第一篇：初二英语下学期Unit 1教案2

初二英语下学期Unit 1教案： 课题：Unit 1 Reading(2)

课型：巩固课

1.Knowledge aims:

Words: southern, till, married, wife, over, cinema, turn, factory, waste, pollute, realize, reduce, open, lonely, throw,husband, interview Phrases:

Get married, over the years, turn into, used to, take action, reduce the pollution, in some ways, open space, feel a bit lonely, from time to time, throw away

2.Ability aims: 1.To enable the students to use the phrases and sentences patterns.2.To revise and expand vocabulary in the context of times have changed 3.To skin the text for overall meaning and scan for detail.3.Emotion targets:

Make the students learn happily and use freely 4.Key points: 1.The factory used to dump its waste into the river.2.Later, the governmet realized it was a very serious problem and too action to reduce the pollution.3.Present perfect tense 5.Teaching procedures: 1.Review some words e.g.unhappy, arrive, ground, teeth, husband, wife

2.tell students to refer to the reading passage to find the words listed in PartB in context.Ask students to try to do the exercise without referring to the reading passage.3.Ask students to complete Part B by matching the words with the definitions and writing the correct letters in the blanks

4.Check answers as a quiz.Read the definitions in random order and students have to say the correct words.5.Explain the context of Part C1.Millie is telling Sandy about her interview with Mr.Dong

6.Divide the class into pairs.Ask students to take turns reading the statements and checking whether they are true or false.7.Review answers as a class.Ask students to give the line number in the passage where the correct information can be found.Ask more able students to correct the false statements

8.Ask more able students to do the extra exercise.6.Homework: Do some exercises

第二篇：初二英语下学期教案Lesson 53-56

Lesson 53: Ringing Up Li Ming Teaching Content: Mastery words and expressions: ring, ring up Oral words and expressions: ring up, What does…mean? Hold on, please.This is…speaking, a few Teaching Aims: 1.Learn to make a telephone call in English.2.Know about the following culture.Teaching Important Points: 1.How to make a telephone call.2.What does “ring up” mean in the U.K.? Teaching Difficult Points: How to make a telephone call? Teaching Preparation: a telephone Teaching Aids: audiotape, flashcards, a telephone Type of lesson: new lesson Teaching Procedure: Step1.First sing the song together.Step2.Ask the students if they have previewed the lesson.Let the students ask questions about the lesson.Work in pairs.Ask and answer questions about this lesson.They can ask like this: 1.What does “Ring up” mean in Canada? 2.Is Li Ming at home? Step3.Listen to the tape and try to finish Exercise 2 in activity book.1.What would Brian like to do for his report on Asia? 2.Who tells Brian Li Ming’s telephone number? 3.What time is it in China when it is afternoon in Canada? 4.Does Brian ring up Li Ming’s apartment? 5.How is the weather in Shijiazhuang? 6.Can Li Ming help Brian with his report? Step4.Read the text and check the answers.First let the students read the text silently.Then read it in roles.After a while, ask some students to come to the front and act the dialogue out.Step5.Explain the main expressions in this text.Make up sentences with “May I speak to…?” “This is….speaking.” “Who’s that’s?”

Step6.Discuss the details of this lesson.What questions can the students ask? Can others find the right answer? Step7.Come to “LET’S DO IT!” Step8.Homework 1.Finish off the exercises in activity book.2.Go on the next reading in the student book.Summary: Ringing up is the main content of this lesson.Making a telephone call is so different from Chinese.It is a good teaching tip to give the students more time to practice in class.Lesson 54: Europe Teaching Content: Mastery words and expressions: England, European, sea Oral words and expressions: German, Italian, Greek, the Alps, the Caspian Sea, the Volga River, Moscow, Paris, the Triumphal Arch Teaching Aims: 1.Know more about the world’s geography.2.Compare the physical features with the Asian physical features.Teaching Important Points: 1.Learn about the physical features of Europe.2.Know about the customs and habits in Europe.Teaching Difficult Points: the physical features of Europe Teaching Preparation: a map of the world Teaching Aids: audiotape, flashcards, a map of the world Type of lesson: new lesson Teaching Procedure: Step1.Make up a telephone dialogue.Let the students act it out in front of the class.Step2.Listening task Listen and finish the exercises: 1.The world’s ________ smallest continent is Europe.2.Europe has more than thirty __________.3.________ is the biggest country in Europe.And London is one of the largest _______.Step3.Reading task 1.How big is Europe? 2.What countries are in Europe? 3.How many people live in Europe? 4.What languages do Europeans speak? 5.What are the main geographical features of Europe? 6.What are the biggest cities in Europe? Step4.Read comprehension First read the text silently.Then read the text loudly.If they have some trouble, let’s listen to the tape again.Step5.Read the text again.Encourage the students to ask questions.Discuss the details in class.Step6.Practice

