动能、动能定理PPT教学课件.ppt

1、动能、动能定理PPT教学课件 我们已经知道，物体由于运动而具我们已经知道，物体由于运动而具有的能叫做动能，大家猜想一下动能与有的能叫做动能，大家猜想一下动能与什么因素有关？什么因素有关？实验：实验：动能与质量，速度的关系动能与质量，速度的关系返回返回结论：结论：物体的质量越大，速度越大，它的动能就物体的质量越大，速度越大，它的动能就越大。越大。那么，动能与物体的质量和速度之间有什那么，动能与物体的质量和速度之间有什么定量的关系呢？么定量的关系呢？实验：实验：公式推导公式推导 光滑水平面上有一质量为光滑水平面上有一质量为m的物体，初速度为的物体，初速度为 ，受到一，受到一与运动方向相同的恒力与运

2、动方向相同的恒力F作用，经过一段时间速度增加作用，经过一段时间速度增加到到 ,试求这个过程中合力的功。试求这个过程中合力的功。0VtVFa0VGFNFtV结论：结论：2202vvmmassFwt-=合合221mvEK=从上式我们看到，力F所做的功等于 这个物理量的变化。在物理学中就用 这个量表示物体的动能动能。动能用 来表示，即:221mv221mvkE2022121mvmvwt-=合一一.动能动能 概念：物体由于运动而具有的能叫做动能。概念：物体由于运动而具有的能叫做动能。物体的动能等于物体的质量与物体速物体的动能等于物体的质量与物体速 度的二次方的乘积的一半。度的二次方的乘积的一半。定义式

3、定义式:,V是瞬时速度。是瞬时速度。单位：焦（单位：焦（J）221mvEK=动能概念的理解：动能概念的理解：动能是动能是标量标量，且只有正值。，且只有正值。动能具有动能具有瞬时性瞬时性，在某一时刻，物体具，在某一时刻，物体具 有一定的速度，也就具有一定的动能。有一定的速度，也就具有一定的动能。动能具有动能具有相对性相对性，对不同的参考系，物体，对不同的参考系，物体 速度有不同的瞬时值，也就具有不同的动速度有不同的瞬时值，也就具有不同的动 能，一般都以地面为参考系研究物体的运能，一般都以地面为参考系研究物体的运 动。动。二二.动能定理动能定理W=21KKEE-EK=2022121mvmvwt-=

4、合221mv外力的总功外力的总功末状态动能末状态动能初状态动能初状态动能力在一个过程中对物体所做的功，等于物体在这个过力在一个过程中对物体所做的功，等于物体在这个过程中的动能的变化，这个结论叫做程中的动能的变化，这个结论叫做动能定理动能定理。思考与讨论：思考与讨论：如果物体受到几个力作用如果物体受到几个力作用,动能定理动能定理中的中的W表示的物理意义是什么？表示的物理意义是什么？合外力所做的总功合外力所做的总功动能定理更一般的表述方式是：动能定理更一般的表述方式是：合外力在一个过程中对物体做的合外力在一个过程中对物体做的总功总功，等于物体在这个过程中动能的变化。等于物体在这个过程中动能的变化。

5、2022121mvmvwt-=合即：即：W=21KKEE-1、合外力做、合外力做正功正功，动能，动能增加增加 合外力做合外力做负功负功，动能，动能减少减少2、动能定理中的功是合外力做的总功、动能定理中的功是合外力做的总功 总功总功的求法：的求法：（1）先求合力，再求合力功）先求合力，再求合力功 （2）先求每个力做的功，再求代数和）先求每个力做的功，再求代数和3、适用范围：、适用范围：既适用于既适用于恒力恒力做功，也适用于做功，也适用于变力变力做功；做功；既适用于既适用于直线直线运动，也适用于运动，也适用于曲线曲线运动运动。动能概念的理解：动能概念的理解：需要注意的几点需要注意的几点:(1)(1

