邢秀娜豎直方向圓周運(yùn)動(dòng)中的向心力

1、Centripetal Force向心力Circles at amusement parks游樂(lè)場(chǎng)中的豎直圓周運(yùn)動(dòng).理綜組理綜組邢秀娜邢秀娜Uniform Circular MotionUniform circular motion （勻速圓周運(yùn)動(dòng)）occurs when the speed （速率)of an object experiencing circular motion remains constant.Is velocity（速度） constant for uniform circular motion?No. The velocity is always changing d

2、irection.知識(shí)回顧（勻速圓周運(yùn)動(dòng)）知識(shí)回顧（勻速圓周運(yùn)動(dòng)）why 演示演示 線線的一端系一小球，使小球的一端系一小球，使小球在光滑水平面在光滑水平面上作上作勻速圓勻速圓周運(yùn)動(dòng)周運(yùn)動(dòng)uniform circular motion。一、什么叫向心力Centripetal Force ？ 觀察并思考：觀察并思考： 1、小球的受力情況如何、小球的受力情況如何？(draw free body diagram) 2、線的拉力、線的拉力方向方向(direction)有有何特點(diǎn)？何特點(diǎn)？ 想一想：向心力的方向向心力的方向direction 是否改變是否改變？ 迫使物體做勻速圓周運(yùn)動(dòng)，方向總是沿半徑指迫

3、使物體做勻速圓周運(yùn)動(dòng)，方向總是沿半徑指向圓心的力叫向心力向圓心的力叫向心力。注意：向心力是從力的作用效果命名的注意：向心力是從力的作用效果命名的OFFFVVVO 分析：分析： 結(jié)論：結(jié)論：向心力的方向向心力的方向(direction) (direction) 是在不斷變化是在不斷變化(change)(change)的的 Non-Uniform Motion非勻速圓周運(yùn)動(dòng)（重點(diǎn)）Accelerating （加速）into the loop the first time.At the top of the loop, the car will experience Fc = Fg + FN.Whi

4、ch forces are centripetal forces?Normal force （正交反作用力） and weight引力.誰(shuí)來(lái)提供向心力？What if the car goes around a second time?And we only use the force of gravity（引力） as the accelerating force?Suppose the car moves more slowly, so that Fc = Fg. The track doesnt exert FN on the car to keep it moving on the t

5、rack. What if the car moves too slowly?The Fc FgThe car will fall down.Minimum speed（最小速度） around a loopThe slowest any car can go around the track is a speed that requires a centripetal force that has a magnitude equal to gravity. Fc=FgWhat about tension（張力）?Top of CircleWhich forces are centripeta

6、l?Fg and FT. So: Fc = Fg + FTSides of the circleWhich forces are centripetal?Only FT is Fc.So, Fc = FTWhich forces are centripetal?FT and FgNow, Fg isnt directed towards the centre, but its parallel in the opposite direction.Fc = FT -FgCentripetal Force (F = ma)Newtons Second Law of Motion 牛頓第二定律牛頓第二定律 Fc = mv2/rFc = mr2Practice 1A bucket of water with a mass of 1.5 kg is spun in a vertical circle on a rope. The radius of the circ