
問題:1、對田納西河流域進(jìn)行開發(fā)能產(chǎn)生哪些方面的效益?2、如果只 提高土地利用程度,是否能保證其他方面的效益不受影響?如果受影響分別說明產(chǎn)生了什么后果?應(yīng)如何治理?這體現(xiàn)了地理環(huán)境的什么特性。(學(xué)生讀課文歸納總結(jié))讀問題研究內(nèi)容,思 考下列問題1、 阿斯旺大壩位于哪個國家?它的建立為該國農(nóng) 業(yè)生產(chǎn)提供了哪些有利條件?2、 阿斯旺大壩的建立帶來了哪些經(jīng)濟(jì)效益?又產(chǎn)生了哪些不利影響?3、 我們應(yīng)如何評價這一工程利與弊?它對我國三峽大壩的建設(shè)有什么借鑒意義。同學(xué)們,通過本課的學(xué)習(xí)我們已深切地感受到河流流域的綜合開發(fā)給我們的生活帶來了巨大的改變,但我們更應(yīng)看到人類的 經(jīng)濟(jì)活動對生態(tài)環(huán)境產(chǎn)生的不利影響,怎樣才能趨利避害,造福人類,這是我們每個人都應(yīng)思考的問題。

三、指導(dǎo)第一段的背誦,點(diǎn)撥理解句意,強(qiáng)調(diào)關(guān)鍵詞語,注重文言基礎(chǔ)知識教學(xué)。過程中要讓學(xué)生反復(fù)讀背。背誦線索:時間——地點(diǎn)——事件——人物——環(huán)境——活動——天氣——感覺。時間:永和九年,歲在癸丑,暮春之初。地點(diǎn):會于會稽山陰之蘭亭。事件:修稧事也。人物:群賢畢至,少長咸集。環(huán)境:此地有崇山峻嶺,茂林修竹;又有清流激湍,映帶左右?;顒樱阂詾榱饔x曲水,列坐其次。雖無絲竹管弦之盛,一觴一詠,亦足以暢敘幽情。天氣:是日也,天朗氣清,惠風(fēng)和暢。感覺:仰觀宇宙之大,俯察品類之盛,所以極視聽之娛,信可樂也。四、學(xué)生自讀背誦5分鐘。五、抽一至二名學(xué)生試背課文,教師可作必要的線索提示。第二課時一、聽名家示范朗誦,學(xué)生小聲跟讀。二、復(fù)習(xí)鞏固第一自然段的閱讀背誦。三、朗讀、解析第二自然段,理解文章“由敘入感”的寫作結(jié)構(gòu)。

結(jié)合歷史自古以來,江山美人歷來都是引無數(shù)英雄豪杰競折腰的,如果說英雄選擇了美人卻丟了江山,把所有罪名都?xì)w結(jié)于“女人是禍水”。但是,紂王無道,和有了妲己有必然的聯(lián)系嗎?有人說妲己壞透了,壞透了的妲己如果不是取得紂王的信任是壞不起來的,紂王聽信了妲己的讒言,聽與不聽決定權(quán)在紂王,而不在妲己。強(qiáng)勢永遠(yuǎn)在紂王一邊。再來看看西施和楊貴妃:西施是作為越國貢獻(xiàn)給吳國的供品來到吳王夫差的身邊的,楊貴妃更是先是李隆基的兒媳婦被看中而得寵的。所以,西施和楊貴妃這兩個可憐的女人根本沒有自己的獨(dú)立選擇,沒有獨(dú)立的愛情,如果沒有西施,就會有南施,或北施;如果沒有楊貴妃,就會有李貴妃,王貴妃,總之什么施,什么妃是不能少的,因?yàn)槟鞘菂峭鹾屠盥』男枰?/p>

一、內(nèi)容與解析從古代運(yùn)用天文方法確定耕作時間,到現(xiàn)代對宇宙形成演變的種種假設(shè),對宇宙的探索,已經(jīng)成為人類生活的一部分。宇宙從何而來,向何而去,人類從何而來,向何而去,這些基本問題不僅具有科學(xué)意義,而且具有哲學(xué)的意味。以前教材中沒有出現(xiàn)過解說詞,但是在日常生活中,我們經(jīng)常接觸到各類解說詞,可以讓學(xué)生聯(lián)系實(shí)際,了解解說詞的特點(diǎn);也可以找來其他科學(xué)電視片,結(jié)合視覺畫面,讓學(xué)生全面地感受解說詞的特點(diǎn)。二、教學(xué)目標(biāo)及解析(一)教學(xué)目標(biāo)1.引導(dǎo)學(xué)生聯(lián)系實(shí)際,了解解說詞的特點(diǎn)。2.引導(dǎo)學(xué)生了解一些有關(guān)宇宙的基礎(chǔ)知識。3.引導(dǎo)學(xué)生借助文中精辟的議論和熱烈的情感抒發(fā),了解作者對宇宙和人類的思考,并引發(fā)自己的思考。

