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九年级物理滑轮3


1 如图所示的滑轮组中的 甲轮是什么滑轮,乙轮是什么 滑轮?若不计滑轮的重及摩擦, 则(1)已知物体重12N,绳端 所用拉力多大?(2)若实际测 得绳端的拉力F/为5N,则所吊 起的物体重G/多大?(3)物体 被吊高0.3m,则绳端向上拉动 多少m?

F 甲



2画一个滑轮组,使拉力是物 体重G的1/3,人的拉力方向向下, 要求所用的滑轮最少。(不计滑 轮重力和摩擦力) 答案如右图所示

F G

例3

F1 F2

F3
图1 图2 图3 分别用如图所示的滑轮组匀速提起同一重物时所用的拉 力分别为F1、F2、F3,若不计滑轮重和摩擦,这三个拉 力按从小到大排列的顺序为------------------F2、F1、F3

定 滑轮,B是 1 如图所示:A、B两个滑轮中,A是 --------动 ---------滑轮,在不考虑滑轮摩擦和重力情况下物体与桌 30 牛。 面的摩擦力为90牛,匀速移动物体,水平力F为---------F B A

2 如图所示:一根绳子绕过定滑轮, 一端挂在重物G上,手拉另一端,分 别用F1、F2、F3拉重物,则( D ) A F1较大 B F2较大 C F3较大 D 三个力一样大

F3

F1

F2

1 如图所示:物体A、B都处于静 止状态,它们所受的重力分别是6N 和14N,关于它们的受力情况,下面 说法中正确的是( BC ) A 物体A受到合力是14N B 物体B受到重力与拉力的合力为8N C 物体A受到合力是零 D 物体B受到的拉力与地面的支持 力是8N

A

B

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CHAPTER I A STROLLING PIANO“Why did she choose ‘Morning -Glory’ as her tribe name?” asked M?nkw?n the Rainbow of Sesooā the Flame , as Rainbow and Flame, with girlish arms entwining, stood beneath the shelter of the Silver Twins, two kingly birch-trees, so identical in stature even to their topmost jeweled crowns of leaves flashing in the July sun, so alike in the silver symmetry of each fair limb as to be named the Twins .These silver kings were one-hearted, too, in their benevolent purpose in life, which was to unite in casting a brotherly shade over a certain corner of the broad city playground, dotted with children from every clime, and incidentally to fan the flushed cheeks of the two girls directly benea th them, bound together by a girdling rainbow that played about their waists, woven by the sun’s shuttle amid the quivering birch -leaves, fit symbol of their binding Camp Fire sisterhood.Sesooā’s eyes danced, lit by a tiny golden flame that uncurled itself in their demure hazel like a firefly alighti ng on a brown leaf. She caught her lower lip between the pretty incisors that decorated the front of her mouth as she scrutinized the semi -distant figure of a sixteen-year-old girl—perhaps nearer to seventeen—clad in a loose lavender smock to her knees, whence to her ankles there was a gleam of white skirt, with the most bewitching, frilled summer “Tam” of lavender, matching her smock, shielding her brown head, sheltering her face, like the hoo d of a flower. This floral figure leaned against the open door of a handsome automobile which was standing upon the playground avenue.“I’m sure i t’s beyond me to tell why Jessica Holley (Jessica Dee Holley; she always likes to bring the unusual little middle name in, because it was her mothe r’s, I suppose), why she chose Welatáwesit, which is the only Indian equivalent she could find for Morning -Glory—literally meaning ‘Climbing Plant’ or ‘Pretty Flower’ for her Camp Fire name. But I believe there’s a story attached to the choice, some ‘cunning’ little anecdote of her childhood. Wi sh I could ferret it out! She seems, always, to have been called ‘Glory,’ nearly as much as Jessica,” answered Sesooā racily, she who in every -day life bore no flaming cognomen, but was plain little, gay little, Sally Davenport, as full of quips and quirks, of lightning impulses and sudden tu rns as the wheeling firefly in her eyes.“Goody! I’d like to hear the anecdote, too. The Morning -Glory name suits her so well that I thought she must have dreamed it—that it came to her in sleep—as I dreamed mine,” laughed the Rainbow, whose rightful name when she was not clad in a leather -fringed robe of khaki, in moccasins and head-band, and seated by a Council Fire, was Arline Champion. “But I call it absurd, meanly absurd, that if there’s any stor y about her and her name, we should not hear it, we who have named our Camp Fire (and it’s the best in the city, too, though I say it myself!), o ur whole group or tribe of fourteen girls, after her,” she went on with a stamp of her foot on the playground sod and with rainbowed emphasis; she was t he shell-tinted, demurely shining kind of fifteen-year-old girl who unconsciously aims at carrying a rainbow in her pocket, to brighten the dull or tear-wet day.“Oh! we didn’t exactly ‘name it after her,’” demurred Sally. “She happened to come here last winter to visit those rich girls, the Deerings, who are all fluff an’ stuff; that exactly describes them, Olive and Sybil ——” There was the least little green tinge of the spitfire about Sesooā’s fla me now as she shot a glance toward two girls seated in the waiting automobile together with an older woman, evidently chaperon to the band of girl s. “Oh! I say, pinch me; I shouldn’t have said that, should I, seeing that they brought us here in their car? But ’twas the first time they ever did it, though my father is head-bookkeeper in their father’s office at the Works; and I’ll engage ’twas Morning -Glory—Jessica—who suggested it, as we all wanted to visit this playground where there are so many foreign children, to see them dance their folk dances,” she ran on, speech flitting away f rom its starting-point in the wake of her firefly dance, which vivaciously hovered from one object or group of objects to another.Arline waited for it to alight again on Jessica, as it presently did.“Well! as I was saying,” reverted Sally, “you remember how she came here last February just when we were beginning to organize our Camp Fire group, when we had secured Miss Darina Dewey as Guardian (I think she’s a love of a Guardian and I like her unu sual first name, too, though some of the girls don’t!) but before we had applied for our Charter, when we were searching for a name for our new Cam p Fire circle, raking over Indian names like leaves until —goodness! we seemed half-smothered in them.” Sally paused for breath, breathlessly smothered, ind eed, by the sunlit torrent of her own words, which had a trick of inundating a listener.“It was at our second meeting, I think, at Miss Dewey’s house,” she went on, “that Jessica came in, all snow an’ sparkle from her eyes to her toes, and introduced herself by showing a transfer card sign



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