
This report is short, concise and has typical news content and language features. The title uses the verb phrases, embodying the characteristics of being concise and general. The introduction is the first two sentences in the first paragraph, describing the general situation of the cultural heritage protection project, including time, place, characters, events and other news elements, so that readers can see the main points of the news report at a glance. The main body is the second and third paragraphs, which report the important historical and cultural value of Mogao Grottoes and the production of Mogao Grottoes Material digital photos, which are of great significance to the inheritance of historical culture and the promotion of international cultural understanding, exchange and cooperation. Direct citation is used in the report, as well as background introduction and other news writing techniques.1. Get students to have a good understanding of some features about a news report by reading the text.2. Instruct students to write a summary about a news report properly using some newly acquired writing skills in this period.3. Develop students’ writing and cooperating abilities.4. Strengthen students’ great interest in writing discourses.1. Stimulate students to have a good understanding of how to a summary about a news report 2. Cultivate students to write a news report properly and concisely.Step 1: Lead in Do you think it is necessary for us to circulate our cultural heritage to the world? Why or why not?Do we need to learn more about other countries’ cultural heritage? Why or why not?Step 2: Read to discover details concerning the main body of the news report.

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.

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?

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.

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(cè)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(jié)。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(guān), 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(yīng)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。

Step 5 Practice一、完成下列句子。1. Judy and I _______________(把車停下來(park))in an underground car Park near Trafalgar Square, where we could ______________________(讓我們的車充電(charge)).2. When we finally reached the service desk to ask for audio guides, we heard it ___________ that there were no audio guides____________(留下,剩下).3. We__________________________(發(fā)現(xiàn)自己對...很驚訝)the large number of visitors and the amount of noise at the entrance of the National Gallery.4. Judy ____________________(眼神專注于) Van Gogh’s Sunflowers. It was hard to approach the painting as there were so many people around.5. She ____________________(把這幅畫的復(fù)制品裝箱(box)) to ensure that it was delivered safely.答案:1.had our car parked get our car battery charged 2. announced left 3. found ourselves very surprised 4. had her eyes fixed on 5. had a copy of the painting boxed二、用過去分詞對下列句子進行改寫。1. Loch Ness was surrounded by beautiful natural landscape, which made it look amazing.2. Carl and his friend stayed with a generous family who offered them bread with butter and honey that was homemade.3. The family’s ancestors once attended to soldiers who were wounded in the First World War.4. The young people were attracted by the legend of Loch Ness. They watched over the lake with their cameras and binoculars, which were positioned on the hill.答案:1. Loch Ness surrounded by beautiful natural landscape looks amazing.2. Carl and his friends stayed with a generous family who offered them homemade bread with butter and honey.3. The family’s ancestors once attended to wounded soldiers in the First World War.4. The young people attracted by the legend of Loch Ness watched over the lake with their cameras and binoculars positioned on the hill.

Step 5 While reading---Task 3Read the text again and answer the following questions.Q1: How many countries does the UK consist of ?4 Q2: What are the four countries of the United Kingdom?England, Wales, Scotland and Northern Ireland Q3: Which two were the first to be joined together ?England and WalesQ4: What are the two chief advantages of studying the history of a country ?The first one is to help you understand more about the country and its traditions.The second one is to make visiting it more enjoyable.Q5: What’s the author’s attitude towards studying the history ?Supportive/positiveStep 6 Post reading---Retell the textThe United Kingdom, Great Britain, Britain, England—many people are confused by (1)_____ these different names mean. In the 16th century, the nearby country of Wales (2) __________(join) to the Kingdom of England. In the 19 th century, the Kingdom of Ireland was added to create the United Kingdom of Great Britain and Ireland. Finally, the southern part of Ireland (3) ______ (break) away from the UK, which resulted in the full name we have today. However, most people just use the (4)_________(shorten) name: the UK. The four countries (5)__________ belong to the United Kingdom work together in some areas. There were four sets of invaders and the last group were the Normans. They had castles (6)_________(build) all around England and made changes (7)__________ the legal system. Studying the history of the country will make your visit much more (8)_________(enjoy). The capital city London is (9)___ ancient port city that has a history (10)______(date) back to Roman times. 1. what 2.was joined 3.broke 4.shortened 5.that 6. built 7.to 8.enjoyable 9.an 10.dating Step 6 Homework