小結(jié)人們對待祥林嫂這個“嫁而再寡”的不幸女人態(tài)度:①、魯四老爺?shù)膽B(tài)度:不讓她干祭祀的活(71、73、75、108通過四嬸先后三喊“你放著罷”,殺人不見血地葬送了祥林嫂的性命。而其中尤以最后一次對其打擊最大)。魯四老爺站在頑固維護(hù)封建宗法制度的立場上,從精神上殘酷地虐殺她。他暗暗地告誡四嬸的那段話,就是置祥林嫂于死地而又不露一絲血痕的軟刀子。②、魯四嬸的態(tài)度:魯四嬸是“大戶人家的太太”,頭一次留祥林嫂是看她能干,祥林嫂被婆家綁架走以后,她害怕給自己家惹麻煩。之后她惦念祥林嫂不是因?yàn)殛P(guān)心她的命運(yùn),而是自己的傭人都沒有祥林嫂那樣可心。以后祥林嫂再來,她“起初還躊躕”,后來倒是真心憐憫祥林嫂,留下她。但是祥林嫂不像過去那樣靈活能干了,四嬸開始“不滿”,進(jìn)而“警告”,最后把祥林嫂趕出家門。可以說,四嬸只是把祥林嫂當(dāng)成一件工具罷了,沒有把她當(dāng)人來看。

B重點(diǎn)與難點(diǎn)重點(diǎn):伽利略對物理學(xué)發(fā)展的重大貢獻(xiàn);經(jīng)典力學(xué)的建立;相對論的提出;量子論的誕生。難點(diǎn):物理學(xué)各階段發(fā)展的原因;對科學(xué)發(fā)展創(chuàng)新性的理解。D教學(xué)過程【導(dǎo)入新課】1632年,伽利略撰寫的《關(guān)于托勒密和哥白尼兩大世界體系的對話》科學(xué)巨著出版后,立刻引起教會的恐慌,把伽利略投入監(jiān)獄。教皇烏爾班八世的御用工具——宗教裁判所在1633年6月21日宣布對伽利略的判決:“我們判決你在宗教法庭監(jiān)獄內(nèi)服刑,刑期由我們掌握,為了有益于補(bǔ)贖,命令你在今后3年內(nèi),每周背誦7篇贖罪詩篇……”這一紙胡言,竟使伽利略蒙冤300多年,致死都沒有撤銷判決,甚至死后還被禁止舉行殯禮,不準(zhǔn)葬入圣太克羅斯墓地。那么,是什么原因?qū)е伦诮滩门兴鶎だ宰髁巳绱伺袥Q?我們應(yīng)如何看待伽利略在科學(xué)領(lǐng)域的貢獻(xiàn)?

一、知識與能力:(1)了解中國古代不同時期的文學(xué)特色;(2)了解、詩,詞、歌、賦等各種不同的知識內(nèi)容和形式,知道和掌握一定數(shù)量的名家作品;(3)拓寬文化視野,提高賞析和運(yùn)用古代文學(xué)作品的能力。二、過程與方法:(1)通過教科書及教師提供的材料以及自己的日常積累,通過閱讀,討論,分析,評論了解各個不同時期的文學(xué)發(fā)展特色。(2)通過閱讀,觀察,練習(xí),欣賞,表演,評論,創(chuàng)作等方式積極參與教學(xué);通過獨(dú)立思考或合作學(xué)習(xí)對所學(xué)的內(nèi)容進(jìn)行比較,概括和闡釋;學(xué)會合作學(xué)習(xí)和相互交流。三、情感態(tài)度與價值觀:通過本課學(xué)習(xí),了解中國古代燦爛的文化。通過對文學(xué)家、詩人及其文學(xué)作品的分析,把學(xué)生帶進(jìn)文學(xué)藝術(shù)的殿堂,感受古人的呼吸,思想,情操。增強(qiáng)文化修養(yǎng)。