Write some words and expressions on the blackboard.Such as: Europe, Britain, French, German, Russian, Italian, the Alps, the Caspian Sea, the Volga River Step7.Talk about the countries and the languages that they speak.Country

Language England

English France

French Germany

German Russia

Russian Italy

Italian Greece

Greek Step8.Homework 1.Finish off the exercises in activity book.2.Go on the next reading in the student book.Summary: Many words and expressions are too difficult for the students to read.So write them on the blackboard and read them loudly.It refers many languages in this lesson.Sum the content and present to the class in order to make them remember more clearly.Lesson 55: Report on the Report!Teaching Content: Mastery words and expressions: interview, on Oral words and expressions: province, go/be abroad Teaching Aims: 1.Learn about the foreign culture and customs.2.Know about more about the world’s geography.Teaching Important Points: 1.Sum what we learn in this unit.2.Master something about the geography.Teaching Difficult Points: Demonstrate the things that have passed.Pay attention to the indefinite pronouns.Teaching Preparation: pictures Teaching Aids: audiotape, flashcards, pictures Type of lesson: new lesson Teaching Procedure: Step1.Review the countries and the languages.Let some students make a list on the blackboard.Step2.Listening task Listen and finish Exercise 2 in activity book.Answer true(T)or false(F)1.Li Ming kept thinking about Brian’s report today in school.2.Li Ming didn’t tell his mother about Brian’s geography class.3.Most people in North America know Shijiazhuang well.4.Brian’s report was the only one with an interview.5.Brian’s teacher thought talking to people from other parts of the world is a good way to learn geography.6.Danny gave a very good report on Asia.7.The Europe’s longest river is in England.Step2.Read and check the answers.First read silently.Then read it loudly in class.The teacher walks around the classroom to see if the students need some help.Step3.Read the text again.Then discuss the questions in listening task.Discuss the details with the students to see if they have some questions to ask.Step4.Make up sentences with the language points: Keep doing: I keep thinking practicing the spoken English.With an interview: Beijing is a city with many places of interest

Step5.Listen to the tape again.Pay attention to the intonation and pronunciation.Step6.Let some students sum the main content in this lesson, but not word by word.Step7.Come to “LET’S DO IT”.Step8.Homework 1.Finish off the exercises in activity book.2.Do the exercises on Page 69.Summary: How to express one’s idea in English is difficult for the students.Sometimes they understand the words but they don’t know how to use them.The teacher should spend some time on written English.Writing is an important ability for the students.It must be cultivated in daily English class.Lesson 56: Unit Review Teaching Content: Mastery words and expressions from Lesson 50 to Lesson 55.Oral words and expressions from Lesson 50 to Lesson 55.Teaching Aims: 1.Know the main geographical features of the world.2.Be familiar to the Internet.Teaching Important Points: 1.Learn about the foreign culture.2.Know about the situation of our country.Teaching Difficult Points: The names of some places, including the places in China and foreign countries.Teaching Preparation: a globe, a map of China, a map of the world Teaching Aids: audiotape, flashcards, a globe, a map of China, a map of the world

Teaching Procedure: Step1.Look at the map of China.Introduce the main places of China.Discuss the places of interest in China.Step2.Look at the map of the world.Point out the seven continents and four oceans on the map.Introduce the situation in the seven continents.Step3.Look at the globe and sing the song in Lesson 52.Let volunteers come to the front and sing the song.Do a survey: How many students can sing the song? Do they all have good listening ability? Step4.Finish the exercises in this lesson.Step5.Check if they have some difficulties.Explain them on the blackboard.Step6.Come to “Do You Know”? First let the students read together.Then ask them to sum the main meaning of this part.At last, make up sentences with the important grammars.Step7.Homework 1.Read the text of Unit 7 in activity book.2． Finish the writing exercises.Summary: The knowledge in the book is limited.Encourage the students to get more from the Internet and other books.Let the students present what they get in the class.They can improve their communicate ability.They also learn to use the Internet and tools.5

第三篇：初二英语 2

★初二英语范文：忙碌的星期六(Busy Saturdays)

I don't like Saturday at all.Because I am too busy to enjoy myself.In the morning, I go to school to have classes from 8:00 to 11:30.In the afternoon, I play the violin with the classmates from 2:00p.m.to 4:00p.m..In the evening, I have to go to an evening school.When I get back, I only want to have a sound sleep.Sometimes I'm as busy as a bee.I would like to have a free Saturday of my own.★初二英语日记：体育课

