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人教版新課標高中物理必修2能量守恒定律與能源說課稿3篇
（3）內(nèi)陸和中西部城鎮(zhèn)主要以煤和火電為主；廣大農(nóng)村和邊遠地區(qū)大多正從使用農(nóng)作物秸稈等生物能源。（4）人均能源資源不足。我國是世界第三大能源生產(chǎn)國和第二大能源消費國，而我國能源短缺，特別是油氣資源短缺已成為制約我國經(jīng)濟發(fā)展的重要因素。相關數(shù)據(jù)——煤炭、石油和天然氣的人均資源占有量只有95t，世界平均值為209t，約是世界人均值的1/2；我國人均石油可采儲量3t，世界平均值為28t，約為世界平均值的1/10。我國人均能源消費量不足1.2噸標準煤，居世界89位，不足世界人均能源消費水平的一半，僅占發(fā)達國家的1/5～1/10。其中人均消費650kg標準煤，是世界平均額的95%；人均消費石油相當145kg標準煤，為世界平均數(shù)的16.8%；人均消費天然氣相當17.7kg標準煤，為世界平均數(shù)的3.9%；人均消費電力501.5kWh，為世界平均水平的25%。（5）是能源消費結構不合理，突出存在著一低兩高：即電能消費比例低，非商品生物能源消費量高，一次性商品能源消費中原煤消費比重高。原煤消費達到75%，遠高于26.2%的世界平均水平。
人教版新課標高中物理必修1自由落體運動說課稿2篇
學生回答的方法多樣，讓各小組根據(jù)自己討論出來的方法對自己實驗出來的紙帶進行數(shù)據(jù)處理，并求出加速度，并且將多條紙帶都進行處理，同時提醒學生對紙帶的選擇。接著，我會用多媒體展示重物下落實驗打出來的紙帶，用表格列出一段紙帶上各點的瞬時速度，準確畫出v-t圖像，求出加速度，將結果給予學生的結果作對比，確定出正確結論。最后讓學生分析總結：自由落體運動是初速度為零的勻加速直線運動，而且，多條紙帶算出來的加速度的數(shù)值都接近相等，即加速度在實驗誤差允許范圍內(nèi)是相等的。引出重力加速度，介紹概念、方向及大小。（強調(diào)“同一地點”，讓學生閱讀教材中一些地點的重力加速度，可以了解重力加速度的大小與緯度有關，緯度越大加速度越大）。學習了重力加速度后讓學生根據(jù)之前學習的勻變速直線運動公式推導出自由落體的運動規(guī)律。設計意圖：讓學生在學習過程中的主體地位和自主觀能動性得到充分發(fā)揮，取長補短，培養(yǎng)了學生的實驗操作能力，又使學生對自由落體運動的性質(zhì)有深刻的印象，從而解決了本節(jié)課第二個難點。
人教版新課標高中物理必修1時間和位移說課稿2篇
研究一種物理現(xiàn)象，總是要先從現(xiàn)象的描述入手。機械運動作為自然界最簡單和最基本的運動形態(tài)，它所描述的是物體空間位置隨時間變化的情況。因此，本節(jié)學習描述質(zhì)點做機械運動需要時刻、時間間隔和位移等概念。相當一部分高一學生在具體過程中難以區(qū)別時刻和時間間隔。另外，由于思維的定式，在第一次接觸既要考慮大小又要考慮方向的問題時，會因不適應造成學習困難。所以，區(qū)別“路程與位移”“時刻和時間間隔”是教學的重難點所在。學習這些內(nèi)容的過程與方法對學習速度和加速度可以起到奠定基礎的作用。教學的對象是高一的學生，這一時期的學生處在好奇善問、創(chuàng)新意識強烈的青少年期。對于生活中出現(xiàn)的各種現(xiàn)象具有濃厚的興趣。但他們的思維還停留在簡單的代數(shù)運算階段，對于矢量和矢量運算的理性認識幾乎沒有。且對生活中出現(xiàn)的時間、時刻、時間間隔等不能做出很好的區(qū)分，對時常提及的路程、距離等形成了模糊的前概念。
人教版新課標高中物理必修1質(zhì)點參考系和坐標系說課稿2篇
一、說教材《質(zhì)點 參考系和坐標系》是人教版普通高中物理必修一第一章第一課的內(nèi)容。本節(jié)課主要介紹了質(zhì)點、參考系、坐標系的基本概念。通過本節(jié)課的學習為進一步學習后續(xù)課程起到了鋪墊的作用。根據(jù)上述教材的結構和內(nèi)容分析，又考慮到高一年級學生的認知結構及其心理特征，我制定了以下三維教學目標：1、知識與技能：知道質(zhì)點的概念及條件；知道參考系的概念及作用；掌握坐標系的簡單應用。2、過程與方法：促進學生自主學習，讓學生積極參與、樂于探究、勇于實驗、勤于思考，培養(yǎng)學生的科學探究能力。3、情感態(tài)度與價值觀：通過質(zhì)點 參考系和坐標系的學習，使學生了解生活與物理的關系，讓學生學會用科學的思維去看待事物。根據(jù)普通高中物理課程標準，并在吃透教材的基礎上，我確定了以下教學重點和難點：教學重點：質(zhì)點概念的建立。只有掌握了這一點才能更加準確的理解和掌握后續(xù)教材的相關內(nèi)容。
