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  • 普利

    Rusty iron pulley with a rope wrapped around it suspended over a building.

    This rusty iron wheel has a rope wrapped around it. The wheel and rope hang over a building. Together they make up a type of called a pulley.
    ::这个生锈的铁轮环绕着绳子 轮子和绳子挂在一栋大楼上

    What Is a Pulley?
    ::什么叫普利? 什么叫普利? What is a Pulley?

    A pulley is a simple machine that consists of a rope and grooved wheel. The rope fits into the groove in the wheel, and pulling on the rope turns the wheel. Pulleys are generally used to lift objects, especially heavy objects. The object lifted by a pulley is called the load. The force applied to the pulley is called the effort.
    ::滑轮是一种简单的机器,由绳子和轮子组成。绳子与轮子的轮子接在一起,拉绳将轮子拉动。推轮通常用来抬举物体,特别是重物。滑轮抬起的物体称为负载。对滑轮施加的武力称为努力。

    Q : Can you guess what the pulley pictured above is used for?
    ::问题:你能猜到上面的滑轮是用来做什么的吗?

    A : The pulley is used to lift heavy buckets full of water out of the well.
    ::A:用滑轮把满满水的重桶从井里抬出来。

    Types of Pulleys
    ::推拉轮的类型

    Some pulleys are attached to a beam or other secure surface and remain fixed in place. They are called fixed pulleys. Other pulleys are attached to the object being moved and are moveable themselves. They are called moveable pulleys. Sometimes, fixed and moveable pulleys are used together. They make up a pulley. The three types of pulleys are compared in the Table . 
    ::一些滑轮附在横梁或其他安全表面,固定不变,称为固定滑轮,其他滑轮附在移动的物体上,可移动,称为移动滑轮,有时固定和移动的滑轮合在一起使用,构成滑轮,在表格中比较了三种滑轮。

    Q : Which type of pulley is the old pulley in the opening image?
    ::问题:开张图像中的旧拖车是哪类拖车?

    A : The old pulley is a single fixed pulley. It is securely attached to the beam above it.
    ::甲:旧拖车是固定的拖车,固定在上面的横梁上。

    Pulleys
    Type of Pulley How It Works Example No. of Rope Segments Pulling Up Ideal Mechanical Advantage Change in Direction of Force?
    Single fixed pulley

    A single fixed pulley used in a flagpole mechanism.

    Flagpole pulley
    ::旗杆滑轮

    A man raising a flag on a pole using a pulley system.

    		1 1 yes
    Single moveable pulley

    A single moveable pulley used in a zip-line setup.

    Zip-line pulley
    ::Zip-线滑轮

    A child using a zip-line pulley system, wearing a helmet and harness.

    		2 2 no
    Compound pulley (fixed & moveable pulleys)

    A compound pulley system with fixed and movable pulleys.

    Crane pulley
    ::Crane 滑轮

    A crane's pulley system against a blue sky, showcasing its lifting mechanism.

    		≥ 2 ≥ 2 varies

    Mechanical Advantage of Pulleys
    ::Pulleys的机械优势

    The of a simple machine such as a pulley is the factor by which the machine changes the force applied to it. The ideal mechanical advantage of a machine is its mechanical advantage in the absence of . All machines must overcome friction, so the ideal mechanical advantage is always somewhat greater than the actual mechanical advantage of the machine as it is used in the real world.
    ::滑轮等简单机器是机器改变其应用力的因素。机器最理想的机械优势在于没有机械优势。 所有机器都必须克服摩擦,因此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大一些。

    In a pulley, the ideal mechanical advantage is equal to the number of rope segments pulling up on the object. The more rope segments that are helping to do the lifting work, the less force that is needed for the job. Look at the table of types of pulleys. It gives the ideal mechanical advantage of each type.
    ::在滑轮上,理想的机械优势等于在物体上拉起的绳索段数。越多的绳索段有助于起吊工作,这项工作所需的力量就越少。看看滑轮类型的表格。它提供了每种类型的最佳机械优势。

    • In the single fixed pulley, only one rope segment pulls up on the load, so the ideal mechanical advantage is 1. In other words, this type of pulley doesn’t increase the force that is applied to it. However, it does change the direction of the force. This allows you to use your to pull on one end of the rope and more easily raise the load attached to the other end.
      ::在单一固定滑轮中,只有一根绳子拉起负载,因此理想的机械优势是1。 换句话说,这种滑轮不会增加它所使用的力力。 但是,它确实改变了力量的方向。 它允许你用绳子的一端拉起绳子,并更容易地提高与另一端连接的负荷。
    • In the single moveable pulley, two rope segments pull up on the load, so the ideal mechanical advantage is 2. This type of pulley doesn’t change the direction of the force applied to it, but it increases the force by a factor of 2.
      ::在单条可移动的滑轮中,两个绳子部分拉起装载,因此理想的机械优势是2。 这种滑轮不会改变对它施加的武力方向,但会增加2倍的力量。
    • In a compound pulley, two or more rope segments pull up on the load, so the ideal mechanical advantage is 2 or greater than 2. This type of pulley may or may not change the direction of the force applied to it—it depends on the number and arrangement of pulleys—but the increase in force may be great.
      ::在一个复合滑轮中,两个或两个以上的绳索段拉起装载,因此理想的机械优势是2或2以上。 这种滑轮可能改变,也可能不会改变对它使用武力的方向——这取决于滑轮的数量和安排——但力量的增加可能很大。

    Q : If a compound pulley has four rope segments pulling up on the load, by what factor does it multiply the force applied to the pulley?
    ::问题:如果一个复合滑轮有四个绳子段拉起装载,它会乘以什么因素使对滑轮施加的力成倍增加?

    A : With four rope segments, the ideal mechanical advantage is 4. This means that the compound pulley multiplies the force applied to it by a factor of 4. For example if 400 Newtons of force were applied to the pulley, the pulley would apply 1600 Newtons of force to the load.
    ::A:用四个绳索段,理想的机械优势是4。 这意味着,轮式轮船把对它施加的力力乘以4。 例如,如果对拉式轮船使用了400牛顿,则拖式轮船将1600牛顿用于装货。

    A block and tackle consists of two blocks, in which one block is fixed and the other is movable; the movable block is attached to the load. Play around with the simulation below to further explore the block and tackle:
    ::区块和钩子由两个区块组成,其中一个区块固定,另一个是可移动的;可移动区块附在负载上。

    Summary
    ::摘要

    • A pulley is a simple machine that consists of a rope wrapped around a grooved wheel. Pulleys are generally used to lift a load.
      ::滑轮是一种简单的机器,由一根绳子组成,缠绕着一个摇晃的轮子。 推轮通常用来抬起一个负荷。
    • There are three types of pulleys: fixed pulleys, moveable pulleys, and compound pulleys. Compound pulleys consist of two or more fixed and moveable pulleys.
      ::有三种型号的滑轮:固定滑轮、可移动滑轮和复合滑轮,复合滑轮由两个或两个以上固定和可移动的滑轮组成。
    • The ideal mechanical advantage of a pulley equals the number of rope segments pulling up on the load.
      ::滑轮最理想的机械优势 等于卸载的绳索段数

    Review
    ::回顾

    1. What is a pulley? What work do pulleys do?
      ::滑轮是什么 滑轮做什么工作
    2. Compare and contrast pulleys A and B in the illustration below.
      ::比较和对比滑轮A和B如下图所示。

    Comparison of two pulleys, A and B, illustrating different configurations and applied forces.

    1. In the compound pulley pictured below, how many Newtons of force are applied to the load if 200 Newtons of effort force are applied to the pulley?
      ::在下文所描绘的轮船复合体中,如果把200牛顿的力力用于拖车,对载荷施用多少牛顿的力?

    A compound pulley system with labeled forces and mechanical advantage.

    1. How would you construct a compound pulley with an ideal mechanical advantage of 6? 
      ::如何建造一个复合滑轮 其理想的机械优势是6?