May 28th, Monday, Cloudy

This afternoon we had a PE lesson.Our teacher taught us to practise the long jump.When the bell rang, we gathered on the playground.After warming-up exercises, the teacher told us the way of long jump and showed us how to do it.Then we followed the teacher and practised one after another.Soon it was my turn, but I felt a hit nervous.Though I failed the first time, I didn't lose my heart yet.I continued practising.At last I was able to jump over 3 meters.From this lesson I realized that one will succeed if he doesn’t give up early.★根据以下情况写一篇短文介绍你的这位笔友

李华，英文名叫Tony，是第一中学一年级二班的学生．他出生于1989年8月12日．他的出生地在广东深圳．他今年13岁，爱好音乐和篮球．他喜欢英语，爱玩电脑游戏．他经常放学后与同学打篮球． B)写短文介绍,开头已给出

I have a good pen pal.Let me tell you something about him.________________________________________________________________ I have a good penfriend.Let me tell you something about him.His name is Li Hua.He has an English name.It is Tony.He is a middle school student in Class Two, Grade One of No.1 Middle School.He is 13 years old now.He was born in

Shenzhen, Guangdong.His birthday is August 20th.He likes playing basketball and listening to music.He often plays basketball with his classmates after school.His favourite subject is English and he likes playing computer games best.I like to write to him.He is my good friend.★两件生日礼物(Two Britihday Gifts)共两篇

第一篇

It was my birthday yesterday.I got a lot of gifts.All of them were covered with coloured paper.Among them there were two interesting ones.My elder sister gave me a round paper bag and I thought it was a football.But when I opened it, it was a clock.My brother gave me a message, saying that “My present has been put in your bedroom.”As soon as I went into my bedroom,I found a box.I opened it and found a laptop.I was very happy.These two presents aim to let me study hard and not to waste time.第二篇

Yesterday was my birthday and I received a lot of presents.These presents were packed in coloured paper and two of them were funny and interesting, which impressed me.My sister sent a bag of present to me.The bag was big and round.I though it was a football.But when I opened it, I saw a clock.The other one was given by my brother.He left me a message, which said “my present is lying in your bedroom”.When I got to my bedroom, I found a laptop.Oh!Great!＇ I jumped with joy.I know, they want me to study hard and not to waste time.I would never forget this birthday.A Day in my mother’s life

My mother is an engineer.She is always in hurry.6.30a.m.The clock is ringing.My mother gets up quickly, wash.Then she goes in kitchen.She will cook breakfast for my family.8.30a.m.She arrives at company.Begin to read messenger.She must be the first one to the office.This is a busy morning.Many things haven’t over.My mother walks around the company.Different tings with different people.There are many telephones for her, the work is so hard!5p.m.One day’s work is over.What a long day she has.It’s time to relax.My mother plays badminton twice a week to keep healthy.And on Friday she usually goes shopping.7.30p.m.She always eats dinner on her desk.She works on computer at home.The messenger tells her many things about the company in other countries.She has to talk to the people from these companies on internet.11.30p.m.She doesn’t sleep much.After dinner she continues working on the computer until she finishes woks.But she can have break at weekends.I always say that my mother is a very busy woman.A day in my uncle's life

My uncle is a taxi driver.His life is not so relax because he is busy.He always gets up early.He washes, puts on his uniform.He has breakfast alone.Then he starts working.He drives people to lots of places.He knows Shanghai's terrain very well.He always eat some bread instead lunch.He sometimes drives taxi all night.So he feels tired.He is not very healthy.He needs much sleep.A day in my life

I am a middle school student.Here is my daily life.I wake up early.Then l put on my uniform and wash.I take a bus to school.l always have breakfast at school.If it doesn’t rain, we will have morning exercise at 8:00a.m.After that, we have classes.l always try my best to learn some basic subjects.I also learn some efficent ways to study from others.So l

achieve A grades in most subjects.In P.E.lessons, I do physical sports to be healthy and strong.I go to library after lunch twice a week.After school, l return home with my friends by bus.I usually finish my homework before dinner.In the evening, l always go to bed before 9:30.I think we should have a healthy life style.It’s very important.A Day in my life

I am a student ofXinglong Middle School.Every day, there is much work for me.When the clock rang at 6 a.m., I got up.After finishing the things before leaving, I went school.As usual, mum drove me to school.After morning exercise, I had eight lessons.In the free time, I helped the teachers do some work.I finished school at half past four.When I arrived home, I started doing my homework.I often finished it at about 7 p.m., And today, it was the same.I had dinner with my family.Up to now, I have finished much work.I think I may have a rest.A day in my aunt’s life