畫中的諸多圖像反映了畫家對于傳統(tǒng)繪畫因素的吸收。那個懷抱死去孩子的母親圖像,似乎是源自哀悼基督的圣母像傳統(tǒng);手持油燈的女人,使人聯(lián)想起自由女神像的造型;那個高舉雙手仰天驚呼的形象,與戈雅畫中愛國者就義的身姿不無相似之處;而那個張臂倒地的士兵形象,則似乎與意大利文藝復(fù)興早期某些戰(zhàn)爭畫中的形象,有著姻親關(guān)系。由此可以看出,畢加索不僅是一位富于叛逆精神的大膽創(chuàng)新者,同時也是一位尊崇和精通傳統(tǒng)的藝術(shù)家。教師須強(qiáng)調(diào):現(xiàn)代主義美術(shù)是現(xiàn)代美術(shù)流派的總稱,現(xiàn)代美術(shù)流派眾多,多姿多彩,但它們也表現(xiàn)出許多共同的特征。在技法上,它們大都反對傳統(tǒng)的寫實(shí)主義,追求新奇,空間結(jié)構(gòu)錯亂,色彩配置隨意,點(diǎn)線紊亂,缺乏透視可謂它們共有的特點(diǎn)。在創(chuàng)作主旨上,它們都主張強(qiáng)調(diào)自我,表現(xiàn)個人情感和內(nèi)心世界。可以說,現(xiàn)代美術(shù)藝術(shù)再現(xiàn)了20世紀(jì)西方世界的精神狀況。

教學(xué)目標(biāo):1、知識與能力:(1)識記:理性、啟蒙運(yùn)動;伏爾泰、孟德斯鳩、盧梭等偉大的啟蒙思想家及其主張;康德及啟蒙運(yùn)動的影響;(2)理解啟蒙運(yùn)動興起的背景,分析啟蒙思想的巨大影響;(3)認(rèn)識上層建筑對社會發(fā)展的巨大反作用。2、過程與方法:(1)指導(dǎo)學(xué)生用表格法掌握啟蒙運(yùn)動主要代表人物及其思想主張;(2)運(yùn)用比較法加深對啟蒙思想家觀點(diǎn)共性和個性的認(rèn)識。(3)運(yùn)用比較法對比文藝復(fù)興和啟蒙運(yùn)動的異同,說明啟蒙運(yùn)動對人文主義思想的發(fā)展。3、情感態(tài)度與價值觀:(1)通過本課的學(xué)習(xí),讓學(xué)生認(rèn)識到“一定的文化是一定社會的政治和經(jīng)濟(jì)在觀念上和形態(tài)上的反映”;(2)學(xué)習(xí)啟蒙思想家追求真理的精神,培養(yǎng)學(xué)生遠(yuǎn)大的理想與抱負(fù);(3)通過法國啟蒙思想產(chǎn)生的巨大影響的分析,使學(xué)生認(rèn)識意識形態(tài)對社會發(fā)展所起的重大作用,從而提高學(xué)習(xí)理論的自覺性。

This teaching period mainly deals with grammar “The Present Perfect Passive Voice.” To begin with, teachers should lead students to revise what they have learned about the Present Perfect Passive Voice. And then, teachers move on to stress more special cases concerning this grammar。This period carries considerable significance to the cultivation of students’ writing competence and lays a solid foundation for the basic appreciation of language beauty. The teacher is expected to enable students to master this period thoroughly and consolidate the knowledge by doing some exercises. 1. Guide students to review the basic usages of the Present Perfect Passive Voice2. Lead students to learn to use some special cases concerning the Present Perfect Passive Voice flexibly.2. Enable students to use the basic phrases structures flexibly.3. Strengthen students’ great interest in grammar learning.1. Help students to appreciate the function of the Present Perfect Passive Voice in a sentence2. Instruct students to write essays using the proper the Present Perfect Passive Voice.觀察下列句子特點(diǎn),總結(jié)共同點(diǎn)。1.(教材P28)Much has been written about the wonders of the World Wide Web.2.(教材P28)But the Internet has done much more for people than simply make life more convenient.3.(教材P28)Many people have been helped by the club.4.(教材P28)She no longer feels lonely, and her company has become quite successful.5.(教材P32)Today I thought I’d blog about a question that has been asked many times—how do you stay safe online and avoid bad experiences on the Internet?

