小班講義高一物理第10講牛頓運動定律的應(yīng)用3——受力=

1、龍 文 教 育精品小班課程輔導(dǎo)講義講義編號 2013秋季 輔導(dǎo)科目： 物理 年級： 高一課 題第10講：牛頓運動定律的應(yīng)用3受力=運動教學(xué)目標教學(xué)重點、難點教學(xué)內(nèi)容一、已知受力情況確定運動情況1、牛頓第一定律： 牛頓第一定律定義了力：物體的運動不需要力來維持，力是改變運動狀態(tài)的原因。2、牛頓第二定律： 牛頓第二定律確定了運動和力的關(guān)系，使我們能夠把物體的運動情況與物體的受力情況聯(lián)系起來。3、牛頓第三定律： 牛頓第三定律說明了作用力與反作用力之間的關(guān)系，把相互作用的幾個物體聯(lián)系起來了。例題1：一個靜止在光滑水平地面上的物體，質(zhì)量是2 kg，在6.4 n的水平拉力作用下沿水平地面向右運動。求物體在

2、4 s末的速度和4 s內(nèi)的位移。（1）從題目中找出關(guān)于物理情景的描述。（2）研究對象是誰？它共受幾個力的作用，畫出受力圖。合力沿什么方向？大小是多少？（3）物體的運動是勻變速運動嗎？依據(jù)是什么？（4）完整寫出解答過程。拓展一：例題1中如果物體與地面間的“動摩擦因數(shù)是0.21 ”。求物體在4s末的速度和4s內(nèi)的位移，g=10m/s2。（1）物體受到的摩擦力應(yīng)該怎樣求？大小是多少？方向向哪？（2）畫出受力圖，寫出解答過程。拓展二：將例題1中的“水平拉力”改為“斜向上與水平方向成37角”，大小仍為6.4 n，其他條件均不變，求物體在4 s末的速度和4 s內(nèi)的位移。已知cos37=0.8，g=10m/

3、s2。（1）從題目中找出關(guān)于物理情景的描述。（2）研究對象是誰？它共受幾個力的作用，畫出受力圖。合力沿什么方向？（3）拉力與運動方向成一定夾角時，如何求合力？（4）完整寫出解答過程。拓展三：例題1中如果物體與地面間的“動摩擦因數(shù)是0.21 ”。將 “水平拉力”改為“斜向上與水平方向成37角”，大小仍為6.4 n，其他條件均不變，求物體在4 s末的速度和4 s內(nèi)的位移。已知cos37=0.8，g=10m/s2。（1）從題目中找出關(guān)于物理情景的描述。（2）研究對象是誰？它共受幾個力的作用，畫出受力圖。合力沿什么方向？（3）拉力與運動方向成一定夾角時，如何求合力？（4）完整寫出解答過程。例題2、一斜

4、面ab長為10 ,傾角為,一質(zhì)量為kg的小物體(大小不計)從斜面頂端a點由靜止開始下滑,如圖所示(取10 m/s2)(1) 若斜面與物體間光滑,求小物體下滑到斜面底端b點時的速度及所用時間.(2)若斜面與物體間的動摩擦因數(shù)為0.5,求小物體下滑到斜面底端b點時的速度及所用時間.二、已知運動情況確定受力情況1兩類動力學(xué)問題（1）已知物體的受力情況，求物體的運動情況。（2）已知物體的運動情況，求物體的受力情況。2應(yīng)用牛頓運動定律解決問題的一般思路（1）明確研究對象。（2）對研究對象進行受力情況分析，畫出受力圖。（3）以加速度的方向為正方向，與正方向相同的力為正，與正方向相反的力為負，列牛頓第二定律

5、的方程及其他相關(guān)方程。（4）解方程時，f、m、a都用國際單位制單位。3分析兩類問題的基本方法（1）抓住受力情況和運動情況之間聯(lián)系的橋梁加速度。力的合成分解受力情況f1、f2f合a受力情況v0、vt、s、t（2）分析流程圖f合=ma運動學(xué)公式 （強調(diào)：牛頓第二定律是“橋梁”，受力分析和運動分析是基礎(chǔ)，正交分解是方法。）例1、從靜止開始做勻加速直線運動的汽車，經(jīng)過t=10s，發(fā)生位移x=30m已知汽車的質(zhì)量m=4103kg，牽引力f=5.2103n求：（1）汽車運動的加速度大??；（2）運動過程中汽車所受的阻力大小做一做：1、一輛質(zhì)量為1000kg的小汽車正以10m/s的速度行駛，現(xiàn)在讓它在12.5

6、m的距離內(nèi)勻減速停下來，求所需阻力的大小。2、質(zhì)量為40kg的物體靜止在水平面上, 當在400n的水平拉力作用下由靜止開始經(jīng)過16m時, 速度為16 m/s, 求物體受到的阻力是多少?例題2、如圖所示，質(zhì)量為0.5kg的物體在與水平面成300角的拉力f作用下，沿水平桌面向右做直線運動，經(jīng)過0.5m的距離速度由0.6m/s變?yōu)?.4m/s，已知物體與桌面間的動摩擦因數(shù)0.1，求作用力f的大小。（g10m/s2）做一做：3 一個滑雪的人，質(zhì)量是75 kg，以v0=2 m/s的初速度沿山坡勻加速滑下，山坡的傾角=30，在t=5 s的時間內(nèi)滑下的路程x=60 m，求滑雪人受到的阻力（包括摩擦和空氣阻力