She is a policeman.She likes her job very much.She gets up at 6P.m.She washes, has breakfast and puts on her uniform.It makes her awesome.She takes a bus to the police office every day.After she gets the police office, she starts working.First she asks the leader what to do.She usually answers the phone in her office.Sometimes she patrols the streets.She works almost the whole week but she never complains about it.She usually returns home at 6 p.m.She likes eating healthy food like vegetables.She usually goes to bed before 12p.m.A Day In My Life

I get up at 6 a.m.Then I wash and put on my school uniform.After a quick breakfast, I walk to school.It take me about half an hour.At 8 a.m., I start school.Most of subjects are interesting.I often achieve A grades.I usually get home at about 5 o’clock.I do my homework at night.It takes me about an hour.I usually go to bed before 10 p.m.

第四篇：初二下学期教案

第七章密度与浮力

第一、二节质量、学习使用天平和量筒

一、基本要求

1、能从物质的形态、形状、空间位置等的变化中提取物体所含物质多少的不变性这一本质的东西，从而认识质量是物体的一种基本属性，即用科学抽象的方法建立质量的概念。

2、能从怎样比较质量多少的方法中领悟质量单位的意义，以及知道国际单位制中质量单位“千克”的由来。

3.熟悉常用的质量单位，并能对这些常用的单位形成具体的观念，对常见物体质量多少有一种基本的估测能力。

4.认识一些测量质量的工具，熟悉托盘天平的主要结构。

5.通过宇宙中物质质量尺度的数量级阶的展示，以及认识物质的质量这一基本属性，树立唯物辩证的思想，拓展视野，打开思路。

6.会读产品说明书，能参照说明书正确调节与使用托盘天平，并养成读用产品说明书的习惯。

7.能区分量筒和量杯，会正确使用量筒和量杯。

二、重点内容

质量的概念、质量的测量、质量各单位间的相互换算和体积的测量

三、教学过程 1.质量的引入

讲台、课桌、铁锤、铁钉物理学中称为物体，组成这些物体的木材、铁叫“物质”。由上面的观察看出：讲台、课桌含有木材的多少不同；铁锤、铁钉含铁的多少也不同。物理学中用“质量”表示物体所含物质的多少。

一个牙膏皮。(a)将它卷起来，形状变了，它的质量变不变？应该注意的是形状变化指物体弯曲、伸长、压扁等形变，并不是指物体削去一部分或增加一部分。(b)将它从南京带到北京，位置变了，它的质量变不变？（c）装有冰块的带盖玻璃杯，容器内的冰全部熔化成水，状态变了，它的质量变不变？当然物体中含有的物质多少没有变化，当然物体的质量也不发生变化。可见物体的质量不随物体的形状、位置、状态而改变。

要注意生产和生活中通常讲的“质量”与物理学中“质量”的意义不同。生产和生活中通常讲的“质量”，着重在“质”，物质材料的品质、产品的品质（包括性能、耐用程度）等等，要注意防止只重视“量”忽视了“质”。物理学中把物体含有物质的多少叫做质量，是物质的量，着重在“量”。两个物体的质量相等，可以是不同品质的材料，例如可以一个是金块、另一个是蜡块，只要含有物质的量一样多。2.质量的单位：

千克是国际上通用的质量单位，用kg来表示。现在保存在巴黎国际计量局中的国际千克原器是底面直径和柱高均为39mm的铂铱合金圆柱体，它的质量是1kg的标准。为了方便，还有比千克大的单位吨（t），比千克小的单位克(g)、毫克(mg)。

1吨=10千克、1千克=10克、1克=10毫克

1分米的纯水,它的质量就是1千克。（下表是一些物体的质量）

3.质量的测量

日常生活中买粮、买菜，称出的都是货物的质量。常用测质量的器具有杆秤、台秤、案秤、电子秤。它们各有各的优缺点。

我们今天来学习托盘天平的使用。首先我们来看一下托盘天平的构造。

托盘天平由底座、刀口、托盘两只、称量标尺和游码、横梁和平衡螺母、分度标尺和指针等组成。

托盘天平在使用之前必须进行调节，调节的目的是使横梁平衡，调节的手段或措施是调节平衡螺母，横梁平衡的标志是指针指在了分度标尺的中间或是在分度标尺的中央左右均匀摆动。无论是横梁左端的平衡螺母还是横梁右端的平衡螺母，其调节的方向是一致的，也就是与指针的倾斜方向相反。

