章节大纲

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  • 复合机

    Close-up of a bicycle wheel showing gears, chain, and spokes as simple machines.

    Did you ever look closely at the moving parts of a bicycle? You can see some of them in the opening image. Do you see any simple machines, such as pulleys, wheels and axles, levers, or screws? A bicycle consists of many simple machines. It's an example of a compound machine.
    ::您是否仔细看过自行车移动部分? 您可以在打开的图像中看到其中的一些部分。 您是否看到任何简单的机器, 如滑轮、轮轮和轴、杠杆或螺丝? 自行车由许多简单的机器组成。 这是复合机器的一个例子 。

    What Is a Compound Machine?
    ::什么是复古机器?

    A compound machine is a that consists of more than one simple machine. Some machines consist of just two simple machines. You can read below about two examples—the wheelbarrow and corkscrew. Other compound machines, such as bicycles, consist of many simple machines. Big compound machines such as cars may consist of hundreds or even thousands of simple machines.
    ::复合机器由不止一台简单的机器组成,有些机器只由两台简单的机器组成。下面可以读到两个例子:手推车和软木车。其他复合机器,如自行车,由许多简单的机器组成。汽车等大型复合机器可能由数百甚至数千台简单的机器组成。

    Wheelbarrow
    ::轮轴

    Look at the wheelbarrow in the Figure . It is used to carry heavy objects. It consists of two simple machines: a and a . Effort is applied to the lever by picking up the handles of the wheelbarrow. The lever, in turn, applies upward force to the load. The force is increased by the lever, making the load easier to lift. Effort is applied to the wheel of the wheelbarrow by pushing it over the ground. The rolling wheel turns the axle and increases the force, making it easier to push the load.
    ::查看图中的手推车。它是用来运载重物的。它由两台简单的机器组成:一和一。通过捡起手推车的把手把努力应用到杠杆上。 杠杆反过来又向上施压到负荷上。 武力由杠杆增加, 使负荷更容易提升。 将手推车推倒地面, 将脚推到手推车的轮子上。 滚轮将轴转动, 增加力量, 使推车更容易。

    Diagram highlighting wheelbarrow components: lever and wheel and axle for lifting and transport.

    Corkscrew
    ::装瓶机

    The corkscrew in the Figure is also a compound machine. It is used to pierce a cork and pull it out of the neck of a bottle. It consists of a and two levers. Turning the handle on top twists the screw down into the center of the cork. Then, pushing down on the two levers causes the screw to pull upward, bringing the cork with it. The levers increase the force and change its direction.
    ::图中的螺旋桨是复合机器。 它用来穿透一个螺旋桨, 把它从瓶子的脖子上拉出来。 它由一个和两个杠杆组成。 将顶部的把手把螺丝扭到瓶子的中心。 然后, 推倒两个杠杆, 使螺旋向上拉动, 并随着它拉动瓶子。 杠杆会增加力量, 并改变方向 。

    A corkscrew labeled with parts: screw and two levers used to extract corks.

    Efficiency of Compound Machines
    ::复合机器的效率

    is a force that opposes motion between any surfaces that are touching. All machines have moving parts and friction, so they have to use some of the work that is applied to them to overcome friction. This makes all machines less than 100 percent efficient. Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower than simple machines. When a compound machine consists of many simple machines, friction can become a serious problem, and it may produce a lot of . Lubricants such as oil or grease may be used to coat the moving parts of a machine so they slide over each other more easily. This is how friction is reduced in a car engine.
    ::所有机器都有移动部件和摩擦,因此它们必须使用一些应用到它们身上的工程来克服摩擦。这使得所有机器的效率都低于100%。由于复合机器的移动部件比简单的机器多,因此它们通常有更多的摩擦需要克服。因此,复合机器的摩擦往往比简单的机器要少。当复合机器由许多简单的机器组成时,摩擦会成为一个严重问题,并可能产生很多问题。油或油脂等润滑剂可以用来涂上机器的移动部件,这样它们就能更容易地滑过对方。这就是汽车引擎的摩擦减少的方式。

    Mechanical Advantage of Compound Machines
    ::复合机的机械优势

    The of a machine is the factor by which it changes the force applied to the machine. Many machines increase the force applied to them, and this is how they make work easier. Compound machines tend to have a greater mechanical advantage than simple machines. That's because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater its mechanical advantage tends to be.
    ::机器是改变机器所应用的力的因素。 许多机器增加了对机器应用的力力, 这就是如何使机器更容易工作。 复合机器比简单的机器更具有机械优势。 这是因为复合机器的机械优势等于其所有部件简单机器的机械优势。 它所装的简单机器越多,机械优势就越大。

    Q : Assume that the lever and the wheel and axle of a wheelbarrow each have a mechanical advantage of 2. What is the mechanical advantage of the wheelbarrow?
    ::问题:假设一个手推车的杠杆和轮轴和轴的机械优势是2。 手推车的机械优势是什么?

    A : The mechanical advantage of the wheelbarrow is the product of the mechanical advantage of the lever (2) and the mechanical advantage of the wheel and axle (2). Therefore, the wheelbarrow has a mechanical advantage of 4.
    ::A:手推车的机械优势是杠杆(2)的机械优势和方向盘和轴(2)的机械优势。 因此,手推车的机械优势是4。

    Summary
    ::摘要

    • A compound machine is a machine that consists of more than one simple machine.
      ::复合机器是一台由不止一台简单机器组成的机器。
    • Compound machines such as a wheelbarrow or corkscrew consist of just two simple machines. Big compound machines such as cars consist of hundreds or thousands of simple machines.
      ::汽车等大型复合机器由数百或数千台简单机器组成。
    • Compared with simple machines, compound machines generally have lower efficiency but greater mechanical advantage.
      ::与简单的机器相比,复合机械一般效率较低,但机械优势更大。

    Review
    ::回顾

    1. What is a compound machine?
      ::什么是复合机器?
    2. What simple machines are found in a wheelbarrow? How do they make it easier to carry heavy objects?
      ::在手推车上发现什么简单的机器?它们如何使携带重物更加容易?
    3. A pair of scissors is an example of a compound machine. Label the simple machines in the pair of scissors in the Figure .
      ::一对剪刀是复合机器的一个例子。

    A pair of blue-handled scissors, showcasing the cutting blades and pivot point.

    1. Why do compound machines tend to have lower efficiency but greater mechanical advantage than simple machines?
      ::为什么复合机械比简单的机器更效率低,但机械优势更大?