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    A hammer positioned on a wooden board, demonstrating how to pull out a nail.

    A hammer can be used to pull a nail out of a board. You can see how it’s done in this picture. When you push down on the handle of the hammer, the claw end of the hammer pulls up on the nail. A hammer is an example of a called a lever.  
    ::锤子可以用来把钉子从板子上拉出来。你可以看到这张照片是如何做的。 当你推倒锤子的把手时,锤子的爪子端会拉上钉子。 锤子就是称为杠杆的一个例子。

    What Is A Lever?
    ::什么是Lever? 什么是"Lever"? What is A Lever?

    A lever is a simple machine consisting of a bar that rotates around a fixed point. The fixed point of a lever is called the fulcrum. Like other machines, a lever makes work easier by changing the force applied to the machine or the over which the force is applied.
    ::杠杆是一种简单的机器,由在固定点周围旋转的棒组成。杠杆的固定点称为支架。与其他机器一样,杠杆通过改变对机器施压的力或施压的力使工作更容易进行。

    How does a hammer make it easier to pull a nail out of a board? First, it changes the direction of the force applied to the hammer—the hand pushes down on the handle while the claw end of the hammer head pulls up. Often, you can push down with more force than you can push up because you can put your own behind it. The hammer also increases the strength of the force that is applied to it. It easily pulls the nail out of the board, which you couldn’t do with your hands alone. On the other hand, the hammer decreases the distance over which the force is applied. The hand pushing down on the handle moves the handle over a distance of several inches, whereas the hammer pulls up on the nail only an inch or two.
    ::锤子如何使从板子上拉钉子更加容易? 首先,它改变了对锤子应用的武力方向 — 锤子头的爪子顶端拉上来时,手推倒了把手柄。 通常,你可以用更大的力推下来,因为自己可以自己推上去。 锤子也增加了对它施压的力量。 它很容易地将钉子拉出板子,而单靠手是无法做到的。 另一方面,锤子会缩短使用武力的距离。 把手推下手把柄拉到几英寸的距离,而锤子只拉到指甲上一两英寸。

    Q : Where is the fulcrum of the hammer when it is used to pull a nail out of a board? In other words, around what point does the hammer rotate?
    ::问题:锤子用来把钉子从板子上拉出来的时候,锤子的支架在哪里?换句话说,锤子在什么位置旋转?

    A : The fulcrum is the point where the head of the hammer rests on the surface of the board.
    ::A: 支架是锤头放在板板表面的点。

    Classes of Levers
    ::毕业班

    Other levers change force or distance in different ways than a hammer removing a nail. How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever. The output force is the force applied by the lever to the object. Based on the location of input and output forces, there are three basic types of levers, called first-class, second-class, and third-class levers. The Table describes the three classes. 
    ::其它杠杆会以不同方式改变力量或距离, 而不是用锤子去掉钉子。 杠杆会如何改变力量或距离取决于输入力和输出力相对于支架的位置。 输入力是用户对杠杆施加的力量。 输出力是杠杆对物体施加的力量。 根据输入力和输出力的位置, 有三种基本类型的杠杆, 称为一等、 二等和三等杠杆。 表格描述三个类别 。

    Classes of Levers
    Class of Lever Example of Lever in This Class Location of Input & Output Forces & Fulcrum* Ideal Mechanical Advantage Change in Direction of Force?
    First class

    Seesaw
    ::锯锯

    Two children on a seesaw, illustrating a first-class lever.

    Different classes of levers with labeled fulcrums and applied forces.

    1

    < 1

    > 1

    yes
    ::是 是

    yes
    ::是 是

    yes
    ::是 是

    Second class

    Wheelbarrow
    ::轮轴

    A green wheelbarrow with a single large wheel and two handles.

    A lever with two squares on one side and a fulcrum.

    		> 1 no
    Third class

    Hockey stick
    ::曲棍棒

    A hockey stick striking a puck, illustrating the concept of third class levers.

    Simple depiction of a first-class lever with two weights balanced on a beam.

    		< 1 no
    • Δ = fulcrum I = input force O = output force
      ::= fulcrum I = 输入力 O = 输出力

    The Table includes the ideal of each class of lever. The mechanical advantage is the factor by which a machine changes the input force. The ideal mechanical advantage is the increase or decrease in force that would occur if there were no to overcome in the use of the machine. Because all machines must overcome some friction, the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world.
    ::表格中包含了每一类杠杆的理想值。 机械优势是机器改变输入力的因素。 理想的机械优势是,如果机器的使用无法克服,就会出现力量的增减。 由于所有机器都必须克服一些摩擦,理想的机械优势总是比机器在现实世界中使用的实际机械优势要大一些。

    Q : Which class of lever is a hammer when it is used to pry a nail out of a board? What is its mechanical advantage?
    ::问:用哪类杠杆把钉子从板子上钉出来,是锤子?它的机械优势是什么?

    A : To pry a nail out of a board, the fulcrum is located between the input and output forces. Therefore, when a hammer is used in this way it is a first class lever. The fulcrum is closer to the output force than the input force, so the mechanical advantage is > 1. In other words, the hammer increases the force applied to it, making it easier to pry the nail out of the board.
    ::A: 将钉子从板子上刺出, 支架位于输入力和输出力之间。 因此, 当锤子这样使用时, 它是一个头等杆。 支架比输入力更接近输出力, 所以机械优势是 > 1. , 换句话说, 锤子会增加对它施加的力, 从而更容易将钉子从板上刺出。

    Launch  the simulation below to further explore how  a seesaw functions as a first class lever:
    ::启动以下模拟,进一步探索锯木如何作为头等杠杆发挥以下功能:

    Comparing Classes of Levers
    ::比较学前班的比较类

    All three classes of levers make work easier, but they do so in different ways.
    ::所有这三类杠杆都使工作更加容易,但它们以不同的方式这样做。

    • When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with first-class levers.
      ::当输入力和输出力在支架的对面时,杠杆会改变所应用武力的方向,这只有在头等杆上才会发生。
    • When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second-class and third-class levers.
      ::当输入力和输出力都在同一侧时,应用力的方向不会改变,这既包括二等和三等杠杆,也包括二等和三等杠杆。
    • When the input force is applied farther from the fulcrum than the output force is, the output force is greater than the input force, and the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers.
      ::当输入力比输出力更远的强度使用时,输出力大于输入力,理想的机械优势大于1时,这总是用二等杠杆发生,可能用一等杠杆发生。
    • When the input force is applied closer to the fulcrum than the output force is, the output force is less than the input force, and the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers.
      ::当输入力比输出力更接近电流时,输出力比输入力小,理想的机械优势小于1时,这总是与三等杠杆发生,可能与一等杠杆发生。
    • When the input and output forces are the same distance from the fulcrum, the output force equals the input force, and the ideal mechanical advantage is 1. This occurs only with first some first-class levers.
      ::当输入力和输出力与支架的距离相同时,输出力等于输入力,理想的机械优势是1。 只有在先使用一些头等杠杆时才会发生。

    Advantage of Third Class Levers
    ::三等中学生的优势

    You may be wondering why you would use a third-class lever when it doesn’t change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. The output end of the lever must move faster than the input end in order to cover the greater distance.
    ::您可能想知道, 当三等杠杆不改变应用力的方向或强度时, 您为什么会使用三等杠杆。 三等杠杆的优势在于输出力的运用距离大于输入力。 杠杆的输出端必须比输入端移动更快, 才能覆盖更大的距离 。

    Q : A broom is a third-class lever when it is used to sweep a floor (see the Figure ), so the output end of the lever moves faster than the input end. Why is this useful?
    ::问题:扫帚是用于扫地的三等杠杆(见图 ) , 因此拉杆的输出端移动速度比输入端更快。 为什么这有用 ?

    A : By moving more quickly over the floor, the broom does the work faster.
    ::A:通过在地板上更快移动,扫帚可以更快地工作。

    A person sweeping the floor with a broom, demonstrating a third-class lever in action.

    Launch the PLIX Interactive below to explore how your arm functions as a third class lever:
    ::启动下面的 PLIX 交互式活动, 探索您的手臂如何作为三等杠杆 :

    Summary
    ::摘要

    • A lever is a simple machine consisting of a bar that rotates around a fixed point called the fulcrum.
      ::杠杆是一种简单的机器, 由酒吧组成, 围绕一个固定点旋转, 叫做支架。
    • Based on the location of the input and output forces relative to the fulcrum, there are three basic types of levers: first-class, second-class, and third-class levers. The classes differ in their mechanical advantage and whether they change the direction of the input force.
      ::根据输入力和输出力相对于圆柱的位置,有三种基本杠杆类型:一等、二等和三等。 等级在机械优势和是否改变输入力方向方面有所不同。

    Review
    ::回顾

    1. What is a lever?
      ::什么是杠杆?
    2. In the broom pictured in the Figure , where is the fulcrum and where are the input and output forces applied?
      ::在图中图画的扫帚中,支架在哪里,投入和产出力量在何处应用?
    3. If you use a screwdriver to pry the lid off a paint can, which class of lever is the screwdriver? How does the screwdriver change the force that is applied to it? What is its ideal mechanical advantage?
      ::如果你用螺丝起子把涂料罐盖上盖子,哪类杠杆是螺丝起子?螺丝起子是如何改变对螺丝起子应用的力量的?它的理想机械优势是什么?
    4. Give an example of a lever that isn’t mentioned in the article. What is its class? 
      ::举一例说明文章中没有提到的杠杆。