①天平必须置于水平台面上。

②游码拨到最左端的零位置。

③调节横梁两端的平衡螺母使横梁上指针指在分度盘的中线处。若指针指在分度盘中线左侧，则需把平衡螺母向右移动，反之就向左移动。

必须指出，调节平衡后的天平经移动后使用前仍要重新调节横梁平衡（也叫做空载平衡），不能直接使用。托盘天平必须置于水平台上使用，将游码归零后调节平衡螺母使横梁平衡。

天平调节平衡之后，我们就可以使用它来测量一些物体的质量了。

被测物放左盘，砝码放右盘，调节砝码与游码使横梁恢复平衡。砝码加游码所示的质量就是待测物质量，与任何测量仪器一样，所测物质量不能超过天平的最大秤量，也不能小于天平的最小感量。天平属精密仪器，必须保持清洁、干燥，要注意轻拿轻放。3

333游码是天平测量准确度的标志。使用前首先认清游码上的最小刻度值。如图所示游码范围是2g，每一小格表示0.1g．这也就是天平的感量。游码示数应以游码的左侧对齐格数所示质量，图71所示游码位置是0.7 g。

称物体质量时，左盘放待测物，右盘置砝码，称量时首先估测物体的质量，选取砝码要由大至小顺序，以最小砝码加上后右盘微翘再移动游码使之平衡．砝码数加游码数即得物体质量。

必须注意的是在调节载有物体的天平的横梁平衡（也叫载物调平衡）时，绝对不允许去移动平衡螺母。

称液体或带有腐蚀性的物体时，必须先称容器的质量，再称容器和待测物的总质量，最后把总质量减去容器质量就得待测物质量。物理上称之谓“补差法”。对于一切易污染、易腐蚀的物体都应该采用此法去称量，绝不可以直接称量而导致天平损坏。

天平是属于精密仪器，因此在整个使用中必须注意：①轻拿轻放，不可让天平受到强烈振动。②干净卫生，不可让盘、梁等沾上污物或受到锈蚀。③砝码必须使用镊子，不能用手直接取砝码，保证砝码的精确。④用后应将游码归零，砝码归盒；横梁用固定圈固定，保证支架刀口不受损伤从而增强灵敏度。

4.量筒（或量杯）的使用

量筒（或量杯）是用来测定液体体积的仪器。利用排液法也可以间接测定固体的体积。量筒使用前应看清量程及每一小格所表示的体积，量筒（或量杯）的所示体积单位一般是mL，即cm。倒入、倒出液体时应小心，不能溢出。尤其是用排水法测固体体积时，预先放入的水要适量，水不能少得淹不住物体，也不能多得溢出量杯。

3读数时要注意两点：①将量筒（或量杯）置于水平桌面上；②观察时视线应与筒内液体的凸面顶部（如水银等）或凹面底部（如水等）相平。

第三节 科学探究：物质的密度

一、基本要求：

1、体验科学探究的全过程，熟悉科学探究的几个主要环节，如提出问题、猜想与假设、制定计划、收集证据、分析和论证、评价与反思、合作与交流。

2、会应用“比值”的方法探究物质的性质，建立密度的概念，认识密度公式和单位的由

3、学会查物质的密度表，并能说出一些常见物质的密度。

4、会测量一些物质的密度。

5、会应用物质的密度解决一些实际问题。

二、重点内容：密度的概念、测量和应用；难点内容：密度的概念、测量和应用

三、教学过程

1、密度概念的引入

我们这个世界就是由各种各样的物质组成的。如：空气、水、泥土、石头、铁、铜等等。每种物质又都有自己的特性。如：空气是气体，水是液体，泥土是软的，石头是硬的，金属有光泽，非金属无光泽等等。形状、颜色、软硬、气味等这些就是物质的特性，我们可以根据这些特性来鉴别物质。我们可以根据它的气味鉴别它是水还是酒精，可以根据它们的颜色及锈迹，鉴定是铜还是铁。如果我们桌上放的这两个物体，外面涂有同样的颜色，我们要怎样判断它们是什么物质呢？

我们鉴别物质，有很多时候，仅靠气味、颜色、软硬、形状等特性是不够的，那么物质是否还有其它特性呢？ 我们可以做这样一些实验：A、将涂有同种颜色、同体积的两物体放在托盘天平的两个盘上，结果天平失去平衡．B、取同体积的水和酒精倒入质量相等的两个空烧杯中，然后分别放到天平的两个盘上，结果天平也失去平衡。两物体的体积相同，质量不同；水和酒精的体积相同，但质量不同．

这说明不同物质在体积相同时，质量是不同的。这也反映了物质的一种特性。为此在物理学中我们引入一个新的物理量——密度。

2、密度的概念：密度是表示不同物质，在体积相同时质量并不相同这一特性的物理量。现在我们只知道了涂有同种颜色的两个物体不是同种物质，还不知道它们各是什么？这就需要我们进一步研究：对于同一种物质来说，它的质量跟体积有什么样的关系。我们可以通过以下的实验来研究。