Listening and Speaking introduces the topic of “Take part in a youth project”. The listening text is an interview about "sharing views on historical sites". Through listening to a dialogue between Chinese and foreign students on the way to the Confucius Temple, students can understand their views on the Confucius Temple, Confucius, Confucius' descendants and Confucius' educational thoughts, so as to realize and think about the profound influence of Confucius and his thoughts on Chinese historical tradition. At the same time, the dialogue naturally integrates English idioms and mentions Shakespeare, the British playwright, so as to provide language materials and context for students to understand English idioms and related cultural allusions, as well as to compare Chinese and foreign cultures, which is helpful for students to understand and express the language such as history, tradition, culture and custom significant impact.Text analysis: listening text is a dialogue between a British student and a Chinese student when he goes to the Confucius Temple. When William, a British student, visited the Confucius Temple, he asked Xiao Kong, a Chinese student, for directions. Xiao Kong was just going to the Confucius Temple to meet with the members of the research group, so they went together and exchanged their views on the Confucius Temple, Confucius, Confucius' descendants and Confucius' educational thoughts. From the perspective of foreign tourists, this paper describes their thoughts on Confucius, the great son of Confucius, who had a profound impact on Chinese history and cultural tradition, and his education.Listening and Talking introduces a visit to a historic tourist destination. Tourism is a common way to understand a country's history, culture, and customs and so on. Students listen to the dialogue between Xiao Yan, a youth hostel Usher, and Paul, a backpacker, to learn about Pingyao's famous historical and cultural attractions and Paul's travel experience and experience as a foreign tourist.

Features of languages1.Finally, in the 20th century, the southern part of Ireland broke away from the UK, which resulted in the full name we have today: the United Kingdom of Great Britain and Northern Ireland.該句是一個復(fù)合句。該句主句為:the southern part of Ireland broke away from the UK;which resulted in the full name we have today為which引導(dǎo)的定語從句代指前面整句話的內(nèi)容,we have today為定語從句修飾先行詞name。譯文:最后,在20世紀,愛爾蘭南部脫離英國,這導(dǎo)致了我們今天有的英國的全名:大不列顛及北愛爾蘭聯(lián)合王國。2.Almost everywhere you go in the UK, you will be surrounded by evidence of four different groups of people who took over at different times throughout history.該句是一個復(fù)合句。該句主句為:you will be surrounded by evidence of four different groups of people;其中Almost everywhere you go in the UK為讓步狀語從句; who took over at different times throughout history為定語從句修飾先行詞people。譯文:幾乎無論你走到英國的任何地方,你都會發(fā)現(xiàn)歷史上有四種不同的人在不同的時期統(tǒng)治過英國。3.The capital city London is a great place to start, as it is an ancient port city that has a history dating all the way back to Roman times.該句是一個復(fù)合句。該句主句為:The capital city London is a great place to start; as it is an ancient port city that has a history dating all the way back to Roman times.為原因狀語從句;dating all the way back to Roman times為現(xiàn)在分詞短語作定語修飾history。

這個地區(qū)有著深厚的傳統(tǒng)。既學(xué)既練:為了讓更多的外國游客了解中國文化,欣賞中國美麗的自然風(fēng)光,感受中國發(fā)生的巨大變化,某外文雜志社將出版一本英語小冊子來介紹中國的旅游景點。該雜志社邀請你為該小冊子寫一篇英語短文來介紹杭州,內(nèi)容包括:1.杭州的位置(中國東南部)、面積(16 000多平方公里)及歷史(2 200多年)等;2.杭州的旅游特色(自然風(fēng)景、傳統(tǒng)文化、特色小吃等);3.希望更多的游客來杭州參觀。注意:1.詞數(shù)80左右;2.可適當增加細節(jié),以使行文連貫。Located in the southeast of China, Hangzhou is a beautiful city.Dating back more than 2,200 years, Hangzhou covers an area of more than 16,000 square kilometers.In Hangzhou, you can visit the West Lake, whose scenery is fascinating.In addition, you can’t miss its cultural relics and historical sites, from which you will learn more about excellent Chinese traditional culture and traditions.In Hangzhou, the special snacks are famous and visitors from different parts of the world think highly of them.As a tourist attraction, Hangzhou attracts a large number of visitors from home and abroad every year.Once you come to China, Hangzhou is a scenic spot you can’t miss.

4. When he got absorbed in his world of music, he felt as if he could “see” the beauty of the world around him, like he had in his previous life.P·P as adverbial: _________________________________________________________________.Function: _______________________________________________________________________.Step 5 Solid Complete the passage with the words in brackets in their correct forms.Well known as a successful band, the Impact members show quite a few striking qualities. They never ever give up. When _____________(question) by the media, they are not _____________(discourage) and practise even harder. They are improving themselves by attending several master training class. They are united. _____________(fill with) team spirit, they act as a whole, always aiming for glory. Step 6 Difference and similarity from -ingObserve the following examples.1. He went out, shutting the door behind him.=He went out, ________________________________________________________.2. Not knowing what to do, he went to his parents for help.=__________________________________________, he went to his parents for help.Similarity: _______________________________________________________________________________________________________________________________________________________.Difference : _______________________________________________________________________________________________________________________________________________________.Step Practice1. ________ in a hurry, this article was not so good. 因為寫得匆忙, 這篇文章不是很好。2. ________ carefully, he found something he hadn’t known before. 他仔細讀書時, 發(fā)現(xiàn)了一些從前不知道的東西。3. ________ why he did it, the monitor said it was his duty. 當被問及他為什么要這么做時, 班長說這是他的職責(zé)