7、）。（1）從題目中找出關(guān)于物理情景的描述。（2）研究對象是誰？找出關(guān)于運動狀態(tài)的描述。（3）求出人的加速度，并畫出受力圖。合力沿什么方向？大小是多少？（4）怎樣求人受的阻力？完整寫出解答過程。 第 10 次課后作業(yè)學(xué)生姓名： 1一個質(zhì)量為21kg的物體同時受到兩個力的作用,這兩個力的大小分別為2n和6n,當兩個力的方向發(fā)生變化時,物體的加速度大小可能為( )a.1m/s2 b.2m/s2 c.3m/s2 d.4m/s22、一個物體從離地面一定的高度由靜止釋放，如果下落過程中受到的空氣阻力是物體重力的0.2倍，則物體下落的加速度大小是_m/s2。如果從地面上以一定的初速度豎直向上拋出一物體，受到

8、的空氣阻力仍是重力的0.2倍，則物體上升時的加速度大小是_m/s2。（g取10 m/s2）3、一個靜止在水平面上的物體，質(zhì)量為2 kg，受水平拉力f=6 n的作用從靜止開始運動，已知物體與平面間的動摩擦因數(shù)，求物體2 s末的速度及2 s內(nèi)的位移。（g取10 m/s2）4、質(zhì)量為20kg的物體若用20n的水平力牽引它，剛好能在水平面上勻速前進。求：（1）若改用50n拉力沿與水平方向成37的夾角向斜上方拉它，使物體由靜止出發(fā)在水平面上前進2.3m時，它的速度多大？（2）在前進2.3m時撤去拉力，又經(jīng)過3s，物體的速度多大？5、一個滑雪運動員沿與水平成30斜坡滑下，坡長400m，設(shè)下滑時運動員下滑時

9、沒有使用滑雪桿，他受到的平均阻力（包括摩擦力和空氣阻力）為下滑分力的1/5，求運動員從靜止開始到達坡底時的速度和時間。6、 質(zhì)量為1.5kg的物體在水平拉力f的作用下，從水平面上a點由靜止開始運動，運動一段距離后撤去該力，物體繼續(xù)滑行t2.0s停在b點，已知ab兩點的距離l5.0m，物體與水平面間的動摩擦因數(shù)為0.20，求水平拉力f的大小?7、一架救災(zāi)直升機從距離地面16 m的高處讓一箱物資由靜止開始落下，經(jīng)2 s物資落地，已知物資的質(zhì)量為10 kg，它下落過程中所受空氣阻力可認為大小不變。求空氣阻力的大小。（取g=10 m/s2）（1）找出關(guān)于物理情景的描述。屬于哪一類型的問題？解題的思路應(yīng)

10、該是什么？（2）研究對象是誰？受幾個力的作用，畫出受力圖。合力方向向哪？（3）寫出解答過程。待添加的隱藏文字內(nèi)容18、如圖所示物體以初速沿斜面上滑時加速度大小為6m/s2，沿斜面自由下滑時加速度大小為4 m/s2，試求物體與斜面間的動摩擦因數(shù)以及斜面的傾角。m9、（2009江蘇卷）航模興趣小組設(shè)計出一架遙控飛行器，其質(zhì)量m =2，動力系統(tǒng)提供的恒定升力f =28 n。試飛時，飛行器從地面由靜止開始豎直上升。設(shè)飛行器飛行時所受的阻力大小不變，g取10m/s2。 （1）第一次試飛，飛行器飛行t1 = 8 s 時到達高度h = 64 m。求飛行器所阻力f的大??； （2）第二次試飛，飛行器飛行t2 =

11、 6 s 時遙控器出現(xiàn)故障，飛行器立即失去升力。求飛行器能達到的最大寬度h；winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 1

12、00% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recent

13、ly named rugby league international federation player of the year sonny bill williams who has attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union aft

14、er triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary

15、 celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplin

16、ary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statem

17、ent the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds les

18、s than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drift

19、ing even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assum

20、e, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself

21、here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a team under-cooked - but i have been impressed by the kangaroos focus in their games since then.they have been concentrating on the sort of stuff that wi

22、ns you tough, even contests - strong defence, especially on their own goal-line, completing sets and a good kick-chase. theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.it is as though their entire tournament has been preparation for t

23、he final.in johnathan thurston, cooper cronk, cameron smith and either billy slater or greg inglis at full-back they have a spine that is unmatched in rugby league. they have played in so many high-pressure games - a priceless asset going into saturday.the kiwis are a lot less experienced but winnin

24、g a dramatic match like their semi-final against england will do wonders for their confidence.they defeated australia in the four nations final in 2010 and the last world cup, and know they can rise to the big occasion.winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over

25、 england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first

26、 pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recently named rugby league international federation player of the year sonny bill williams who has attracted the most intere

27、st in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this week

28、end, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow an

29、d i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of eur

30、opean footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission a

31、borted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move

32、through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratospher

33、e. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself