第一篇：初二英語(yǔ)下學(xué)期Unit 1教案2

初二英語(yǔ)下學(xué)期Unit 1教案： 課題：Unit 1 Reading(2)

課型：鞏固課

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：初二英語(yǔ)下學(xué)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：初二下學(xué)期教案

第七章密度與浮力

第一、二節(jié)質(zhì)量、學(xué)習(xí)使用天平和量筒

一、基本要求

1、能從物質(zhì)的形態(tài)、形狀、空間位置等的變化中提取物體所含物質(zhì)多少的不變性這一本質(zhì)的東西，從而認(rèn)識(shí)質(zhì)量是物體的一種基本屬性，即用科學(xué)抽象的方法建立質(zhì)量的概念。

2、能從怎樣比較質(zhì)量多少的方法中領(lǐng)悟質(zhì)量單位的意義，以及知道國(guó)際單位制中質(zhì)量單位“千克”的由來(lái)。

3.熟悉常用的質(zhì)量單位，并能對(duì)這些常用的單位形成具體的觀念，對(duì)常見(jiàn)物體質(zhì)量多少有一種基本的估測(cè)能力。

4.認(rèn)識(shí)一些測(cè)量質(zhì)量的工具，熟悉托盤(pán)天平的主要結(jié)構(gòu)。

5.通過(guò)宇宙中物質(zhì)質(zhì)量尺度的數(shù)量級(jí)階的展示，以及認(rèn)識(shí)物質(zhì)的質(zhì)量這一基本屬性，樹(shù)立唯物辯證的思想，拓展視野，打開(kāi)思路。

6.會(huì)讀產(chǎn)品說(shuō)明書(shū)，能參照說(shuō)明書(shū)正確調(diào)節(jié)與使用托盤(pán)天平，并養(yǎng)成讀用產(chǎn)品說(shuō)明書(shū)的習(xí)慣。

7.能區(qū)分量筒和量杯，會(huì)正確使用量筒和量杯。

二、重點(diǎn)內(nèi)容

質(zhì)量的概念、質(zhì)量的測(cè)量、質(zhì)量各單位間的相互換算和體積的測(cè)量

三、教學(xué)過(guò)程 1.質(zhì)量的引入

講臺(tái)、課桌、鐵錘、鐵釘物理學(xué)中稱為物體，組成這些物體的木材、鐵叫“物質(zhì)”。由上面的觀察看出：講臺(tái)、課桌含有木材的多少不同；鐵錘、鐵釘含鐵的多少也不同。物理學(xué)中用“質(zhì)量”表示物體所含物質(zhì)的多少。

一個(gè)牙膏皮。(a)將它卷起來(lái)，形狀變了，它的質(zhì)量變不變？應(yīng)該注意的是形狀變化指物體彎曲、伸長(zhǎng)、壓扁等形變，并不是指物體削去一部分或增加一部分。(b)將它從南京帶到北京，位置變了，它的質(zhì)量變不變？（c）裝有冰塊的帶蓋玻璃杯，容器內(nèi)的冰全部熔化成水，狀態(tài)變了，它的質(zhì)量變不變？當(dāng)然物體中含有的物質(zhì)多少?zèng)]有變化，當(dāng)然物體的質(zhì)量也不發(fā)生變化?？梢?jiàn)物體的質(zhì)量不隨物體的形狀、位置、狀態(tài)而改變。

要注意生產(chǎn)和生活中通常講的“質(zhì)量”與物理學(xué)中“質(zhì)量”的意義不同。生產(chǎn)和生活中通常講的“質(zhì)量”，著重在“質(zhì)”，物質(zhì)材料的品質(zhì)、產(chǎn)品的品質(zhì)（包括性能、耐用程度）等等，要注意防止只重視“量”忽視了“質(zhì)”。物理學(xué)中把物體含有物質(zhì)的多少叫做質(zhì)量，是物質(zhì)的量，著重在“量”。兩個(gè)物體的質(zhì)量相等，可以是不同品質(zhì)的材料，例如可以一個(gè)是金塊、另一個(gè)是蠟塊，只要含有物質(zhì)的量一樣多。2.質(zhì)量的單位：

千克是國(guó)際上通用的質(zhì)量單位，用kg來(lái)表示?，F(xiàn)在保存在巴黎國(guó)際計(jì)量局中的國(guó)際千克原器是底面直徑和柱高均為39mm的鉑銥合金圓柱體，它的質(zhì)量是1kg的標(biāo)準(zhǔn)。為了方便，還有比千克大的單位噸（t），比千克小的單位克(g)、毫克(mg)。

1噸=10千克、1千克=10克、1克=10毫克

1分米的純水,它的質(zhì)量就是1千克。（下表是一些物體的質(zhì)量）

3.質(zhì)量的測(cè)量

日常生活中買糧、買菜，稱出的都是貨物的質(zhì)量。常用測(cè)質(zhì)量的器具有桿秤、臺(tái)秤、案秤、電子秤。它們各有各的優(yōu)缺點(diǎn)。

我們今天來(lái)學(xué)習(xí)托盤(pán)天平的使用。首先我們來(lái)看一下托盤(pán)天平的構(gòu)造。

托盤(pán)天平由底座、刀口、托盤(pán)兩只、稱量標(biāo)尺和游碼、橫梁和平衡螺母、分度標(biāo)尺和指針等組成。

托盤(pán)天平在使用之前必須進(jìn)行調(diào)節(jié)，調(diào)節(jié)的目的是使橫梁平衡，調(diào)節(jié)的手段或措施是調(diào)節(jié)平衡螺母，橫梁平衡的標(biāo)志是指針指在了分度標(biāo)尺的中間或是在分度標(biāo)尺的中央左右均勻擺動(dòng)。無(wú)論是橫梁左端的平衡螺母還是橫梁右端的平衡螺母，其調(diào)節(jié)的方向是一致的，也就是與指針的傾斜方向相反。

①天平必須置于水平臺(tái)面上。

②游碼撥到最左端的零位置。

③調(diào)節(jié)橫梁兩端的平衡螺母使橫梁上指針指在分度盤(pán)的中線處。若指針指在分度盤(pán)中線左側(cè)，則需把平衡螺母向右移動(dòng)，反之就向左移動(dòng)。

必須指出，調(diào)節(jié)平衡后的天平經(jīng)移動(dòng)后使用前仍要重新調(diào)節(jié)橫梁平衡（也叫做空載平衡），不能直接使用。托盤(pán)天平必須置于水平臺(tái)上使用，將游碼歸零后調(diào)節(jié)平衡螺母使橫梁平衡。

天平調(diào)節(jié)平衡之后，我們就可以使用它來(lái)測(cè)量一些物體的質(zhì)量了。

被測(cè)物放左盤(pán)，砝碼放右盤(pán)，調(diào)節(jié)砝碼與游碼使橫梁恢復(fù)平衡。砝碼加游碼所示的質(zhì)量就是待測(cè)物質(zhì)量，與任何測(cè)量?jī)x器一樣，所測(cè)物質(zhì)量不能超過(guò)天平的最大秤量，也不能小于天平的最小感量。天平屬精密儀器，必須保持清潔、干燥，要注意輕拿輕放。3

333游碼是天平測(cè)量準(zhǔn)確度的標(biāo)志。使用前首先認(rèn)清游碼上的最小刻度值。如圖所示游碼范圍是2g，每一小格表示0.1g．這也就是天平的感量。游碼示數(shù)應(yīng)以游碼的左側(cè)對(duì)齊格數(shù)所示質(zhì)量，圖71所示游碼位置是0.7 g。

稱物體質(zhì)量時(shí)，左盤(pán)放待測(cè)物，右盤(pán)置砝碼，稱量時(shí)首先估測(cè)物體的質(zhì)量，選取砝碼要由大至小順序，以最小砝碼加上后右盤(pán)微翹再移動(dòng)游碼使之平衡．砝碼數(shù)加游碼數(shù)即得物體質(zhì)量。