6、)动能定理一般用于处理力和运动的综合问题动能定理一般用于处理力和运动的综合问题(2)(2)合外力做功的求解方法合外力做功的求解方法:一种是先求出合外力，然后求总功，表达式为一种是先求出合外力，然后求总功，表达式为解题思路解题思路:(1)1)选取研究对象选取研究对象.一般选取某一个物体或相对静止的多一般选取某一个物体或相对静止的多 个物体做研究对象个物体做研究对象.(2)(2)确定研究过程确定研究过程.研究过程可以是物体运动中的某一阶研究过程可以是物体运动中的某一阶段段,也可以是由物体运动的多个阶段所组成的全过程也可以是由物体运动的多个阶段所组成的全过程.(3)(3)在确定的研究过程内在确定的研

7、究过程内,对研究对象进行力的分析和功对研究对象进行力的分析和功的分析的分析.在进行功的分析时在进行功的分析时,不但要分析哪些力做功不但要分析哪些力做功,还还要分析其做功性质要分析其做功性质.(4)(4)确定研究对象的初、末动能及动能的变化确定研究对象的初、末动能及动能的变化.这里的初这里的初和末是相对所选取的研究过程来讲的和末是相对所选取的研究过程来讲的.(5)(5)应用动能定理列出相应关系式应用动能定理列出相应关系式.返回返回1、1970年我国发射的第一颗人造地球卫 星，质量为173kg，运动速度7.2km/s，它的动能是多大？2、对于做匀速圆周运动的物体，下面说法中正确的是（B ）A 速度

8、在改变，动能也在改变 B 速度在改变，动能不变 C 速度不变，动能不变 D 动能、速度都不变3 3、将一石子在将一石子在h高处斜抛出去，抛速为高处斜抛出去，抛速为v0，求：，求：（1）人对石子做功）人对石子做功W1=？（2）石子落地时速度）石子落地时速度vt=？（1）由于不知抛力，且为变力，其抛石过程的位移不知。由功的公式无法求，但石子初末状态的动能已知。由则 ，方便求得W1.（2）石子初动能为零，末动能为.由动能定理 4 4、质量为的小球，从半径的半圆形槽的边缘A点沿内表面开始下滑，到达最低点B的速度。求在弧AB段阻力对物体所做的功。解析：物体在弧AB段运动过程中受重力、弹力和阻力作用，其中

9、弹力和阻力是变力，但在此过程中弹力对小球不做功；重力是恒力，在这一过程中，重力的功mgRWG=由动能定理有：WWmvGf=-1202mgRmvWmvWGf-=-=222121 解得：结论：结论：返回返回动能定理既适用于直线运动，也适用于曲线运动，既适用于恒力做功，也适用于变力做功。力做功时可以是连续的，也可以是不连续的，可以是在一条直线上的，也可以是不在一条直线上的。一、动能一、动能 1、定义：物体由于运动而具有的能量叫做动能、定义：物体由于运动而具有的能量叫做动能 2、表达式：、表达式：3、单位：焦耳（、单位：焦耳（J）二、动能定理、动能定理 1、内容：合力所做的功等于物体动能的变化、内容：

10、合力所做的功等于物体动能的变化 2、表达式：、表达式：返回返回221mvEK=2022121mvmvwt-=合pyramid 金字塔Stonehenge 巨石阵wheel 车轮golden sunlight.金色阳光Tiananmen Square 天安门广场 军队Jay Chou 周杰伦Jay Chou is handsome.He is my favourite actor.arrow 箭bow 弓 The Trojan War the Trojan War told in HomersIliad and Odyssey 荷马伊利亚特奥德赛 the prince of Troy fell

11、in love with Helen,the queen of Sparta.斯巴达 He kidnapped her and took her to Troy.All the Greek went to bring her back.绑架 the war lasted for ten years.The night of the horseLook at the title,the picture and the last paragraph,and then answer the two questions.It was a huge wooden horse.1.What kind of

12、 horse it is?2.How did the Greeks win the war?They won the war with a trick.Read through the whole passage and match the main idea for each part.P1-2P3-6P7P8-9The Trojans celebrate their victory and then go to sleep.The Greek soldiers inside the horse open the city gates and let in the Greek army.Th

13、e Greek army capture Troy.A Trojan soldier announces that the Greek army has left and his captainConfirms it.The soldier found a huge,wooden horse outside their city,and the captainorders it to be moved into the city.1.How was the soldier probably feeling when he came down the stairs,surprised or pe