人教版新課標高中物理必修2動能和動能定理說課稿3篇
2、教學目標根據(jù)我對教材的理解、結合學生的實際情況、滲透新課程的教學理念，為提高全體學生的科學素養(yǎng)，按課程標準，以促進全體學生發(fā)展為目的。從知識與技能、過程與方法，情感態(tài)度與價值觀三個方向培養(yǎng)學生，擬定三個教學目標：知識與技能：（1）知道什么是動能。（2）正確理解和運用動能公式分析、解答有關問題。（3）掌握外力對物體所做的總功的計算，理解“代數(shù)和”的含義。（4）理解和運用動能定理。過程與方法：通過演繹推理過程，培養(yǎng)科學研究興趣，領略物理學中所蘊含的嚴謹?shù)倪壿嬯P系。情感、態(tài)度、價值觀：通過運用動能定理分析解決問題，感受成功的喜悅，培養(yǎng)學生對科學研究的興趣。3、教學的重點和難點重點：理解動能定理、應用動能定理解決力學問題。難點：應用動能定理解決多個過程的力學問題，以及變力做功或曲線運動中的動能定理運用。
人教版新課標高中物理必修2圓周運動說課稿3篇
設計意圖：通過設疑、討論及學生的親身體驗與教師的引導，得到描述圓周運動快慢的兩個物理量，也就成功的打破了學生在認識上的思維障礙，突破了物理概念教學的難點。在解決線速度和角速度的問題之后，我將引領學生學習勻速圓周運動的概念以及勻速圓周運動中線速度、角速度的特點。并引出勻速圓周運動中周期、轉速的知識。為了加深學生對線速度、角速度與半徑關系的認識，我設計了第三個學生體驗活動：四名學生以我為圓心做圓周運動，四名學生始終并列，這時里圈同學走動不急不慢，而外圈同學則要小跑。通過學生的活動，不難發(fā)現(xiàn)在角速度相同的情況下，半徑越大的線速度也越大。定性的得到了線速度、角速度與半徑的關系。接下來讓學生利用所學知識推導線速度、角速度與半徑的關系。設計意圖：這樣就通過設疑、學生猜想、體驗、推導的方式得到了結論，突破了本節(jié)課的難點即線速度、角速度與半徑的關系。
人教版高中歷史必修3從“師夷長技”到維新變法說課稿2篇
(一)、教材地位：我說課的內(nèi)容是人教版高二歷史（必修3）第五單元《從“師夷長技”到維新變法》。本課主要講述了鴉片戰(zhàn)爭后中國思想界發(fā)生的巨大變化，所講述內(nèi)容對中國近百年的歷史走向，對近代中國政治發(fā)展所產(chǎn)生的影響是至關重要的，所以這節(jié)課在教材中具有重要的地位和作用，同時也是本冊書中的重要章節(jié)。(二)、課標要求：《高中歷史新課程標準》對這一節(jié)內(nèi)容作了這樣的要求：了解鴉片戰(zhàn)爭以后中國人學習西方 尋求變革的思想歷程，理解維新變法思想在近代中國社會發(fā)展中所起的作用。(三)、教學目標：根據(jù)課標要求、教材內(nèi)容和學生的具體情況，確立以下教學目標：1、知識與能力：（1）識記：林則徐被稱為“開演看世界的第一人”；魏源的“師夷長技以制夷”思想；洋務派“師夷長技以自強”思想；早期維新思想和90年代維新思想；
人教版高中歷史必修3從蒸汽機到互聯(lián)網(wǎng)說課稿2篇
2、互聯(lián)網(wǎng)的功用：（1）功用：提供文件傳輸、電子信箱、聊天等服務，在社會各個領域發(fā)揮了巨大的作用，標志著信息化社會的出現(xiàn)。（2）特點：網(wǎng)絡媒體作為一種新的傳播媒體，具有界面直觀、音色兼?zhèn)?、鏈接靈活和高速傳輸?shù)奶攸c。3、互聯(lián)網(wǎng)的影響：教師提問，學生思考回答，教師總結 （1）信息經(jīng)濟在世界各地全面發(fā)展，加快了經(jīng)濟全球化的步伐；（2）傳統(tǒng)產(chǎn)業(yè)也借助互聯(lián)網(wǎng)提高管理水平，并通過全球營銷和采購擴大市場；（3）在互聯(lián)網(wǎng)時代，人們可以在家里完成很多工作，提高了工作效率，增加了樂趣；（4）人們的社會交往方式也發(fā)生著改變。（5）也帶來一些負面影響?！竞献魈骄俊?:青少年如何對待網(wǎng)絡：互聯(lián)網(wǎng)在給社會帶來巨大效能的同時，也帶來了巨大的挑戰(zhàn)。青少年應該提高自身的道德素養(yǎng)，樹立正確的網(wǎng)絡觀，讓網(wǎng)絡發(fā)揮出應有的作用。
人教版高中歷史必修3音樂與影視藝術說課稿2篇