必須注意的是在調(diào)節(jié)載有物體的天平的橫梁平衡（也叫載物調(diào)平衡）時(shí)，絕對(duì)不允許去移動(dòng)平衡螺母。

稱液體或帶有腐蝕性的物體時(shí)，必須先稱容器的質(zhì)量，再稱容器和待測(cè)物的總質(zhì)量，最后把總質(zhì)量減去容器質(zhì)量就得待測(cè)物質(zhì)量。物理上稱之謂“補(bǔ)差法”。對(duì)于一切易污染、易腐蝕的物體都應(yīng)該采用此法去稱量，絕不可以直接稱量而導(dǎo)致天平損壞。

天平是屬于精密儀器，因此在整個(gè)使用中必須注意：①輕拿輕放，不可讓天平受到強(qiáng)烈振動(dòng)。②干凈衛(wèi)生，不可讓盤(pán)、梁等沾上污物或受到銹蝕。③砝碼必須使用鑷子，不能用手直接取砝碼，保證砝碼的精確。④用后應(yīng)將游碼歸零，砝碼歸盒；橫梁用固定圈固定，保證支架刀口不受損傷從而增強(qiáng)靈敏度。

4.量筒（或量杯）的使用

量筒（或量杯）是用來(lái)測(cè)定液體體積的儀器。利用排液法也可以間接測(cè)定固體的體積。量筒使用前應(yīng)看清量程及每一小格所表示的體積，量筒（或量杯）的所示體積單位一般是mL，即cm。倒入、倒出液體時(shí)應(yīng)小心，不能溢出。尤其是用排水法測(cè)固體體積時(shí)，預(yù)先放入的水要適量，水不能少得淹不住物體，也不能多得溢出量杯。

3讀數(shù)時(shí)要注意兩點(diǎn)：①將量筒（或量杯）置于水平桌面上；②觀察時(shí)視線應(yīng)與筒內(nèi)液體的凸面頂部（如水銀等）或凹面底部（如水等）相平。

第三節(jié) 科學(xué)探究：物質(zhì)的密度

一、基本要求：

1、體驗(yàn)科學(xué)探究的全過(guò)程，熟悉科學(xué)探究的幾個(gè)主要環(huán)節(jié)，如提出問(wèn)題、猜想與假設(shè)、制定計(jì)劃、收集證據(jù)、分析和論證、評(píng)價(jià)與反思、合作與交流。

2、會(huì)應(yīng)用“比值”的方法探究物質(zhì)的性質(zhì)，建立密度的概念，認(rèn)識(shí)密度公式和單位的由

3、學(xué)會(huì)查物質(zhì)的密度表，并能說(shuō)出一些常見(jiàn)物質(zhì)的密度。

4、會(huì)測(cè)量一些物質(zhì)的密度。

5、會(huì)應(yīng)用物質(zhì)的密度解決一些實(shí)際問(wèn)題。

二、重點(diǎn)內(nèi)容：密度的概念、測(cè)量和應(yīng)用；難點(diǎn)內(nèi)容：密度的概念、測(cè)量和應(yīng)用

三、教學(xué)過(guò)程

1、密度概念的引入

我們這個(gè)世界就是由各種各樣的物質(zhì)組成的。如：空氣、水、泥土、石頭、鐵、銅等等。每種物質(zhì)又都有自己的特性。如：空氣是氣體，水是液體，泥土是軟的，石頭是硬的，金屬有光澤，非金屬無(wú)光澤等等。形狀、顏色、軟硬、氣味等這些就是物質(zhì)的特性，我們可以根據(jù)這些特性來(lái)鑒別物質(zhì)。我們可以根據(jù)它的氣味鑒別它是水還是酒精，可以根據(jù)它們的顏色及銹跡，鑒定是銅還是鐵。如果我們桌上放的這兩個(gè)物體，外面涂有同樣的顏色，我們要怎樣判斷它們是什么物質(zhì)呢？

