明：（1）力能使物体发生形变；（2）力 能改变物体的运动状态；（3）力的作用效果与力的大小、 方向、作用点有关系。
在研究力的问题中怎样简单、方便地表示力？物理学中通常用一条带箭头
的线段表示力。如图 7.1-5，在受力物体上沿着力的方向画一条线段，在线段
的末端画一个箭头表示力的方向，线 段的起点或终点表示力的作用点。在
ͺၸཁ
F=100 N
同一图中，力越大，线段应该越长。
有时还可以在力的示意图上用数值和
ழՓ
单位标出力的大小。这样用一条带箭
力的作用效果
用 力 捏 橡 皮 泥 ( 图 7.1-1 甲 )，
甲
松开手后，观察橡皮泥有什么变
化；用力压或拉弹簧 ( 图 7.1-1 乙 )，
观察弹簧的形状（长度）发生了怎
样的变化。
用力捏橡皮泥时，橡皮泥的形状
发生了变化。用力压和拉弹簧时，弹簧
的形状也发生了变化。
2 物理 八年级下册
图7.1-1 物体的形状 发生怎样的变化？
2. 用线将吊灯悬挂在天花板上，吊线对灯的拉力 F = 4 N。请在图 7.1-7 中画出拉力 F 的示意图。
3. 一位同学沿水平方向用 75 N 的力推箱子，请在 图 7.1-8 中画出这个力的示意图。
4. 如图 7.1-9，人坐在小船上，用力推另一艘小 船，能够把另一艘小船推开而自己坐的小船不动吗？ 为什么？
想想做做
如图 7.1-4，分别在 A、B、C 处用同样大 小的力推门，感受手推门的难易程度有什么 不同。
A BC
图7.1-4 力作用的位置不 同其作用效果一样吗？
越靠近门轴推门，越费力。可见，不仅力的大小、方向会影响力的作用效
果，力的作用点也会影响力的作用效果。我们把力的大小、方向、作用点叫做
力的三要素。
例题 质量为 0.25 kg 的木块，受到的重力是多少牛？一个人所受的重力
为 450 N，那么，他的质量是多少千克？ g 取 10 N/kg。
解 由 G = mg 可知，木块受到的重力
力不允许超过它的最大测量值，否则会损坏弹簧测力计。 下面让我们通过实验，练习使用弹簧测力计，掌握弹簧测力计的使用方法。
实验
练习使用弹簧测力计
1. 观察弹簧测力计的量程，并认清它的每个小格表示多少牛。
2. 检查弹簧测力计的指针是否指在零刻度线上。测量前应该把指针调节
到零刻度线上。
3. 用手拉弹簧测力计的挂钩，分别使指针指到 1 N、3 N、5 N 的位置，感
8 物理 八年级下册
图7.2-4
图7.2-6 椭圆形 玻璃瓶
第3 节 重力
水总是由高处向低处流；向空中撒开的鱼网，要飘落到水里；向空中抛出 的石块，最终也会落向地面……
甲
乙
图7.3-1 下落的物体
生活中，你可以随处发现像上面一样的例子。这些现象的产生，是因为地 球对它附近的物体有吸引作用。由于地球的吸引而使物体受到的力叫做重力 （gravity），通常用字母 G 表示。地球附近的所有物体都受到重力的作用。
质量m/kg 重力G/N
图7.3-2 测量钩 码所受的重力
2. 在图 7.3-3 中，以质量为横坐
G/N
标、重力为纵坐标描点并连接这些点。
观察后思考：物体所受的重力跟它的
质量之间有什么关系？
精确的实验表明，物体所受的重
力跟它的质量成正比。如果用 G 表示
重力，m 表示质量，g 表示重力与质
量的比值，地球附近的物体所受的
我们在压尺子、拉橡皮筋时，感受到它们对手有力的作用。物体由于发生 弹性形变而产生的力叫做弹力（elastic force）。放在桌面上的水杯受到桌面对 它的支持力，支持力是弹力；桌面受到水杯的压力，压力也是弹力。
物体的弹性有一定的限度，超过了这个限度就不能恢复到原来的形状。例 如，使用弹簧时不能超过它的弹性限度，否则会使弹簧损坏。
头的线段就把力的大小、方向、作用 点都表示出来了。
图7.1-5 用100 N 的力拉车
力的作用是相互的
我们提水桶时，会感到手也受到水桶向下的拉力。可见，不但手对水桶施 加了力，水桶对手也施加了力。
4 物理 八年级下册
想想做做
1. 如图 7.1-6 甲，在两个靠得较近的小车上