一、教材地位《音樂與影視藝術》是人教版高中歷史必修（III）第八專題中的第三節(jié)內(nèi)容。音樂、影視藝術屬于意識形態(tài)范疇，是當時政治、經(jīng)濟的反映，是社會進步的產(chǎn)物。19世紀以來的音樂與影視藝術糅合了近代科學技術的元素,直接引領著文明發(fā)展趨勢和社會風尚，滿足人們不同層次的審美需要和精神追求。音樂、影視藝術在人類日常生活中無處不在，已經(jīng)成為人們?nèi)粘Ｉ钪械闹匾M成部分,所以具有重要地位。本課分三個部分介紹了19世紀和20世紀音樂的發(fā)展與變化以及影視藝術的產(chǎn)生發(fā)展。下面我就談談對這節(jié)課的教學思路。二、教材分析1、課標要求課標的要求是：列舉19世紀以來有代表性的音樂作品，理解這些音樂作品的時代性和民族性。了解影視藝術產(chǎn)生與發(fā)展的歷程，認識其對社會生活的影響。2、教學目標根據(jù)新課標、教材內(nèi)容、學生實際，確定教學目標如下：（1）知識與能力：①列舉19世紀以來有代表性的音樂作品，理解這些音樂作品的時代性和民族性。
人教版高中歷史必修3破解生命起源之謎說課稿2篇
過度：誠如牛頓所說 我之所以能夠取得今天的成就有很大原因是站在巨人的肩膀之上設問3：為什么這個時代選擇了達爾文來完成這一偉大的發(fā)現(xiàn)呢？（達爾文的個人努力）補充材料：（1831年起，他隨“貝格爾號”考察艦進行環(huán)球考察5年?？疾旖Y束后，在整理考察資料和實物標本的基礎上，經(jīng)過長期的研究，于1859年出版了《物種起源》一書，確立了生物的進化論說明達爾文的個人努力：學習、考察、學習、不迷信權威、勇于挑戰(zhàn)、不斷探索的精神，飽覽群書，挑戰(zhàn)和假設建立在大量的閱讀和觀察的基礎上，科學實證等等?？梢哉f達爾文身上有那個時代的一個濃縮的特征，當然他還有點運氣，不過，機遇永遠是為那些有準備的人提供的。）探究：達爾文“進化論”的影響思路引領：科學理論發(fā)展的影響可以從哪些方面分析？（經(jīng)濟、科學理論本身、人文學科、社會影響（對宗教，社會），對其他國家的影響）設問：達爾文進化論對1859年及以后的社會帶來了非常深遠的影響。有哪些影響呢？①挑戰(zhàn)封建神學的神創(chuàng)世，促進人類認識的飛躍
人教版高中政治必修3加強思想道德建設說課稿2篇
師：建立社會主義思想道德體系，必須牢固樹立社會主義榮辱觀。在我們的社會主義社會里，是非、善惡、美丑的界限絕對不能混淆，堅持什么、反對什么，倡導什么、抵制什么，都必須旗幟鮮明。我們堅持以熱愛祖國為榮、以危害祖國為恥，以服務人民為榮、以背離人民為恥，以崇尚科學為榮、以愚昧無知為恥，以辛勤勞動為榮、以好逸惡勞為恥，以團結互助為榮、以損人利己為恥，以誠實守信為榮、以見利忘義為恥，以遵紀守法為榮、以違法亂紀為恥，以艱苦奮斗為榮、以驕奢淫逸為恥。課堂小結通過本節(jié)課學習，使我們認識到中國特色社會主義文化建設的中心環(huán)節(jié)是思想道德建設，了解什么是社會主義思想道德，為什么要建設社會主義思想道德體系和怎樣建設社會主義思想道德體系，大力倡導“愛國守法、明禮誠信、團結友善、勤儉自強、敬業(yè)奉獻”的基本道德規(guī)范。我們要大力加強社會主義思想道德建設，為社會主義各項事業(yè)的發(fā)展提供強大的精神動力和方向保證。
新人教版高中英語必修2Unit 2 Wildlife Protection-Reading for Writing教案二
This lesson aims at making a poster about protecting wildlife after reading some posters. During reading students are guided to understand the content and try to summarize the posters with one sentence. Then students are guided to try to make a poster about protecting wildlife.1. Read the two posters and try to understand the summary sentences.2. Look at the two posters and try to understand what emotions they express.3. Try to summarize the features of posters4. Try to make a poster about wildlife.1. Look at the two posters and try to understand what emotions they express.2. Try to summarize the features of posters3. Try to make a poster about wildlife.Step 1 Lead inLook at the the posters on the textbook and ask:Which emotions do the posters communicate ?Step 2 Read the poster and answer the questions.1. What do you think of the animals in the poster on the left ?I think it is frightening and ugly.2. Why do we should protect the ugly animals ?All species--the good, the bad, and the ugly-- should be treated equally.The world needs all kinds--without variety, our planet cannot survive.3. Why are billions of trees being cut down every year ?To make paper for humans.4. What result will be lead to after the trees are cut down ?A lost of animal homes are being destroyed./The habitat of wildlife is being destroyed.Step 3 Find the feature of posters1. What does each poster use to stir up emotions ?On the left, it makes us a little frightened and it looks a little ugly, but it can activate our curiosity--What is it? And What is wrong with it?On the right, it makes us feel a little sad and want to protect them.
新人教版高中英語必修2Unit 2 Wildlife Protection-Discovering Useful Structure教案二
2．表示現(xiàn)階段正在進行的被動動作(該動作在說話的瞬間未必正在進行)。Many interesting experiments are being carried out these days.(說話時，并不一定正在進行)3．表示一種經(jīng)常性的被動行為，常和always，constantly 等表示頻度的副詞連用，這種用法常常帶有贊揚或厭惡的感情色彩。He is always being praised by the leader.4．表示按計劃或安排主語將要承受謂語動詞所表示的動作(僅限于少數(shù)及物動詞)。A party is being held tonight.Step 4 Special cases1.像take care of, look after, talk about, think of等動詞與介詞構成的短語用于現(xiàn)在進行時的被動語態(tài)時, 其中的介詞不可省略。The ways to stop illegally hunting are being talked about. 2．可與部分情態(tài)動詞連用，表示對正在發(fā)生的事情的推測。She may be being punished by her mother.3．有時可表示按計劃或安排將要進行的一個被動動作。A celebration is being held this weekend for his success.4．某些表示“狀態(tài)、心理活動、存在”等的動詞，如have，want，need，love，一般不用現(xiàn)在進行時的被動語態(tài)，而常用一般現(xiàn)在時的被動語態(tài)。With the population increasing，more land is needed.5．“be＋under/in＋n.”可表示現(xiàn)在進行時的被動意義。My computer is under repair.＝My computer is being repaired.