choir memberspeople to run food stands people to sell festival ticketspeople to sell music CDspeople to set up equipmentmusical performersStep 2: Listen to the announcement again and answer the questions. ? 1. What kind of songs will Grace Davis sing at the festival?? 2. Who can try out as a performer?? 3. What can those who think they do not have musical talent do?? 4. How can students volunteer to take part?? Talking about preferences:? Would you prefer doing ..?? What would you prefer to do?? Would you rather do .... or ….?? What would you rather do?? I'd prefer .... to ..? I'd rather have ... than .. Step 3: Speaking ProjectWork in groups. Role-play the conversation or make a new one.? Debbie: Where have you been? You missed the announcement about the music festival.? John: I was at the doctor's office. Music festival?? Frank: Yes, it's going to be next month on the school sports field. John, you can play the piano. How about playing it at the festival?? John: Well, I'd rather play the violin. I can play Liang Zhu.? Frank: Wow! Sounds good. What about you, Debbie? ? Debbie: Actually, I don't have much musical ability. I'd prefer just to help out with the crowds.? Frank: You can sell tickets or work at a food stand.? John: So can I assume that the aim of the festival is to raise money?? Debbie: Yes. All of the money will go to charity.

Step1:自主探究。1.(教材P52)Born(bear) in the USA on 2 January 1970, Whitacre began studying music at the University of Nevada in 1988.2.(教材P52) Moved(move) by this music, he said, “It was like seeing color for the first time.”3.(教材P56)I was very afraid and I felt so alone and discouraged(discourage).4.(教材P58)Encouraged(encourage) by this first performance and the positive reaction of the audience, I have continued to play the piano and enjoy it more every day.Step2:語法要點精析。用法1:過去分詞作表語1).過去分詞可放在連系動詞be, get, feel, remain, seem, look, become等之后作表語,表示主語所處的狀態(tài)Tom was astonished to see a snake moving across the floor.湯姆很驚訝地看到一條蛇正爬過地板。Finally the baby felt tired of playing with those toys.終于嬰兒厭倦了玩那些玩具。注意:1).過去分詞作表語時與被動語態(tài)的區(qū)別過去分詞作表語時,強調(diào)主語所處的狀態(tài);而動詞的被動語態(tài)表示主語是動作的承受者,強調(diào)動作。The library is now closed.(狀態(tài))圖書館現(xiàn)在關(guān)閉了。The cup was broken by my little sister yesterday.(動作)昨天我妹妹把杯子打碎了。2)感覺類及物動詞的現(xiàn)在分詞與過去分詞作表語的區(qū)別過去分詞作表語多表示人自身的感受或事物自身的狀態(tài),常譯作“感到……的”;現(xiàn)在分詞多表示事物具有的特性,常譯作“令人……的”。

This section focuses on "learning about experiencing music Online". This virtual choir is a new form of music performance. Members from all over the world don't need to love to come to a place. Instead, they use the new technology to model the various parts and wonderful virtual harmony group of music in the family. Students need to understand the main meaning of each paragraph. Finding topic sentences is an important way to understand the general idea of a paragraph. After the topic sentence, it is usually the detail sentence that supports and explains the topic sentence. Some paragraphs have obvious subject sentences, for example, the first sentence of the second paragraph is the subject sentence of the paragraph, and the following sentenceStudents need to pay attention to the topic sentences and key sentences, and then pay attention to how the sentences after the meaning explain, explain and support the topic sentences or key sentences before.1.Guide students to learn about experiencing music online2.Guide students to scan and circle the information in the text.3.Guide students to find the numbers and dates to fill in the timeline.4.Guide students to learn more about music by completing the sentences with the correct forms of the words and phrases. And then make a mind map about the outline of the passage.1. Guide students to pay attention to reading strategies, such as prediction, self-questioning and scanning.2. Help students sort out the main meaning of each paragraph and understand the narrative characteristics of "timeline” in illustrative style.3. Lead students to understand the changes that have been caused by the Internet.

