章节大纲

  • 常规

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  • 弹性力

    A bungee jumper mid-air, with the cord stretching as he falls near water and trees.

    What will happen to this bungee jumper when he reaches the end of the bungee cord? He won’t come to an abrupt stop. If he did, he might be seriously hurt. Instead, the cord will stretch while slowing his fall.
    ::当这只大腿跳跃器到达大腿绳的尽头时会怎样呢? 他不会突然停下来。 如果他停下来,他可能会受重伤。 相反,绳子会延缓,同时减慢掉下来的速度。

    Q : What will happen next?
    ::问:接下来会发生什么?

    A : The cord will only stretch so far, and then it will snap back to its original shape, causing the jumper to bounce back up. Bungee cords are useful for this purpose because they are elastic.
    ::A:绳子将只伸展到目前为止,然后它会折回原来的形状,导致跳跃器反弹。 邦基绳子对此有用,因为它们是弹性的。

    Elasticity and Elastic Force
    ::弹性力和弹性力

    Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity . As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force . The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape.  
    ::弹性物质在被拉伸或压缩后可以恢复到原来的形状。 此属性被称为弹性。 当您拉伸或压缩一个弹性物质时, 它会抵制形状的变化。 它会向相反的方向施加一种反力。 这支力量被称为弹性力量。 材料拉伸或压缩越远, 弹性力量就越大。 一旦拉伸或压缩力量释放, 弹性力量就会使材料回到原来的形状 。

    Q : What force stretches the bungee cord after the jumper jumps? When does the bungee cord snap back to its original shape?
    ::问题 : 跳跃后,什么力拉伸长了线? 线何时会恢复到原来的形状?

    A : After the bungee jumper jumps, he accelerates toward the ground due to gravity. His stretches the bungee cord. As the bungee cord stretches, it exerts elastic force upward against the jumper, which slows his descent and brings him to a momentary stop. Then the bungee cord springs back to its original shape, and the jumper bounces upward.
    ::甲:在大腿跳跃跳跃后,他因重力而加速向地面前进。他拉伸了大腿绳。当大腿绳伸展时,它向上伸展着弹性力,对着跳跃器,放慢他的下降速度,并把他带到一个短暂的停留点。然后,大腿绳向上跳动,跳跃器向上跳动。

    Launch the PLIX Interactive below to learn more about how elastic force affects a bungee jumper:
    ::启动下面的 PLIX 互动, 以了解弹性力如何影响大腿跳跃器:

    Using Elastic Force
    ::使用弹性力

    Elastic force can be very useful and not just for bungee jumping. In fact, you probably use elastic force every day. A few common uses of elastic force are shown in the Figure . Do you use elastic force in any of these ways?
    ::电磁力可以非常有用,而不仅仅用于大腿跳跃。事实上,你可能每天都使用弹性力。在图中显示了弹性力的一些常见用途。你是否在任何这些方面使用弹性力?

    Examples of elastic force: hair scrunchies, elastic waistband, rubber band, resistance band usage.

    Q : How does the band work? How does it use elastic force?
    ::问题:乐队是如何工作的?它是如何使用弹性力的?

    A : When you pull on the band, it stretches but doesn’t break. The resistance you feel when you pull on it is elastic force. The farther you stretch the band, the greater the resistance is. The resistance of the band to stretching is what gives your muscles a workout. After you stop pulling on the band, it returns to its original shape, ready for the next stretch.
    ::甲:当你拉起乐队时,它会伸展,但不会断裂。当你拉起它时,你感觉到的抵抗力是弹性力。你拉得越远,抵抗力就越大。乐队对伸展力的抵抗力就是使肌肉锻炼出来的力。在停止拉起乐队后,它会回到原来的形状,准备进入下一个展期。

    Springs like the spring toy pictured in the Figure also have elastic force when they are stretched or compressed. And like stretchy materials, they return to their original shape when the stretching or compressing force is released. Springs are used in scales to measure weight. They also cushion the ride in a car.
    ::像图中图画的弹簧玩具一样的弹簧在拉伸或压缩时也有弹性力。像伸展材料一样,当伸展力或压缩力释放时,它们又恢复到原来的形状。弹簧用在比例尺上测量重量。它们也把坐车的车坐坐垫放在垫子上。

    Colorful spring toy demonstrating elastic force by stretching and returning to its original shape.

    Q : Can you think of other uses of springs?
    ::问:你能想到泉水的其他用途吗?

    A : Bedsprings provide springy support beneath a mattress. The spring in a door closer pulls the door shut. The spring in a retractable ballpoint pen retracts the point of the pen. The spring in a pogo stick bounces the rider up off the ground.
    ::A: 床边的泉水在床垫下提供春支。 门边的泉水把门拉上。 收回的圆球点笔里的泉水把笔的点倒了起来。 松木棒里的泉水把骑手从地面上跳起来。

    Summary
    ::摘要

    • Elasticity is the ability of a material to return to its original shape after being stretched or compressed. When an elastic material is stretched or compressed, it exerts elastic force. This force increases the more the material is stretched or compressed.
      ::弹性度是指材料在被拉长或压缩后恢复原形的能力,当弹性材料被拉长或压缩时,它会施加弹性力,这种力会增加材料被拉长或压缩的程度。
    • Elastic force has many uses, from hair scrunchies to bed springs.
      ::电磁力有许多用途,从毛发和床头泉到床头泉。

    Review
    ::回顾

    1. What is elasticity?
      ::什么是弹性?
    2. How does an elastic material exert elastic force?
      ::弹性材料如何产生弹性力量?
    3. Explain how elastic force is used to shoot an arrow from a bow.
      ::解释一下如何使用弹性力从弓中射箭。