新人教版高中英語必修2Unit 2 Wildlife Protection-Discovering Useful Structure教案一
The activity topic of this section is "report an ongoing event", and the structure is the passive voice of present continuous tense. Rare wild animals are suffering from large-scale poaching, and species are on the brink of danger. Rescue operations are underway. "Being" and "suffering" are the meanings of the present progressive passive voice.The usage of present progressive passive voice is of great importance in writing a good discourse and appreciating some difficult language items, so it is vital to master it and use it flexibly in a context.1. Motivate Ss to deepen the understanding of the usage of present progressive passive voice in a fixed context.2. Enable Ss to master the usage of present progressive passive voice and use it flexibly in a context.3. Lead Ss to construct sentences or appreciate sentences used master it and use it flexibly in a context.1. Help students to appreciate the function of the usage of present progressive passive voice in a sentence2. Instruct students to write essays using the proper usage of present progressive passive voice.Look at the picture and tell me what are workers doing? What is the house being done?
新人教版高中英語必修2Unit 2 Wildlife Protection-Reading and Thinking教案一
The listening and speaking part aims at how to protect and help endangered animals by listening, speaking and talking about the facts and reasons. This lesson analyzes the decreasing clause of Tibetan antelope population and the measures of protecting Tibetan antelopes. So students can be guided to learn to analyse the title and use different reading skills or strategies, like scanning, skimming and careful reading.1. Read quickly to get the main ideas and the purpose of going to Tibetan; read carefully to understand what the author see and think.2. Understand the sentences of the present continuous passive voice such as “Much is being done to protect wildlife.” and the inverted sentence “Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.”3. Enhance the awareness of protecting wildlife.4. Cultivate the reading methods according to different materials.1. Read quickly to get the main ideas and the purpose of going to Tibetan; read carefully to understand what the author see and think.2. Understand the sentences of the present continuous passive voice such as “Much is being done to protect wildlife.” and the inverted sentence “Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.”3. Cultivate the reading methods according to different materials.Step 1 Leading-inWatch a video about elephants and whales and then ask:Why are they endangered ? They are killed/hunted
新人教版高中英語必修2Unit 2 Wildlife Protection-Listening &Speaking＆Talking教案
Listening and Speaking introduces the topic of “how to save endangered wildlife and help wildlife in their neighborhood.” Due to the continuous deterioration of the living environment, a large number of wild animals are always facing the threat of endangered or extinction. Listening and speaking period enables students to understand the fact and reason why wild species are disappearing from the earth at an amazing speed, and realize that human beings ought to enhance the awareness of protecting wild species as soon as possible.Listening and Talking introduces the theme of " how to help wildlife in Ss’ neighborhood.". Now there are many volunteers who spontaneously protect wild animals, carry out various activities according to local conditions, and contribute their own strength to local animal protection with practical actions. Middle school students are also enthusiastic participants. They organize activities in their spare time, and take this opportunity to make friends, broaden their horizons, cultivate team spirit and communication skills. This section describes a bird watching activity organized by several middle school students of Bird watching Club. It aims to stimulate students' interest, improve their understanding of bird watching activities, and use the language structure of “being used for; in order to, so as to, to, so that, in order that ” to express the purpose for communication and discussion.1. Guide students to understand the content of listening texts in terms of using visuals to predict content.2. Cultivate students' ability to guess the meaning of words in listening; discuss with their peers how to save endangered wildlife and help wildlife in their neighborhood.3. Instruct students to use functional sentences of the dialogue such as “I am concerned about…” “what do you know about the endangered animals in…" and so on to talk about one of the endangered animals.