The Internet celebrity Gao Yifeng. Years ago, he owned 5 companies and the staffs over 1,000, but during the economy crisis, he became nothing but debt. He was so worried that his hair became white overnight. There was a time when he wanted to killed himself. But after listening to the song Start Over by Liu Huan, he decided to cheer himself up. He started a steamed bun shop and gradually became a national chain shops. Now he became successful again.Walter Haddon said, “Music is the medicine of a troubled mind.” Music contains such a pleasant and inspiring force. Music gave him courage and bravery. When he listened to the song, it made his spirit fly like a kite in the wind. Music gave him strength and brought him relief. It was the rock I leant on to become strong and to get through those hard times. I hope none of us have to go through the same kind of suffering that he did. At the same time, we all go through various periods when we feel sad or alone. During those times, music can help us in the same way that it helped him. I hope we all will somehow begin to treasure music and make it a part of our life. Thank you for your listening !5.Revise your writing each other.Does he/she explain how music has changed his/her/someone else’s life?Are some of the rhetorical devices included and used properly ?Does he/she talk about how music makes him/her/someone feel?Is the first word in each sentences capitalised?Does he/she use correct punctuation ?

(4)Now we have heard a number of outstanding speeches ... 我們已經(jīng)聆聽了許多精彩的發(fā)言……(5)Because we wanted the nations of the world, working together, to deal with ... 因為我們希望全世界各國團結(jié)起來去應(yīng)對……(6)And if we do not act ... 如果我們不采取行動……(7)Now, I share the concerns that have been expressed ... 我也同意對于……表達的擔心(8)Let us show the world that by working together we can ... 讓我們告訴全世界,通過一起努力我們可以……(9)It is now time for us to ... 是時候我們……(10)And I have always wished that ... 我一直希望……(11)Thank you for letting me share this day with me.感謝你們和我共度這一天。實踐演練:假如你是高中生李華,你校將舉辦一次以“音樂”為主題的演講比賽,請你按照主題,寫下你的演講稿。注意:詞數(shù)100左右。First of all, thank you for listening to my speech. My topic is: love music like love yourself.Music is like the air we need to maintain our normal lives around us. You can't imagine how terrible a world without music would be. Movies and TV shows have no music, only dry conversations and scenes; mobile phones only vibrations; streets only noisy crowds; cafes, western restaurants only depressed meals. What a terrible world it is!As a student, I hope we all can enjoy the fun brought by music in our spare time. Instead of just listening to music, we can even make our own music. Let's enjoy the fun of music!Thanks again for your attention!

知識和技能 ⑴從圖片和簡易圖中,了解氣團(冷氣團、暖氣團)的概念;鋒的概念與分類;低壓(氣旋)、高壓(反氣旋)、高壓脊、低壓槽的概念。⑵從氣溫、氣壓、濕度、降水、風(fēng)等幾方面分析各種天氣系統(tǒng)的形成及其氣流特點,并綜合出各種天氣系統(tǒng)控制下的天氣狀況過程與方法 ⑴讓學(xué)生能閱讀和簡單分析天氣圖,解釋天氣變化現(xiàn)象;⑵用案例說明氣象災(zāi)害發(fā)生的原因和危害;⑶結(jié)合我國常見的天氣系統(tǒng)說明其對人們生產(chǎn)和生活的影響情感、態(tài)度與價值觀激發(fā)學(xué)生探究天氣的形成和變化的興趣和動機,培養(yǎng)學(xué)生求真、求實的科學(xué)態(tài)度,提高地理審美情趣教學(xué)重點1.鋒面系統(tǒng)。(鋒面系統(tǒng):一是要區(qū)別冷暖鋒的成因,二是要掌握鋒面兩側(cè)的氣壓、溫度、濕度、風(fēng)和天氣差異)2.低壓、高壓系統(tǒng)。(要掌握其成因、氣壓特征、氣流特征及其天氣特點四個方面。)

過渡:在實際生活中,城市內(nèi)部空間結(jié)構(gòu)并非完全按照這一經(jīng)濟規(guī)律呈現(xiàn),而是更具復(fù)雜性。這說明除了經(jīng)濟因素外,還有很多其他因素在起作用,請大家結(jié)合你的認識、圖2.9和案例1:紐約市的少數(shù)民族區(qū)談?wù)勀愕目捶ā#?)其他因素I收入——形成不同級別住宅區(qū)的常見原因。有能力支付昂貴租金和選擇最佳居住環(huán)境的人,其居住地往往形成高級住宅區(qū)。II知名度——城市內(nèi)某些地區(qū)在歷史、文化或經(jīng)濟方面具有很高的聲譽,這往往會吸引更多新的住宅或商場建在該處,以提高其知名度。III種族聚居區(qū)的形成——在有些城市的某一區(qū)域內(nèi),如果某個種族或宗教團體占優(yōu)勢,就可能形成種族聚居區(qū)。如紐約市的唐人街、哈林區(qū)、小意大利區(qū)等。IV歷史因素——城市的建筑物和街道設(shè)計可以維持久遠,早期的土地利用方式對日后的功能分區(qū)有著深遠的影響。

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(yīng)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)。
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