我們鑒別物質(zhì)，有很多時(shí)候，僅靠氣味、顏色、軟硬、形狀等特性是不夠的，那么物質(zhì)是否還有其它特性呢？ 我們可以做這樣一些實(shí)驗(yàn)：A、將涂有同種顏色、同體積的兩物體放在托盤(pán)天平的兩個(gè)盤(pán)上，結(jié)果天平失去平衡．B、取同體積的水和酒精倒入質(zhì)量相等的兩個(gè)空燒杯中，然后分別放到天平的兩個(gè)盤(pán)上，結(jié)果天平也失去平衡。兩物體的體積相同，質(zhì)量不同；水和酒精的體積相同，但質(zhì)量不同．

這說(shuō)明不同物質(zhì)在體積相同時(shí)，質(zhì)量是不同的。這也反映了物質(zhì)的一種特性。為此在物理學(xué)中我們引入一個(gè)新的物理量——密度。

2、密度的概念：密度是表示不同物質(zhì)，在體積相同時(shí)質(zhì)量并不相同這一特性的物理量?，F(xiàn)在我們只知道了涂有同種顏色的兩個(gè)物體不是同種物質(zhì)，還不知道它們各是什么？這就需要我們進(jìn)一步研究：對(duì)于同一種物質(zhì)來(lái)說(shuō)，它的質(zhì)量跟體積有什么樣的關(guān)系。我們可以通過(guò)以下的實(shí)驗(yàn)來(lái)研究。

我們?nèi)〈笮〔煌耐庑我?guī)則的小木塊和小鐵塊，然后用天平稱出鐵塊或木塊的質(zhì)量，用刻度尺測(cè)出其體積，并計(jì)算第一個(gè)物體的質(zhì)量與體積的比值。將這些數(shù)據(jù)填入下表：

我們對(duì)上面的實(shí)驗(yàn)數(shù)據(jù)進(jìn)行分析，看看能得出什么規(guī)律？

體積不同的鐵塊，它們的質(zhì)量不同。鐵塊a的體積是鐵塊b的兩倍，鐵塊a的質(zhì)量就是鐵塊b的兩倍；鐵塊c的體積是鐵塊b的4倍，鐵塊c的質(zhì)量就是b的4倍．木塊a的體積是木塊b的兩倍，木塊a的質(zhì)量就是木塊b的兩倍；木塊c的體積是木塊b的四倍，木塊c的質(zhì)量就是木塊b的四倍。

但是對(duì)鐵塊來(lái)說(shuō)，每一個(gè)鐵塊的質(zhì)量和體積的比值是個(gè)定值；對(duì)木塊來(lái)說(shuō)，每一個(gè)木塊的質(zhì)量和體積的比值也是個(gè)定值。只是這兩個(gè)比值不相等而已。

對(duì)于同種物質(zhì)，它的體積增大幾倍，它的質(zhì)量也增大幾倍，即它的質(zhì)量和它的體積成正比，質(zhì)量和體積的比值是個(gè)定值．對(duì)不同物質(zhì)，這個(gè)比值不同；而質(zhì)量跟體積的比值就等于單位體積物質(zhì)的質(zhì)量，不同種類物質(zhì)單位體積的質(zhì)量一般不同，可見(jiàn)單位體積的質(zhì)量反映了物質(zhì)的特性，物理學(xué)中就用單位體積的質(zhì)量來(lái)定義密度。密度的定義：某種物質(zhì)單位體積的質(zhì)量叫做這種物質(zhì)的密度。用符號(hào)“ρ”來(lái)表示． 密度的公式：ρ=m/V，m表示質(zhì)量，V表示體積。