新人教版高中英語必修2Unit 2 Wildlife Protection-Listening and Speaking教案
This lesson is about wildlife protection. The listening and speaking is about “How to protect endangered wildlife ?” Faced with the facts and numbers of wildlife loss, people begin to detect the reasons, then people such as the celebrities (Prince William and Yao Ming) are calling on to protect them. So students are guided to enhance the awareness of protecting wildlife and try to take part in some volunteer activities of protecting wildlife.1. Predict the content by using visuals. 2. Learn to use the sentences such as “I’m concerned about.... But now they are in danger. I want to know the reasons/why./ What can we do to protect them ?3. Learn from the stars like Prince William and Yao Ming and enhance the awareness of protecting wildlife.4. Guide students to try to put forward the solutions to the problems of wildlife protection and then discuss them with partners and present the results of discussion.5. Master the pronunciation of stressed syllables.1. Learn from the stars like Prince William and Yao Ming and enhance the awareness of protecting wildlife.2. Guide students to try to put forward the solutions to the problems of wildlife protection and then discuss them with partners and present the results of discussion.3. Learn to use the sentences such as “I’m concerned about.... But now they are in danger. I want to know the reasons/why./ What can we do to protect them ?4. Master the pronunciation of stressed syllables.Part A Listening and Speaking--- How to save endangered wildlifeStep 1 Lead in1. Point at the pictures on P14 and ask Q1: What message do these posters share?
新人教版高中英語必修2Unit 2 Wildlife Protection-Reading and Thinking教案二
The theme of this unit is human and nature, focusing on the theme of wildlife protection. Nature is a complex ecosystem, in which there are delicate balance between animals and plants. Because of the role of the food chain, the extinction of one species will produce influence, causing a series of chain reaction. Large scale extinction of species will have a serious and even irreversible impact on the ecosystem, resulting in immeasurable losses. Therefore, it is of great significance to protect wild species. To protect wild species is to protect human beings themselves. The motto of this unit is "when the buying stops, the killing can too,” which is a public service advertising slogan to protect wildlife. It tells people that every rhinoceros horn, every fur, every bowl of shark fin soup, every Ivory product, and every tiger bone product, etc. consumed by human beings, are innocent wild animals slaughtered behind them. The mission of wild aid is to ban illegal trade in endangered wildlife and mitigate climate change. It aims to educate the public to reduce the consumption demand for endangered wildlife products through public publicity and improve the awareness of environmental protection.1. Improve the awareness of wildlife protection by acquiring the knowledge of wildlife protection.2. Focus on environmental protection and protection of all lives.3. Analysis of the living environment of wild animals with appropriate thinking mode.4. Skillfully use the vocabulary and grammar knowledge of this unit to cultivate self-study ability according to the unit content5. Develop cooperative learning ability through discussion and other ways1. Enable the Ss to talk about the current situation of wild animals.2. Guide the Ss to summarize the main idea of each paragraph as well as the main idea of the text.
新人教版高中英語必修2Unit 2 Wildlife Protection-Reading For Writing教案一
1. 標題首先根據(jù)海報的特點、格式寫明標題。海報中往往把內(nèi)容作為大標題。例如: Save the earth, Save the birds。2. 正文部分不同的海報其正文部分的側重點不同。對于介紹性的海報, 首先要引出話題, 其次列出原因, 最后是總結。對于宣傳類的海報, 要寫明具體內(nèi)容, 如: 活動內(nèi)容, 地點以及參加活動的注意事項, 主持或舉辦單位等。1. 圖片: 要選擇引人注目的圖片, 與主題要相關, 色彩明亮。話題句式 1. It is a treasure of our country. 它是我國的國寶。2. Believe it or not, at present only several thousand pandas exist in the world. 信不信由你, 目前世界上僅現(xiàn)存幾千只熊貓。 3.It’s because of human activities that tigers are endangered. 正是因為人類的活動, 老虎處于瀕危的狀態(tài)。4. Many wild animals are in danger of dying out. 很多野生動物面臨著滅絕的危險。 5. The government has taken effective measures to protect them. 政府已采取有效的措施來保護它們。6. People should raise the awareness of the protection of wild animals. 人們應該提高保護野生動物的意識。 7. It’s amazing that there are merely less than 1, 000 finless porpoises living in China. 非常令人吃驚, 目前中國僅有不足1 000只江豚。
人教版新課標高中物理必修2功率教案2篇
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，但是這一情況應以二者乘積等于額定功率為限度，即當實際功率大于額定功率以后，這種情況不可能實現(xiàn)。