我们取大小不同的外形规则的小木块和小铁块，然后用天平称出铁块或木块的质量，用刻度尺测出其体积，并计算第一个物体的质量与体积的比值。将这些数据填入下表：

我们对上面的实验数据进行分析，看看能得出什么规律？

体积不同的铁块，它们的质量不同。铁块a的体积是铁块b的两倍，铁块a的质量就是铁块b的两倍；铁块c的体积是铁块b的4倍，铁块c的质量就是b的4倍．木块a的体积是木块b的两倍，木块a的质量就是木块b的两倍；木块c的体积是木块b的四倍，木块c的质量就是木块b的四倍。

但是对铁块来说，每一个铁块的质量和体积的比值是个定值；对木块来说，每一个木块的质量和体积的比值也是个定值。只是这两个比值不相等而已。

对于同种物质，它的体积增大几倍，它的质量也增大几倍，即它的质量和它的体积成正比，质量和体积的比值是个定值．对不同物质，这个比值不同；而质量跟体积的比值就等于单位体积物质的质量，不同种类物质单位体积的质量一般不同，可见单位体积的质量反映了物质的特性，物理学中就用单位体积的质量来定义密度。密度的定义：某种物质单位体积的质量叫做这种物质的密度。用符号“ρ”来表示． 密度的公式：ρ=m/V，m表示质量，V表示体积。

密度公式的意义包含有：(1)不同物质的物体，质量相等时，密度较大的物体其体积较小，如：质量相等的铜块和铁块，铜块体积小于铁块体积。即当质量相等时，体积跟密度成反比。(2)不同物质的物体，体积相等时，密度较大的物体其质量较大。如：同一个瓶装满水和装满油相比较，装满水的质量大。即当体积相同时，质量跟密度成正比。

由密度公式可知，密度的单位是由质量单位和体积单位组成的。在国际单位制中，质量的单位是kg，体积的单位是m，密度的单位就是kg/m，读作千克每立方米。

在一般物理实验中，由于所用物质不多，因此质量的单位常用克，体积的单位常用厘米，密度的单位就是g/cm。1g/cm=1kg/1000÷1m/10=10kg/m,记住：1g/cm=10kg/m

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3密度的实用单位除g／cm外还可用kg／dm和t／m，有时使用这些单位能使计算简化。

密度是表征物质特性的物理量。它表示单位体积的某种物质的质量大小。每种物质都有一定的密度，与物体的质量大小、体积大小无关，它只与物质的种类有关（平均密度则由物体的质量和体积来决定）。如：1g水和1kg水密度是相同的。不同的物质密度一般是不相同的。如：铁与铝的密度，油与水的密度都不相同。由于水的密度比油大，因此一滴水的密度仍要比一桶油的密度大。

自然界的物质种类很多，有的已经被人们所认识，有的尚未被认识，人类还在不断地发现新的物质，下面是科学家经过精密的测量，所测出的一些常见物质的密度，我们称其为密度表。我们看表：

铜的密度是8.9×10千克／米，这表示体积是1米的铜的质量是8.9×10千克，用克／厘米作单位，它的数值是8.9，即8.9克／厘米；铁的密度是7.9×10千克／米3

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3。铜的密度比铁大，说明1米体积的铜的质量比1米体积铁的质量大。

水的密度是1.0×10千克／米；水的密度还有一个规律性的知识，也就是1米的3

33水的质量为1吨；1分米的水的质量为1千克；1厘米的水的质量是1克；1毫米的质量是1毫克。记住这个规律对以后的解决问题是相当有好处的。所以同学们一定要记住它．

空气的密度是l.29千克／米。另外还请同学们注意看，在气体的密度表旁边有个条件—0℃，在标准大气压下。其实不仅是气体，固体和液体的密度也都是在一定条件下由科学家经过严格准确的实验测出的，一般固体和液体的密度大小是同一数量级，气体的密

333度比它们小1000倍左右．

现在，我们再看密度表，比较固体、液体、气体的密度，我们发现固体的密度都较大；气体的密度都比较小。是不是所有的物质都是这样呢？当然不是的，干松木的密度是0.5×10千克／米，它的密度比水的密度小。水银的密度是13.6×10千克／米，水银是液体，可它的密度却比一些固体的密度还要大，所以说固体的密度较大，只是对一般物体而言。