密度公式的意義包含有：(1)不同物質(zhì)的物體，質(zhì)量相等時(shí)，密度較大的物體其體積較小，如：質(zhì)量相等的銅塊和鐵塊，銅塊體積小于鐵塊體積。即當(dāng)質(zhì)量相等時(shí)，體積跟密度成反比。(2)不同物質(zhì)的物體，體積相等時(shí)，密度較大的物體其質(zhì)量較大。如：同一個(gè)瓶裝滿水和裝滿油相比較，裝滿水的質(zhì)量大。即當(dāng)體積相同時(shí)，質(zhì)量跟密度成正比。

由密度公式可知，密度的單位是由質(zhì)量單位和體積單位組成的。在國(guó)際單位制中，質(zhì)量的單位是kg，體積的單位是m，密度的單位就是kg/m，讀作千克每立方米。

在一般物理實(shí)驗(yàn)中，由于所用物質(zhì)不多，因此質(zhì)量的單位常用克，體積的單位常用厘米，密度的單位就是g/cm。1g/cm=1kg/1000÷1m/10=10kg/m,記?。?g/cm=10kg/m

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3密度的實(shí)用單位除g／cm外還可用kg／dm和t／m，有時(shí)使用這些單位能使計(jì)算簡(jiǎn)化。

密度是表征物質(zhì)特性的物理量。它表示單位體積的某種物質(zhì)的質(zhì)量大小。每種物質(zhì)都有一定的密度，與物體的質(zhì)量大小、體積大小無(wú)關(guān)，它只與物質(zhì)的種類有關(guān)（平均密度則由物體的質(zhì)量和體積來(lái)決定）。如：1g水和1kg水密度是相同的。不同的物質(zhì)密度一般是不相同的。如：鐵與鋁的密度，油與水的密度都不相同。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。

自然界的物質(zhì)種類很多，有的已經(jīng)被人們所認(rèn)識(shí)，有的尚未被認(rèn)識(shí)，人類還在不斷地發(fā)現(xiàn)新的物質(zhì)，下面是科學(xué)家經(jīng)過(guò)精密的測(cè)量，所測(cè)出的一些常見(jiàn)物質(zhì)的密度，我們稱其為密度表。我們看表：

銅的密度是8.9×10千克／米，這表示體積是1米的銅的質(zhì)量是8.9×10千克，用克／厘米作單位，它的數(shù)值是8.9，即8.9克／厘米；鐵的密度是7.9×10千克／米3

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3。銅的密度比鐵大，說(shuō)明1米體積的銅的質(zhì)量比1米體積鐵的質(zhì)量大。

水的密度是1.0×10千克／米；水的密度還有一個(gè)規(guī)律性的知識(shí)，也就是1米的3

33水的質(zhì)量為1噸；1分米的水的質(zhì)量為1千克；1厘米的水的質(zhì)量是1克；1毫米的質(zhì)量是1毫克。記住這個(gè)規(guī)律對(duì)以后的解決問(wèn)題是相當(dāng)有好處的。所以同學(xué)們一定要記住它．

空氣的密度是l.29千克／米。另外還請(qǐng)同學(xué)們注意看，在氣體的密度表旁邊有個(gè)條件—0℃，在標(biāo)準(zhǔn)大氣壓下。其實(shí)不僅是氣體，固體和液體的密度也都是在一定條件下由科學(xué)家經(jīng)過(guò)嚴(yán)格準(zhǔn)確的實(shí)驗(yàn)測(cè)出的，一般固體和液體的密度大小是同一數(shù)量級(jí)，氣體的密

333度比它們小1000倍左右．

現(xiàn)在，我們?cè)倏疵芏缺?，比較固體、液體、氣體的密度，我們發(fā)現(xiàn)固體的密度都較大；氣體的密度都比較小。是不是所有的物質(zhì)都是這樣呢？當(dāng)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。水銀的密度是13.6×10千克／米，水銀是液體，可它的密度卻比一些固體的密度還要大，所以說(shuō)固體的密度較大，只是對(duì)一般物體而言。