From the pictures in the text and the title--- choose the best app, we can know that this part is about how to save money by using apps.Step 2 While-listening1. Laura and Xiao Bo are talking about apps. Listen to their conversation and find out what apps they want.Xiao Bo is looking for a(n) exercise app to help him get in shape.Laura would like an app for getting rich and another that will make her grades better.2. Listen again. Are the sentences true T or false F?1). Both of Xiao Bo's apps keep track of the steps he takes._____2). Xiao Bo's second app can help him make a fitness plan._____3). Laura needs an app that will help her get discounts.______4). Laura needs an app that will add money to her bank account._______F T F T3. Listen once more and tick the sentence you hear. Underline the words used to express predictions, guesses, and beliefs.Predictions, Guesses, and Beliefs________It might help me walk more.________My guess is that it wouldn't work.________I imagine this app would help me get fit faster________I suppose that would be good.________I guess you could save a little with this app.________I suppose there would be some problems, too.________I believe this app could help me get thinner.

Q5:What's Jan's next goal?Her next goal is to start a charity website to raise money for children in poor countries.Q6:What can we learn from her experiences?We learn that when we go through tough times, we can find help and support from other people online. We learn that we can feel less lonelyStep 5: While reading---rethinkingQ1: What is Jan’s attitude to the Internet ?Thankful/Grateful, because it has changed her and her life.Q2: What writing skills is used in the article ?Examples(Jan’s example, the 59-year-old man’s and the 61-year-old woman’s example)Q3: Can you get the main idea of the article ?The Internet has changed Jan’s life/Jan’s life has been changed by the Internet.Step 6 Post reading---Retell the storyMuch has been written about the wonders of the World Wide Web. There are countless articles (1)telling(tell) us how the Internet has made our lives more convenient. But the Internet has done a lot (2)more(much) for people than simply make life more convenient. People’s lives (3) have been changed(change) by online communities and social networks so far. Take Jan for example, who developed a serious illness that made her (4)stuck(stick) at home with only her computer to keep (5)her(she) company. She joined an online group (6)where she could share problems, support and advice with others. She considered the ability to remove the distance between people as one of the greatest (7)benefits(benefit). She was so inspired (8)that she started an IT club in which many people have been helped. She has started to learn more about how to use the Internet to make society better. Her next goal is to start a charity website to raise money (9)for children in poor countries. Jan’s life has been (10)greatly(great) improved by the Internet.

8. However, the more polite you are, the less likely it is you will be attacked. 然而, 你越有禮貌, 你被攻擊的可能性就越小。 Step 8 Writing---the articleHow to stay safe in the online chat roomToday I thought I’d blog about a question that has been asked many times--- how do you stay safe online and avoid bad experiences in the online chat room ? I’m not an expert, but many years as a blogger have taught me a thing or two.First of all, there’s the golden rule of the Internet: keep out of what makes you uneasy. Don’t post comments or click on anything. Second, protect your privacy. Don’t give out too much private information like your address, phone numbers, the ID numbers, etc. Third, be polite. If you are polite to others on the Internet, you won’t be attacked in normal situation. Finally, don’t believe in others easily and never meet someone you met online alone. It is very dangerous.Have you had any bad experiences online, or do you have some good advice for staying safe? Post your comments below!Step 9 Pair workExchange drafts with a partner. Use this checklist to help your partner revise his/her draft.1. Does the writer tell the reader what he/she know about the topic ?2. Are the tips and suggestions well organised ?3. Has the writer defined the new words ?4. Does the author include examples, comparison, or explanations ?5. Does the writer end by asking readers to leave comments and/or suggestions ?6. Can you find any grammar or spelling mistakes.Step 6 HomeworkPut up your revised draft in the classroom or read it to your class.