若有一种金属，它的密度是2.7×10千克／米，它是什么金属？由密度表可知，这种金属是铝．所以，利用密度还可以鉴别物质。

综上所述，密度表一处，同学们要从两个方面来学习。一方面，知道物质，根据密度表，同学们要能查到其密度值，并知道其物理意义；另一方面，知道了某种物质的密度值，根据密度表，同学们应该知道这是什么物质。

3、密度知识的应用：（1）鉴别物质

由于通过物质的密度我们就可以知道这是什么物质，所以我们就可以根据物质的密度来鉴别物质。看来要鉴别物质，首先要学习测量物质的密度。

由密度的定义可知，要想测量密度，首先要测出质量，在实验室中我们一般用到的测量工具是天平。然后要测量被测物体的体积。质量的测量这里我们不多讲，我们重点来讲体积的测量。对于形状不规则的物体，我们可以利用量筒或量杯来进行。首先我们将量筒或量杯中放入适量（所谓适量，就是当放入被测物体后，水既要将被测物体全部浸没，水又不能超出量筒或量杯的最大刻度。）的水，记下此时量筒或量杯中水的体积V1；然后用细线系住被测物体，轻轻的放入水中记下水和物体的总体积V2，用V2—V1即可求出被测物体的体积。如果物体的密度比水的密度小，这时将它放入水中它将漂浮在水面上，这时我们也是不能测出物体的体积的。这时我们常用两种方法来测其体积。一种方法是用助沉法。（用其它密度大的物体和被测物体系在一起，沉入水中，当然这时助沉物的体积应该在V1中。）另一种方法是用细针将其按入水中，观察V2。当然如果物体的形状是规则的，或是可以将其分割成规则物体，我们就可以利用刻度尺来测量其体积了。

液体密度测量时，体积比较容易测量，用量筒或量杯就行了，关键是液体质量的测量。首先我们要测出烧杯中液体和杯子的总质量m1,然后将液体倒入量筒或量杯中一部分，用天平测出剩余液体和杯子的总质量m2。液体的质量m=m1—m2。

（2）求质量：天安门广场的人民英雄纪念碑，它的碑心石是一整块巨大的花岗岩，它长14.7m、宽2.9m、厚1m。怎样知道它的质量？

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3这块碑心石的质量非常大，不容易找到能测出其质量的测量工具。但我们可以采用有关密度的知识来解决。首先我们知道了它的材质是花岗岩，从密度表中我们可查找出这种物质的密度为（2.6～2.8）×10千克/米。它的物理意义是体积为1米的花岗岩，它的质量是（2.6～2.8）×10千克，我们就取2.8×10千克/米吧。这样看来，我们只要知道这块石头的体积不就能求出质量了吗？而这个物体是一个形状规则的物体，其体积是容易计算的。

从密度的计算公式ρ=m/V可以得出m=ρV 这个式子告诉我们，物体的质量等于它的密度乘以体积。因此，知道了物体的体积，查出组成物质的密度，就可以算出它的质量，对于不能直接称量的庞大物体，这是求质量的很方便的办法．（3）求体积

这里有1个铝制的机器零件，不用量筒或量杯能测出这个零件的体积吗？

从公式mm还可以得出VV

利用这个式子，知道了物体的质量，查出它的密度，就可以算出它的体积，对于形状不规则的或不便于直接测量的较大的物体，这是求体积的很方便的办法．求出物体的体积之后，我们就可以根据体积与高度（长度或厚度）与横截面积的关系，就可以求出物体的长度（高度或是厚度）或者求出物体的截面积。

第五篇：初二英语下学期作文

(一)My favorite TV Program

The News Report is my favorite TV program.Almost every day I turn on the TV at 6:30 p.m.and wait for the news program.This has become a part of my life.There is something new and important about the world in The News Report, such as the international situation and the latest sports news.we can learn about the information in a short time.In my opinion, the News Report is more than a TV program.It is a way of communication.From this program, people can know and understand world better.The world becomes smaller and smaller.So I especially like it.（二）假期你有什么打算，写一篇60词左右有关你的假期打算的短文。： 1.visit family and friends ２ go somewhere new