若有一種金屬，它的密度是2.7×10千克／米，它是什么金屬？由密度表可知，這種金屬是鋁．所以，利用密度還可以鑒別物質(zhì)。

綜上所述，密度表一處，同學(xué)們要從兩個(gè)方面來(lái)學(xué)習(xí)。一方面，知道物質(zhì)，根據(jù)密度表，同學(xué)們要能查到其密度值，并知道其物理意義；另一方面，知道了某種物質(zhì)的密度值，根據(jù)密度表，同學(xué)們應(yīng)該知道這是什么物質(zhì)。

3、密度知識(shí)的應(yīng)用：（1）鑒別物質(zhì)

由于通過(guò)物質(zhì)的密度我們就可以知道這是什么物質(zhì)，所以我們就可以根據(jù)物質(zhì)的密度來(lái)鑒別物質(zhì)?？磥?lái)要鑒別物質(zhì)，首先要學(xué)習(xí)測(cè)量物質(zhì)的密度。

由密度的定義可知，要想測(cè)量密度，首先要測(cè)出質(zhì)量，在實(shí)驗(yàn)室中我們一般用到的測(cè)量工具是天平。然后要測(cè)量被測(cè)物體的體積。質(zhì)量的測(cè)量這里我們不多講，我們重點(diǎn)來(lái)講體積的測(cè)量。對(duì)于形狀不規(guī)則的物體，我們可以利用量筒或量杯來(lái)進(jìn)行。首先我們將量筒或量杯中放入適量（所謂適量，就是當(dāng)放入被測(cè)物體后，水既要將被測(cè)物體全部浸沒(méi)，水又不能超出量筒或量杯的最大刻度。）的水，記下此時(shí)量筒或量杯中水的體積V1；然后用細(xì)線系住被測(cè)物體，輕輕的放入水中記下水和物體的總體積V2，用V2—V1即可求出被測(cè)物體的體積。如果物體的密度比水的密度小，這時(shí)將它放入水中它將漂浮在水面上，這時(shí)我們也是不能測(cè)出物體的體積的。這時(shí)我們常用兩種方法來(lái)測(cè)其體積。一種方法是用助沉法。（用其它密度大的物體和被測(cè)物體系在一起，沉入水中，當(dāng)然這時(shí)助沉物的體積應(yīng)該在V1中。）另一種方法是用細(xì)針將其按入水中，觀察V2。當(dāng)然如果物體的形狀是規(guī)則的，或是可以將其分割成規(guī)則物體，我們就可以利用刻度尺來(lái)測(cè)量其體積了。

液體密度測(cè)量時(shí)，體積比較容易測(cè)量，用量筒或量杯就行了，關(guān)鍵是液體質(zhì)量的測(cè)量。首先我們要測(cè)出燒杯中液體和杯子的總質(zhì)量m1,然后將液體倒入量筒或量杯中一部分，用天平測(cè)出剩余液體和杯子的總質(zhì)量m2。液體的質(zhì)量m=m1—m2。

（2）求質(zhì)量：天安門(mén)廣場(chǎng)的人民英雄紀(jì)念碑，它的碑心石是一整塊巨大的花崗巖，它長(zhǎng)14.7m、寬2.9m、厚1m。怎樣知道它的質(zhì)量？

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3這塊碑心石的質(zhì)量非常大，不容易找到能測(cè)出其質(zhì)量的測(cè)量工具。但我們可以采用有關(guān)密度的知識(shí)來(lái)解決。首先我們知道了它的材質(zhì)是花崗巖，從密度表中我們可查找出這種物質(zhì)的密度為（2.6～2.8）×10千克/米。它的物理意義是體積為1米的花崗巖，它的質(zhì)量是（2.6～2.8）×10千克，我們就取2.8×10千克/米吧。這樣看來(lái)，我們只要知道這塊石頭的體積不就能求出質(zhì)量了嗎？而這個(gè)物體是一個(gè)形狀規(guī)則的物體，其體積是容易計(jì)算的。

從密度的計(jì)算公式ρ=m/V可以得出m=ρV 這個(gè)式子告訴我們，物體的質(zhì)量等于它的密度乘以體積。因此，知道了物體的體積，查出組成物質(zhì)的密度，就可以算出它的質(zhì)量，對(duì)于不能直接稱量的龐大物體，這是求質(zhì)量的很方便的辦法．（3）求體積

這里有1個(gè)鋁制的機(jī)器零件，不用量筒或量杯能測(cè)出這個(gè)零件的體積嗎？

從公式??mm還可以得出V?V?