知識和技能 1、 了解區(qū)域工業(yè)化和城市化之間的關(guān)系,以及它們對區(qū)域社會經(jīng)濟(jì)發(fā)展所起的作用 。2、分析導(dǎo)致珠江三角洲工業(yè)化和城市化快速推進(jìn)的諸多思想束縛,并通過比較,認(rèn)識到對外開放政策是其中的關(guān)鍵因素。3、 比較珠江三角 洲的 區(qū)工業(yè)化進(jìn)程的兩個主要階段,歸納出不同時期的主要發(fā)展特點(diǎn),并能夠結(jié)合具體案例分析工業(yè)化進(jìn)程對城市化的巨大推動。 4、分析珠江三角洲地區(qū)工業(yè)化和城市化進(jìn)程中的問題,并嘗試評價目前的一些調(diào)整措施和發(fā)展方向。5、通過分析我國珠江三角 洲地區(qū)工 業(yè)化、城市化的發(fā)展階段、問題與對策,了解區(qū)域工業(yè)化和城市化的推進(jìn)動力和發(fā)展規(guī)律。過程與方法 利用扮演不同的社會角色來談對珠江三角洲地區(qū)未來經(jīng)濟(jì)和城鎮(zhèn)發(fā)展的設(shè)想和建議,反饋學(xué)生知識、能力、價值觀發(fā)展情況和效果, 培養(yǎng)學(xué)生對所學(xué)所得的運(yùn)用能力,并為學(xué)生的創(chuàng)新精神的發(fā) 展?fàn)I造有利氛圍。情感、態(tài)度與價值觀1、通過鼓勵學(xué)生主動獲 取資料的做法,關(guān)注學(xué)生實(shí)踐能力、綜合思維能力及終身學(xué)習(xí)能力的訓(xùn)練。

This unit is about the Internet, which has a great influence to our humans and our lives. During the Listening & Speaking & Talking and Reading and Thinking section, the influence in examples has been shown. Thus, use the Present Perfect Tense is appropriate. However, in order to show the justice or weaken the doer of the behavior/action, it’s better to use the Present Perfect Passive Voice than the Present Perfect Tense. Besides, having learned to use the Present Perfect Passive Voice, students can beautify their language in their writing. 1. Learn the structure of the Present Perfect Passive Voice and its functions. 2. Learn to change the sentences with the Present Perfect Passive Voice into the sentences with the Present Perfect Passive Voice. 3. Learn to write sentences with the Present Perfect Passive Voice flexibly according to the context. 1. Learn the structure of the Present Perfect Passive Voice and its functions. 2. Learn to change the sentences with the Present Perfect Passive Voice into the sentences with the Present Perfect Passive Voice. 3. Learn to write sentences with the Present Perfect Passive Voice flexibly according to the context. Step 1 Observe the following sentences, then change the sentences into passive voice.He has been selected to take part in the sports meeting.(肯定句)他已被挑選出來參加運(yùn)動會。The ink has not been removed from his overcoat.(否定句)墨跡還沒有從他外套上去掉。

【點(diǎn)津】 1.不定式的復(fù)合結(jié)構(gòu)作目的狀語 ,當(dāng)不定式或不定式短語有自己的執(zhí)行者時,要用不定式的復(fù)合結(jié)構(gòu)?即在不定式或不定式短語之前加 for +名詞或賓格代詞?作狀語。He opened the door for the children to come in. 他開門讓孩子們進(jìn)來。目的狀語從句與不定式的轉(zhuǎn)換 英語中的目的狀語從句,還可以變?yōu)椴欢ㄊ交虿欢ㄊ蕉陶Z作狀語,從而使句子在結(jié)構(gòu)上得以簡化。可分為兩種情況: 1?當(dāng)目的狀語從句中的主語與主句中的主語相同時,可以直接簡化為不定式或不定式短語作狀語。We'll start early in order that/so that we may arrive in time. →We'll start early in order to/so as to arrive in time. 2?當(dāng)目的狀語從句中的主語與主句中的主語不相同時,要用動詞不定式的復(fù)合結(jié)構(gòu)作狀語。I came early in order that you might read my report before the meeting. →I came early in order for you to read my report before the meeting.

一、教材內(nèi)容經(jīng)全國中小學(xué)教材審定委員會2004年初審查通過,人教育出版社出版的普通高中課程標(biāo)準(zhǔn)實(shí)驗(yàn)教科書《物理必修①》,第三章第5節(jié)內(nèi)容“力的分解”。二、教學(xué)目標(biāo)1.知識與技能(1)理解分力的概念,理解力的分解是力的合成的逆運(yùn)算,遵循平行四邊形定則。(2)初步掌握一般情況下力的分解要根據(jù)實(shí)際需要來確定分力的方向。(3)會用作圖法和直角三角形的知識求分力。(4)能區(qū)別矢量和標(biāo)量,知道三角形定則,了解三角形定則與平行四邊形定則的實(shí)質(zhì)是一樣的。2.過程與方法(1)進(jìn)一步領(lǐng)會“等效替代”的思想方法。(2)通過探究嘗試發(fā)現(xiàn)問題、探索問題、解決問題能力。(3)掌握應(yīng)用數(shù)學(xué)知識解決物理問題的能力。3.情感態(tài)度與價值觀(1)通過猜測與探究享受成功的快樂。(2)感受物理就在身邊,有將物理知識應(yīng)用于生活和生產(chǎn)實(shí)驗(yàn)的意識。三、教學(xué)重點(diǎn)、難點(diǎn)在具體問題中如何根據(jù)力的實(shí)際作用效果和平行四邊形定則進(jìn)行力的分解。