分别放一个磁体，松手后观察发生的现象。
量之间有什么关系？我们可以通过实验，测量物体的重力和它的质量，找出二 者之间的关系。
实验
探究重力的大小跟质量的关系 钩码的质量是已知的，实验中可以选取钩码为被 测物体。如图 7.3-2，把钩码挂在弹簧测力计上，当 钩码静止时，弹簧测力计的读数等于钩码所受重力的 大小。 1. 逐次增挂钩码，分别测出它们所受的重力，并 记录在下面的表格中。
ҮҮᑧߥྫྷူ
1. 在“橡皮泥上留下漂亮的指印”“跳板被跳水运
动员压弯（图 7.2-4）”两个现象中，发生的是不是弹性
形变？说说你的理由。
2. 小强用弹簧拉力器锻炼身体，刚拉开时没感到
太费力，可是两手拉开的距离越大，就感到越费力。这
是什么原因？
3. 试分析一个旧弹簧测力计不能准确测量力的原因。
4. 请读出图 7.2-5 中两个弹簧
乙
可见，力能改变物体的形状，使它发生形变。 力除了可以使物体发生形变外，还有其他作用效果吗？
演示 1. 一个小铁球静止在水平桌面上，当一个磁体靠近它时，会出现什么现象？ 2. 让小铁球从斜面上滚下，沿着它的运动方向放一个磁体（图 7.1-2 甲）， 观察小铁球的运动变化情况。
N
S
甲
乙
图 7.1-2 小铁球受到磁体的作用
说的“捏”“拉”“压”“吸引”等概括为“作用”。
这样，我们可以说，力是物体对物体的作用。发生
作用的两个物体，一个是施力物体，另一个是受力
物体。例如，马拉车时，施力物体是马，受力物体
是车；脚蹬自行车踏板时，施力物体是脚，受力物
体是踏板（图 7.1-3）。 在物理学中，力用符号 F 表示，它的单位是牛
图 7.1-3 脚蹬自行车踏板
图7.1-7 吊灯
图7.1-8 小孩推箱子
图7.1-9 小孩推船
第七章 力 5
第2 节 弹力
轻压一把直尺，使它发生形变，撤去压力，直 尺会恢复原状；把橡皮筋拉长，松手后，橡皮筋会 恢复原来的长度。撑竿跳高运动员将撑竿压弯，松 手后，撑竿也会恢复原状（图 7.2-1）。
弹力
图7.2-1 撑竿跳高
直尺、橡皮筋、撑竿等，在受力时会发生形变，不受力时，又恢复到原来 的形状，物体的这种性质叫做弹性。有些物体，如橡皮泥，形变后不能自动地 恢复到原来的形状，物体的这种性质叫做塑性。
顿（newton），简称牛，符号是 N。托起两个鸡蛋
所用的力大约是 1 N。
第七章 力 3
力的三要素和力的示意图
用力越大，弹簧被拉得越长（或压得越短）；打台球时，击球用力的大小 和方向都会影响球能否入袋。更多的事实告诉我们：力的大小、方向不同，作 用效果就不同。除了大小和方向以外，还有什么会影响力的作用效果？
想想议议
飞机投放的物资，受到地球对它的重力作用，会落向地面的目的地。 你能举出几个例子来证明重力的存在吗？
如果没有重力，我们的生活会是个什么样子？
重力的大小
托起质量不同的物体，会感觉所用的力不同。大量的生活经验告诉我们， 质量不同的物体所受的重力不同。那么，地球附近的物体所受的重力跟它的质
第七章 力 9
第七章 力 7
有些材料当受力达到一定值时，会发生突然断裂，且无明显的塑性形变，这种性 质叫做脆性。例如，轻轻一掰，饼干就会变成碎片。
力学性能是选择材料的重要指标。 1986 年 1 月 28 日，挑战者号航天飞机在升空时意外爆炸，举世震惊。在随后的 事故调查中，物理学家费恩曼用一个简单的实验说明了问题的原因：航天飞机上有一 个环形圈零部件，它嵌在火箭两个部件的接合处，以防止燃料在燃烧时从缝隙泄漏出 来。发射当天的天气非常寒冷，环形圈变得非常坚硬，密封效果变差，造成燃料泄漏， 酿成惨剧。 随着科技的发展，人们逐渐发明了很多具有特殊力学性能的新材料。有的材料不 但很轻，而且强度很高，例如铝合金、碳纤维等。有的合金材料还具有形状记忆功能， 用这种材料制作的产品，经过冷却，可以揉做一团，等到受热后，形状会自动恢复。
3. 再次让小铁球从斜面上滚下。在它运动路径的侧旁放一个磁体（图7.1-2乙）， 观察小铁球的运动变化情况。