利用這個(gè)式子，知道了物體的質(zhì)量，查出它的密度，就可以算出它的體積，對(duì)于形狀不規(guī)則的或不便于直接測(cè)量的較大的物體，這是求體積的很方便的辦法．求出物體的體積之后，我們就可以根據(jù)體積與高度（長(zhǎng)度或厚度）與橫截面積的關(guān)系，就可以求出物體的長(zhǎng)度（高度或是厚度）或者求出物體的截面積。

第四篇：初二英語(yǔ) 2

★初二英語(yǔ)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.★初二英語(yǔ)日記：體育課

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.★根據(jù)以下情況寫(xiě)一篇短文介紹你的這位筆友

李華，英文名叫Tony，是第一中學(xué)一年級(jí)二班的學(xué)生．他出生于1989年8月12日．他的出生地在廣東深圳．他今年13歲，愛(ài)好音樂(lè)和籃球．他喜歡英語(yǔ)，愛(ài)玩電腦游戲．他經(jīng)常放學(xué)后與同學(xué)打籃球． B)寫(xiě)短文介紹,開(kāi)頭已給出

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.★兩件生日禮物(Two Britihday Gifts)共兩篇

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.

第五篇：初二下學(xué)期英語(yǔ)教學(xué)計(jì)劃

初一英語(yǔ)教學(xué)計(jì)劃

這次初一的教材，難度比以前高，記憶背誦的單詞量多，而且對(duì)知識(shí)的遷移，對(duì)學(xué)生的靈活運(yùn)用等要求較高。因此，所以我們必須加大力度提高課堂、課后學(xué)習(xí)英語(yǔ)的效率，避免眼高手低，單詞不過(guò)關(guān)，基礎(chǔ)掌握不牢固的現(xiàn)象，盡量讓學(xué)生都能盡最大可能學(xué)好英語(yǔ)。特實(shí)施下面幾點(diǎn)措施：

1）狠抓教學(xué)常規(guī)，重點(diǎn)放在差生的管理上。如經(jīng)常檢查筆記 及作業(yè)，多進(jìn)行個(gè)別輔導(dǎo)，培養(yǎng)他們良好的學(xué)習(xí)習(xí)慣和紀(jì)律行為。

2）以落實(shí)書(shū)本知識(shí)為主，對(duì)知識(shí)重，難點(diǎn)精講精練。

3)多組織單元測(cè)試，以定期進(jìn)行質(zhì)量分析，發(fā)現(xiàn)問(wèn)題，及時(shí) 采取措施。

4）認(rèn)真批改作業(yè)，加強(qiáng)作業(yè)講評(píng)。

5）注重培養(yǎng)學(xué)生學(xué)英語(yǔ)的方法和好習(xí)慣，多讀；多聽(tīng)；多練； 多說(shuō)。

6）提高課堂45分鐘的效率，讓學(xué)生學(xué)得好，學(xué)得輕松愉快。

7）組織自主互助學(xué)習(xí)型課堂，開(kāi)展“結(jié)對(duì)子”活動(dòng)，以優(yōu)帶 差，互助。

8）進(jìn)行寫(xiě)作訓(xùn)練，提高寫(xiě)作能力。

教學(xué)進(jìn)度安排：

.一周一個(gè)話題，中間再進(jìn)行期中復(fù)習(xí)，時(shí)間這學(xué)期是寬裕的。