14、aceful?2.What did the captain think when he saw the empty plain?3.What did the captain think about the horse?4.What did the citizens of Troy do that night?5.Where did the six Greek soldiers hide?6.Did the horse have something to do with the trick?How?Read the passage and then answer the following qu

15、estions1.How was the soldier probably feeling when he came down the stairs,surprised or peaceful?2.What did the captain think when he saw the empty plain?3.What did the captain think about the horse?Read the passage and then answer the following questionsHe probably was feeling surprised.The captain

16、 thought that they had won the war.He thought it was too big for the Greeks to take.4.What did the citizens of Troy do that night?5.Where did the six Greek soldiers hide?6.Did the horse have something to do with the trick?How?They celebrated their success.They hid in the horse.Yes.(answers vary.)Par

17、t B Look and think These pictures show some of the events in the story on Page 58.Arrange them in the correct order.Answers:c d b a f e Summary The war between the Troy and the Greeks lasted ten years.At last,the Greeks won the war with a t_.They pretended to leave the city of Troy,but they left a h

18、uge w_ horse behind.The Troy thought they have w_ the war so they c_,making j_ about the Greeks.They were so happy about their win that all of them went to sleep,i_ the gate guard.The Greek soldiers i_ the wooden horse opened the gate and let their army in.In this way,they c_ the Troy city.rickooden

19、onelebratedokesncludingnsideaptured1.大木马2.举行一次比赛3.冲下台阶4.一会儿后5.朝下看6.再多等一小时7.进入城里8.拿走，带走9.除之外10.拖进城11.开玩笑12.成功做成某事13.用计谋a huge wooden horsehave hold run a competitionrush down the stairsseconds laterlook down atwait for another hour=wait for one more hourenter the city=get into city take awayexcept fo

20、rpull/drag into the citymake jokes about=laugh at=make fun ofsucceed in doing sth.with a trick Useful expressions1.A newspaper ran a short competition on famous tales from pete(v)比赛比赛-competition competitor competitive(n.)比赛(n.)比赛者(adj.)比赛的2.Seconds later,the captain stood on the high wall of the ci

21、ty of Troy,and looked down at the empty plain.(1)seconds later=after a while 一会儿后一会儿后(几秒钟后几秒钟后)(2)the city of Troy 特洛伊城特洛伊城 the city of Shenzhen=Shenzhen city (3)look out=be careful look for 寻找寻找 look after 照顾照顾 look over=examine look down upon sb 看不起某人看不起某人 look up to 看得起，尊重看得起，尊重 3.It was too big

22、for them to take with them.=It was so big that they couldnt take it with them.take bring carry随身携带4.They all went to sleep,including the gate guards.The band played many songs,including some of my favorite.十个人出席了会议，包括我爸爸。十个人出席了会议，包括我爸爸。Ten members are present at the meeting,including my father.5.By

23、midnight,the square was empty,except for the giant horse.except for:not including 除除 之外（不包括）之外（不包括）Except for one old lady,the bus was empty.比较：比较：We go to school every day except Saturday and Sunday.We have winter holiday besides summer holiday.6.The six Greek soldiers in the wooden horse waited fo

24、r another hour,to be sure.We need another ten students =We need ten more students.Paraphrase 1.The Greeks tried to capture our city.2.The square was empty,except for the giant horse.3.They succeeded in capturing it with a trick.The Greeks tried to take over our city.There was nobody but the giant ho

25、rse in the square.There was only a giant horse in the square.They managed to capture it with a trick.They captured it successfully with a trick.1 d-2 h-3 a-4 e-5 b-6 g-7 c-8 fTroySpartaGods and GoddessesKing of TroyKing MenelausKing of the GodsZeusPrince ParisQueenHelenGoddess of loveAphroditeHow di

26、d the Trojan War start?1 d-2 h-3 a-4 e-5 b-6 g-7 c-8 fTranslate the following sentences1.我已经写了几个电脑游戏。2.我经营这家公司两年了。3.你把你的书整理好了吗？4.我还没有把衣服挂起来。5.他铺床铺了吗？I have already written several computer games.I have run the business for two years.Have you organized your books?I havent hung up the clothes.Has he m