2.do some exercises 4.helpfamily do some housework.Summer holidays are coming.During the holidays, at first I’ll have a good rest.Then every day I’ll do morning exercises.And in the afternoon ,If I am free.I’ll go fishing in the park.I like reading ,so I would like to spend more time reading books.During the holidays , I’ll help my parents do some housework.I also want to visit some friends and relatives.I am sure I’ll have a good time this summer.（三）你的朋友汤姆和迈克想游览泰山，请向他们介绍一下大体情况。开头已经给出，注意书信的结尾格式。提示：1.位于山东省泰安市，是山东省最高的山。2.因云海（the sea of clouds）、奇松(wondrous pines)、怪石(unique rocks)、和日出而闻名。3.可步行上山，也可乘缆车。4.山顶风景秀丽，有很多庙宇(temples)Dear Tom and Mike,I’m glad you will visit Mount Tai.Now let me tell you something about it.Mount Tai lies in Tai’an, Shandong.It’s very high and it’s the highest mountain in Shandong Province.It’s famous for the sea of clouds, wondrous pines, unique rocks and sunrise.Every year, many visitors go there for sighting.They say it’s a magic land of mountains , forests and rivers.You can climb up to the top or you can take the cable car as you like.when you get to the top, you will have a wonderful view.There are many temples on the top of the mountains.You can enjoy the beautiful views there.May you have a good time.Love,X X

(四)你的笔友Jack 想知道有关中国春节的一些习俗，请你用80到100个词介绍一下中国的春节，开头和结尾已经给出。

The Spring Festival is the most important festival for the Chinese people

Allfamily members will get together to have a big meal on the New Year’s Eve.We’ll watch the fireworks and eat dumplings.And some families will sit together to chat or watch the get-together of CCTV.It’s a big and special programme.Almost every family will watch it until 12 o’clock.During the spring festival，people can visit their relatives or friends.It’s also a happy time for children.They can get a red package from parents and grandparents , or relatives , and there is money in it.Sothe children are very happy during the festival.Isn’t it interesting? Write to me soon.Yours，Cindy

（五）Write about your hero.The topic is “ the hero in my heart”(我心目中的英雄)

The hero in my heart

There are lots of famous persons in the world and they are like stars in the sky.For me , I think Liu Xiang is a real hero.Many years ago ,all the people in the world think that Asians were not good at running.However Liu Xiang changed their minds.He got the first place.This was the first Asian to win 110m hurdles at the Olympic Games.He ran like a flying horse.He tried his best。At last ,he won the Olympic championship.We all jumped, clapped with joy for his success.All the Chinese people are proud of him.We can imagine how hard he has worked for the race.Liu Xiang is the hero in my heart.I hope he can do better in the 202_ Olympic games.Good luck to you , Liu Xiang!

(六)My perfect holiday

I went toQinghai last summer holiday.I went there by train and my parents went with me，I had a good time.First，whenwe got there，we founda hotel to live inand then had a rest in order to feel good to visit.Then，we went to a museum，I learn about lots of things，it is funny。We also took some beautifulphotos there.We had a picnic in a park, it was delicious.Finally, we went swimming, I feel so happy that I could not forget it.In my opinion，I enjoyed my holiday，I think it is perfect.（七）写作要点：1.上海位于中国的东部，是中国最大的城市。

2.拥有悠久的历史，以外滩而著名。

3.是旅游观光与购物的好地方。因为这里可以买到许多时尚的东西。有许多有趣好玩的地

方供你游玩。

4.去上海的最好季节是春天，天气既不冷，也不热，而夏天雨水较多。

Shanghai lies in the east of China.It is the biggest city.it is a city with long history.And it is famous for the Bund.Shanghai is a good place to go sightseeing for journey.You can buy fashionable things.There are many interest places for you to visit.It is the best time to go to shanghai in spring.It is neither cold nor hot.But in summer it rains often ,you had better take an umbrella with you.Wish you a good trip!

（八）经过初中两年学习，下学期就要上初三了。请对自己前两年的学习做一个简单的回顾，谈谈上初三后的打算。

1.回顾初中两年的学习生活情况，好的和不足的方面。举例说明。

2.上初三后有什么打算。具体的做法两三条。

3.约80词左右。

Time passes away.I will be a Junior Three student.I feel a little nervous and excited.In the past two years, I learned plenty of knowledge.I thought, asked, laughed, cried„„I tried my best to learnwith the help of the teachers and my dear friends, I made much progress.I was so proud of myself.I was thankful to the helpers too.but I did badly inlearning English.andI was very careless and selfish.I spent too much time playing.In this year,I will listen to teachers carefully in class.I will finish my homework on time.I will spend more time learning.I will do some sports after school to keep healthy as well.if I work hard, I can achieve my goal finally!

九）提示：假如你是李平，你昨天（7月17日）在昆明湖游泳感冒了，今天觉得头痛，你母亲给你量了体温后，发现你发烧，便带你去看医生，医生说你要卧床休息两天。请您给陈老师写一张请假条。

Dear Mr.Chen :July 17th

I had a cold afer I swam in the Kunming Lake.And I had a headache.then my mother took my temperature.And found I had a high fever.So she took me to see a doctor, the doctor looked me over,he said that I had to stay in bed for two days.soI have to have two days off.Please allow me to do so。

Thank you!

Liping2