一般情況下,凡是支持物對物體的支持力,都是支持物因發(fā)生形變而對物體產(chǎn)生彈力。所以支持力的方向總是垂直于支持面而指向被支持的物體。例1:放在水平桌面上的書書由于重力的作用而壓迫桌面,使書和桌面同時發(fā)生微小形變,要恢復(fù)原狀,對桌面產(chǎn)生垂直于桌面向下的彈力f1,這就是書對桌面的壓力;桌面由于發(fā)生微小的形變,對書產(chǎn)生垂直于書面向上的彈力f2,這就是桌面對書的支持力。學(xué)生分析:靜止地放在傾斜木板上的書,書對木板的壓力和木板對書的支持力。并畫出力的示意圖。結(jié)論:壓力、支持力都是彈力。壓力的方向總是垂直于支持面而指向被壓的物體,支持力的方向總是垂直于支持面而指向被支持的物體。引導(dǎo)學(xué)生分析靜止時,懸繩對重物的拉力及方向。引導(dǎo)得出:懸掛物由于重力的作用而拉緊懸繩,使重物、懸繩同時發(fā)生微小的形變。重物由于發(fā)生微小的形變,對懸繩產(chǎn)生豎直向下的彈力f1,這是物對繩的拉力;懸繩由于發(fā)生微小形變,對物產(chǎn)生豎直向上的彈力f2,這就是繩對物體的拉力。

l.知識與技能:(1)知道摩擦力產(chǎn)生的條件。(2)能在簡單問題中,根據(jù)物體的運(yùn)動狀態(tài),判斷靜摩擦力的有無、大小和方向;知道存在著最大靜摩擦力。(3)掌握動磨擦因數(shù),會在具體問題中計(jì)算滑動磨擦力,掌握判定摩擦力方向的方法。(4)知道影響到摩擦因數(shù)的因素。2.過程與方法:通過觀察演示實(shí)驗(yàn),概括出摩擦力產(chǎn)生的條件及摩擦力的特點(diǎn),培養(yǎng)學(xué)生的觀察、概括能力。通過靜摩擦力與滑動摩擦力的區(qū)別對比,培養(yǎng)學(xué)生分析綜合能力。3.情感態(tài)度價值觀:在分析物體所受摩擦力時,突出主要矛盾,忽略次要因素及無關(guān)因素,總結(jié)出摩擦力產(chǎn)生的條件和規(guī)律。二、重點(diǎn)、難點(diǎn)分析1.本節(jié)課的內(nèi)容分滑動摩擦力和靜摩擦力兩部分。重點(diǎn)是摩擦力產(chǎn)生的條件、特性和規(guī)律,通過演示實(shí)驗(yàn)得出關(guān)系f=μN(yùn)。2.難點(diǎn)是學(xué)生有初中的知識,往往誤認(rèn)為壓力N的大小總是跟滑動物體所受的重力相等,因此必須指出只有當(dāng)兩物體的接觸面垂直,物體在水平拉力作用下,沿水平面滑動時,壓力N的大小才跟物體所受的重力相等。

1.用CAI課件模擬汽車的啟動過程。師生共同討論:①如果作用在物體上的力為恒力,且物體以勻速運(yùn)動,則力對物體做功的功率保持不變。此情況下,任意一段時間內(nèi)的平均功率與任一瞬時的瞬時功率都是相同的。②很多動力機(jī)器通常有一個額定功率,且通常使其在額定功率狀態(tài)工作(如汽車),根據(jù)P=FV可知:當(dāng)路面阻力較小時,牽引力也小,速度大,即汽車可以跑得快些;當(dāng)路面阻力較大,或爬坡時,需要比較大的牽引力,速度必須小。這就是爬坡時汽車換低速擋的道理。③如果動力機(jī)器在實(shí)際功率小于額定功率的條件下工作,例如汽車剛剛起動后的一段時間內(nèi),速度逐漸增大過程中,牽引力仍可增大,即F和v可以同時增大,但是這一情況應(yīng)以二者乘積等于額定功率為限度,即當(dāng)實(shí)際功率大于額定功率以后,這種情況不可能實(shí)現(xiàn)。
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