27、ade the bed?现在完成时结构：现在完成时结构：have/has+动词过去分词动词过去分词1.规则动词规则动词finish-finished-finishedlive-lived-livedcarry-carried-carriedstopstopped-stoppedfailorganizeachieveempty-failedfailed -organized-organized -achieved achieved -emptied emptied2.不规则动词gowentgonesee-sawseenforgetspendsweephang forgot forgotten s

28、pent spent-swept-swept-hung-hung (1).for+表示一段时间的短语 (2).since+表示过去时间点的词语 (3).since+表示过去时间的时间状语从句eg.I have been a teacher _ a year.He has been at this school _ 1992.We have learned 1,000 English words _ we came to this school.forsincesince already,yet;never,ever;just,before 有此类副词时,常强调动作完成.eg.Have you

29、_been to Japan?I have _ finished my homework.I have _ finished my homework.I havent finished my homework _.everjustalreadyyet二.现在完成时句中常见的时间词1.Weve already finished the work.I havent swept the floor yet.Have you emptied the rubbish bin yet?already 已经用于肯定句 yet 还用于疑问句和否定句2.She has never heard of it,has

30、 she?Have you ever been to England?never从未没做过 ever曾经做过3.Ive just written several computer games.I have watched this film before.just 刚刚 before 以前 用 since,for或者ago填空1.Jill has been in Ireland _ Monday.since2.Jill has been in Ireland _ three days.for3.My aunt has lived in Australia _ 15 years.for4.Mar

31、garet is in her office.She has been there _ 7 oclock.since5.Mike has been in hospital _ October.since6.They got married six months _.ago7.I first met Sue two years _.ago三.区分短暂性动词与持续性动词.表示短暂性(瞬间性)的动词在现在完成时的句中不能和一段时间连用.即for,since短语或how long问句1.I came here two years ago.I have been here for two years.I

32、 have been here since two years ago.2.I joined the army 5years ago.I have been a soldier for 5 e/arrivego out leavebeginbuyborrowjoindiecatch a coldbe at/in be outbe away(from)be onhavekeepbe a member ofbe deadhave a cold瞬间动词和延续性动词转换练习：1.I bought the book two days ago.I have had the book for two day

33、s.2.He borrowed the book three months ago.He has kept the book since 3 months ago.3.I got to know Jane 2 years ago.I have known Jane for 2 years.4.I joined the League three years ago.I have been a League member for 3 years.5.Ken joined the army two years ago.Ken has _ _ _ for two years.Ken has _ _ t

34、he army for two years.been a soldierbeen in6.He left his hometown 10 years ago.He has _ _ _ his hometown since 10 years ago/for 10years.been away from7.The film began 10 minutes ago.The film has _ _ for 10 minutes.been on8.I got a cold two days ago.I have _ a cold since two days ago.had9.The film fi

35、nished 5 minutes ago.The film has _ _ for 5 minutes.been over10.The man came here ten minutes ago.The man has _ here for 10 minutes.been11.Linda and Frank married in 1989.They _ since 1989.have been married改错:How long have you become a league member？For more than one year.Have you arrived here since

36、 last night.Yes，youre right.The dog has died for a month.He has gone to Shanghai twice.How long have you been at this school?Since two years.beenbeenbeen deadbeen ago.For IV.exercise1.My mother_ the windows already,so the room looks much brighter.A.has cleaned B.had cleaned C.is cleaning2.The engine

37、er _ shopping with his wife yesterdayA.has gone B.has went C.went3.-Wheres your mother?-She _ the hospital.A.has gone to B.has been to C.has gone in 4.Oh,Mrs.King,your necklace looks nice.Is it new?No,I _ it for two years.A.had B.have had C.bought D.have bought 5.I havent seen you _ last Friday.A.fo

38、rB.since C.fromD.on6.His grandfather _ for over two years.A.has died B.has been dead C.has dead D.died Tell your friends about the Troy war in your words.(more than 80 words)Read the passage again and then correct the wrong statements1.The captain was sad to see the empty plain.2.The horse was on wheels.3.The Trojans pushed the horse into the city.4.The gate guard went to sleep,too.5.The gate guard opened the main gates.6.The Troy lost the war.happydraggedGreek soldiers