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為關(guān)心她的命運,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??梢哉f,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。
(2)根據(jù)材料二與所學(xué)知識,從經(jīng)濟(jì)、政治、思想文化三個方面,分析歐洲近代科技迅速發(fā)展的原因。答:資本主義工商業(yè)的成長刺激了對技術(shù)的需求,為近代科技的發(fā)展提供了工具和手段;資產(chǎn)階級革命為資本主義發(fā)展、科技進(jìn)步開辟了道路;人文主義和理性精神解放了思想,推動近代科技迅速發(fā)展。(如答出其它原因,言之有理,可酌情加分,但不得超過該問總分)(3)根據(jù)材料二三與所學(xué)知識,分析清代(鴉片戰(zhàn)爭前)中國科技發(fā)展停滯的原因。答:君主專制維系腐朽制度;重農(nóng)抑商、閉關(guān)政策阻礙資本主義萌芽發(fā)展;自然經(jīng)濟(jì)不能提供近代科技發(fā)展的物質(zhì)基礎(chǔ);文化專制政策(或崇尚理學(xué)、八股取士、文字獄等)禁錮思想,摧殘人才,阻礙科技發(fā)展。(如答出其它原因,言之有理,可酌情加分,但不得超過該問總分。)(4)簡述從中西方科技發(fā)展變化的歷史中得到的啟示。答:評分說明:圍繞生產(chǎn)力發(fā)展,政治經(jīng)濟(jì)變革、思想解放與科技發(fā)展的關(guān)系等任一角度回答,言之有理,均可酌情賦分
三、第三階段。課后感悟與收獲1、讓學(xué)生以“走向?qū)W習(xí)型社會”為題,將在收集與整理、展示與交流兩個環(huán)節(jié)中獲得的體驗和感悟,以心得體會的形式寫一篇小論文。2、辦一期專欄或黑板報,將優(yōu)秀小論文作集中展示與交流。(進(jìn)行理論總結(jié),將實踐與理論相結(jié)合,讓科學(xué)理論更好地指導(dǎo)實踐。充分挖掘?qū)W生潛力,增強學(xué)生的自信)[評析]新課程理念之一就是政治課不應(yīng)只局限于課堂上的教與學(xué)。把綜合探究課與研究性學(xué)習(xí)相結(jié)合,不失為一種有益的嘗試。傳統(tǒng)的學(xué)習(xí)方式把學(xué)習(xí)建立在客觀性、受動性、依賴性的基礎(chǔ)上,把學(xué)生看成一個沒有感情的接受容器,這種學(xué)習(xí)會窒息學(xué)生的思維和智力,成為學(xué)生發(fā)展的障礙。單元探究活動的開展就是要轉(zhuǎn)變學(xué)生的學(xué)習(xí)方式,關(guān)注學(xué)生的學(xué)習(xí)過程,使得探究過程成為學(xué)生發(fā)現(xiàn)問題、提出問題、分析問題、解決問題的過程,培養(yǎng)學(xué)生的創(chuàng)新精神和實踐能力。本教案的第一階段充分發(fā)揮了學(xué)生的主動性。
3、文化是人們的一種素養(yǎng)(1)人的文化素養(yǎng)是在社會生活、實踐中形成的。每個人所具有的文化素養(yǎng),不是天生的,而是通過對社會生活的體驗,特別是通過參與文化生活、接受知識文化教育而逐步培養(yǎng)出來的。文化素養(yǎng)的形成,離不開生活、實踐和教育。人們在社會實踐中創(chuàng)造和發(fā)展文化,也在社會生活中獲得和享用文化。(2)人的文化素養(yǎng)表現(xiàn)在日常言行中。教師活動:引導(dǎo)學(xué)生閱讀教材7頁“公交車漫畫”材料,并思考所反映的問題學(xué)生活動:積極思考并討論問題教師點評:人們的精神活動離不開物質(zhì)活動,人們的文化素養(yǎng)總是要通過他在日常生活中的言行、在社會實踐活動中的表現(xiàn)等表現(xiàn)出來。我們通過觀察人們的社會行為,就可以從中透視人們的精神世界和精神生活。4、文化的傳承和發(fā)展離不開物質(zhì)載體。社會文化和精神產(chǎn)品離不開物質(zhì)載體,一個時代的文化和精神產(chǎn)品,往往是這一時代社會發(fā)展軌跡的反映。
另一方面,文化素質(zhì)影響公民政治權(quán)利的行使。隨著民主和法制建設(shè)的發(fā)展,人們?yōu)榱藚⑴c政治生活,需要更高的文化素養(yǎng)。文化水平提高了,人們受到的教育、接受的信息就越多,活動的領(lǐng)域就越廣,民主法制和權(quán)利意識就越強,這些都會影響人們的民主素質(zhì)和民主水平,使人們更好地進(jìn)行政治參與,行使民主權(quán)利。(2)文化與國際政治相互交融,成為當(dāng)代國際政治斗爭的重要內(nèi)容。隨著世界多極化的發(fā)展,奉行霸權(quán)主義的國家,借助文化滲透的方式,竭力推銷自己的價值觀念,企圖削弱和取代別國的民族文化,以推行強權(quán)政治。這使世界范圍內(nèi)反對文化霸權(quán)主義的斗爭,成為當(dāng)代國際政治斗爭的重要內(nèi)容。文化已經(jīng)成為進(jìn)行政治斗爭、國際斗爭的重要形式之一。對文化市場的爭奪不僅僅是爭奪票房價值、爭奪經(jīng)濟(jì)效益,更主要的是對受眾對象的爭奪,對受眾注意力這種特殊的稀缺資源的占有,以及在此基礎(chǔ)上對輿論的控制與引導(dǎo)。因此,失去文化市場就意味著失去政治優(yōu)勢,意味著政治影響力的邊緣化乃至萎縮或喪失。這一點,從目前世界正在進(jìn)行的空前規(guī)模的“文化戰(zhàn)爭”,可以看得非常清楚。
2. Sort out detailed information about Michael Jordan.(1) Understand the transitional sentence.Q: Which part is about Michael Jordan as a master? Which part is about the example he set?(2) Have the Ss Focus on why Michael Jordan is a master and what good examples Michael Jordan set when they’re reading. And think about these questions as below:Q1: How does the author describe his impressive skills?Q2: How do you understand “time seemed to stand still”?Q3: What does “graceful” mean?Q4. Which sentence do you think best describes his mental strength?Q5. Which words is important in the sentence in describing his mental strength? Why?Q6: How do you understand “unique”?Q7: What can we learn from Michael Jordan?Step 5 Discussing and recommendingRecommend their own living legends of sports.Work in groups to choose your own living legend of sports and give the reasons of your choice. Step 6 HomeworkReview the stories of Lang Ping and Michael Jordan, and try to retell them.
Then have them write a short paragraph to describe and explain their changes. After that, get the Ss to exchange their drafts with their partners and use the checklist to give feedback on their drafts, and finally revise it.Step 5 Summary of how to write a wellness book1.健康書的審題步驟:第一步:明確要求該寫作屬于經(jīng)驗分享,故要用第一人稱來寫;時態(tài)以一股現(xiàn)在時為主。第二步:確定段落該類文章可以從以下三個方面人手:Para.1首先表明寫作的目的Para.2自己的做法及心得體會Para.3表示期望及感謝第三步:提煉要點2.健康書常見句式:1) It is an honor for me to share my favorite sport with you,2) It makes me feel relaxed playing with my friends.3) It makes me rid myself of stress while playing with my friends.4) Moreover, it provides me a valuable chance to communicate with others.5) I we eat too little or too much, or if we choose the wrong food, we may become sick.6) We can do something to change the poor situation.Step 6Homework假如你的老師讓你在班級Wellness Bok上分享自己的親身經(jīng)歷及心得,請根據(jù)以下要點寫一篇80字左右的文章1. 你喜歡的運動是什么?2. 你最喜歡的原因是什么?3. 你參加鍛煉的體會。
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,總結(jié)共同點。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?
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。
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.
Listening and Speaking introduces the topic of “ask about online habits”. Many middle school students have been surfing the Internet for many years, but what they do with the Internet and how much time they spend every day may not be very clear to themselves, nor to other students. This section allows students to investigate their peers' Internet use, which is conducive to their mutual understanding and understanding of the Internet. It can also help them reflect on their own online behavior, learn from other people's good online habits, and get rid of their bad online behavior.The listening text of this section is an investigation interview. The investigators interview specific groups with the same questions to obtain information, so as to understand their views, practices or attitudes on this issue. There are two specific questions: “how much time do you spend online every day? What do you usually do online?”. The answers of the three respondents provide rich and different information, and achieve the purpose of the investigators. The oral discourse structure of survey interviews generally includes greeting and explaining the purpose of the interview, presenting the interview questions and the respondents' answers. Listening and Talking introduces the theme of “choosing the right application ". Listening text is a conversation between Laura and Xiao Bo. In this part of listening, “oink”; “piggy bank” may cause the students' hearing comprehension limitation. Oink refers to sound word and pig's sound. So, add some oink to my piggy bank is often used to describe "making a little money".1. Guide students to understand the content of listening texts in terms of listening for definitions.2. Cultivate students' ability to define words and understand an investigation interview.
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.
Paragraph 3. Jan decided to start an IT club to teach old people how to use computers and the Internet. Paragraph 4. Jan has started taking online classes to learn more about how to use the Internet to make society better. Paragraph 5. Jan’s life has been greatly improved by the Internet. Step 5: Critical thinking:(1)How do you arrange your time spent on study and the Internet? Is it reasonable? I usually surf the Internet using my mobile phone for only an hour after class, and it is reasonable for me.(2)What are your online activities? Are they safe? I chat with my friends, read news and play games. I never give away my private information so I think they are safe.Step 4: summary Much has been written about the wonders of the World Wide Web. There are countless articles (1)______(tell) us how the Internet has made our lives more convenient. But the Internet has done a lot (2)_____(much) for people than simply make life more convenient. People’s lives (3) _________________(change) by online communities and social networks so far. Take Jan for example, who developed a serious illness that made her (4)_____(stick) at home with only her computer to keep (5)___(she) company. She joined an online group (6)______ 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)_______(benefit). She was so inspired (8)____ 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)___ children in poor countries. Jan’s life has been (10)______(great) improved by the Internet. Step 5 Homework:Review what we have learned and find out the key language points in the text.
⑦identity theft 身份盜竊⑧chat room 聊天室⑨draft your blog post 起草博客帖子⑩post embarrassing photos 張貼尷尬照片 【話題句式】 1. How do you stay safe online and avoid bad experiences on the Internet? 你如何在網(wǎng)上保持安全, 避免在網(wǎng)上的不良經(jīng)歷? 2. I’m not an expert, but many years as a blogger have taught me a thing or two. 我不是專家, 但作為一個博主, 我已經(jīng)學(xué)了好幾年了。 3. If you see or read something that makes you feel uncomfortable, leave the site immediately. 如果你看到或讀到一些讓你覺得不舒服的東西, 立即離開這個網(wǎng)站。4. Don’t give out your address or phone number. 別告訴別人你的地址或電話號碼。 5. Identity theft is a common and serious problem. 身份盜竊是一個常見而嚴(yán)重的問題。6. Being online is no excuse for being rude, and you don’t want to become a target for a troll or cyberbully. 上網(wǎng)并不是無禮的借口, 你也不想成為發(fā)挑釁帖子的人或網(wǎng)絡(luò)惡霸的目標(biāo)。 7. Trolls often use several false names so that they can stay on a site. 發(fā)挑釁帖子的人經(jīng)常使用幾個假名, 這樣他們就可以留在一個網(wǎng)站上。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。
在經(jīng)濟(jì)水平較高、工業(yè)地域規(guī)模較大的地區(qū),其發(fā)展?jié)摿瓦h(yuǎn)不一樣,如鋼鐵工業(yè)。鋼鐵工業(yè)的生產(chǎn)過程比較復(fù)雜(如課本圖5.31),需要有相互接近的工廠,不僅包括從事鋼鐵生產(chǎn)各道工序的工廠,如燒結(jié)廠、焦化廠、煉鐵廠、煉鋼廠、軋鋼廠,還包括與鋼鐵生產(chǎn)有聯(lián)系的工廠,如氧氣廠、機修廠、發(fā)電廠、水泥廠等,總共可達(dá)20~30個工廠。這些工廠集 聚,設(shè)備大,管線長,占地多。因此,這樣形成的工業(yè)地域(鋼鐵工業(yè)區(qū))面積廣,發(fā)育程度高,發(fā)展?jié)摿Υ?。這類工業(yè)地域 再加上為方便眾多工人生活所配置的服務(wù)業(yè)和其他工業(yè),在發(fā)展過程中,往往由于工業(yè)地域的擴展而形成工業(yè)城市。例如,我國的鞍山(“鋼都”)、攀枝花、馬鞍山、包頭(“草原鋼城”)等鋼鐵工業(yè)城市的形成。除此之外,石油化工區(qū)、機械制造工業(yè)區(qū)等屬于發(fā)育程度高的工業(yè)地域,也往往擴展而形成工業(yè)城市。例如,我國的石油城大慶、克拉瑪依,汽車城十堰等。
(五)平拋運動規(guī)律的應(yīng)用例1:一架老式飛機在高出海面45m的高處,以80m/s的速度水平飛行,為了使飛機上投下的炸彈落在停在海面上的敵船,應(yīng)該在與轟炸目標(biāo)的水平距離為多遠(yuǎn)的地方投彈?不計空氣阻力。分析:對于這道題我們可以從以下幾個方面來考慮:(1)從水平飛行的飛機上投下的炸彈,做什么運動?為什么?(2)炸彈的這種運動可分解為哪兩個什么樣的分運動?3)要想使炸彈投到指定的目標(biāo)處,你認(rèn)為炸彈落地前在水平方向通過的距離與投彈時飛機離目標(biāo)的水平距離之間有什么關(guān)系?拓展:1、式飛機在高出海面45m的高處,以80m/s的速度水平飛行,尾追一艘以15m/s逃逸的敵船,為了使飛機上投下的炸彈正好擊中敵船,應(yīng)該在與轟炸目標(biāo)的水平距離為多遠(yuǎn)的地方投彈?不計空氣阻力。2、在一次摩托車跨越壕溝的表演中,摩托車從壕溝的一側(cè)以速度v=40m/s沿水平方向向另一側(cè),壕溝兩側(cè)的高度及寬度如圖所示,摩托車可看做質(zhì)點,不計空氣阻力。(1)判斷摩托車能否跨越壕溝?請計算說明(2)若能跨過,求落地速度?
3.進(jìn)一步體會力是產(chǎn)生加速度的原因,并通過牛頓第二定律來理解勻速圓周運動、變速圓周運動及一般曲線運動的各自特點。(三)、情感、態(tài)度與價值觀1.在實驗中,培養(yǎng)學(xué)生動手、探究的習(xí)慣。2.體會實驗的意義,感受成功的快樂,激發(fā)學(xué)生探究問題的熱情、樂于學(xué)習(xí)的品質(zhì)。教學(xué)重點1.體會牛頓第二定律在向心力上的應(yīng)用。2.明確向心力的意義、作用、公式及其變形,并經(jīng)行計算。教學(xué)難點1.對向心力的理解及來源的尋找。2.運用向心力、向心加速度的知識解決圓周運動問題。教學(xué)過程(一)、 引入新課:復(fù)習(xí)提問:勻速圓周運動的物體的加速度——向心加速度,它的方向和大小有何特點呢?學(xué)生回答后進(jìn)一步引導(dǎo):那做勻速圓周運動物體的受力有什么特點呢?是什么力使物體做圓周運動而不沿直線飛出?請同學(xué)們先閱讀教材
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:通過觀察演示實驗,概括出摩擦力產(chǎn)生的條件及摩擦力的特點,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、難點分析1.本節(jié)課的內(nèi)容分滑動摩擦力和靜摩擦力兩部分。重點是摩擦力產(chǎn)生的條件、特性和規(guī)律,通過演示實驗得出關(guān)系f=μN。2.難點是學(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如果動力機器在實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)實際功率大于額定功率以后,這種情況不可能實現(xiàn)。