pulleys
Lesson1 
1、the branch of scientific analysis， which deals with motions， time， and forces, is called mechanics and is made up of two parts, statics and dynamics. Statics deals with the analysis of stationary systems, i。e。, those in which time is not a factor, and dynamics deals with systems, which change with time。
对运动时间和作用力作出科学分析的分支成为力学。他由静力学和动力学两部分组成。静力学对静止系统进行分析，即在其中不考虑时间这个引述，动力学对事件而变化的系统进行分析.
2、Any two such forces acting on a body constitute a couple. The arm of the couple is the perpendicular distance between their lines of action， and the plane of the couple is the plane containing the two lines of action.
作用在一个刚体上的两个这样的的里构成一个力偶。力偶臂是这两个条作用线之间的垂直距离，力偶面是包含着两条作用线的平面。
3、Mechanics deal with two kinds of quantities： scalars and vectors. Scalar quantities are those with which a magnitude alone is associated。 Examples of scalar quantities in mechanics are time, volume, density， speed， energy， and mass. Vector quantities， on the other hand, possess direction as well as magnitude。 Examples of vectors are displacement, velocity， acceleration, force, moment， and momentum。
力学涉及两种类型的量，标量 和矢量。标量是那些只有大小的量。在力学中标量的例子有时间、体积、密度、速率、、能量和质量。另一方面，矢量既有大小又有大小又有方向。矢量的例子有位移、速度、加速度、力、力矩、动量.
Lesson2（此课后面没翻译，翻译的不太准确谅解)
1 、The turning of a part in a lathe is another example of several forces in action。（as shown in figure1） 
车床车削是一些力在起作用的另一个例子.figure1（如图)。
2 、If this workpiece is held between the centers of the lathe, the centers exert a compressi
ve force against the work。
如果这个工件在放在车床中心之间,中心车床对工作产生压力。
3、 Rotary motion is required to drill holes， turn parts in a lathe, mill surfaces， or drive a generator or fan belt.
扶轮运动需要去钻孔，在车床上转换两件,表面，或驱动发电机或风扇皮带
4 、Harmonic and Intermittent Motion（谐和运动和间歇运动）: Any simple vibration， such as the regular back， and forth movement of the end of a pendulum, is simple harmonic motion。
Lesson4
1 、Virtually all machines contain shafts。 The most common shape for shafts is circular and the cross section can be either solid or hollow.
实际上,几乎所有的机器中都装有轴。轴的最常见的形状是圆形，其截面可以是实心的，也可
以是空心的（空心轴可以减轻重量）。有时也采用矩形轴,例如，螺丝起子的头部。套筒扳手和控制旋钮的杆。
2、 A shaft must have adequate torisonal strength to transmit torque and not be over stressed it must also be torsional stiff enough so that one mounted component does not deviate excessively from its original angular position relative to a second component mounted on the same shaft。
为了在传递扭矩时不发生过载，轴应该有适当的抗扭强度。轴还应该具有足够的抗扭强度，以使在同一轴上的两个传动零件之间的相对转角不会过大.
3 、Components such as gears and pulleys are mounted on shafts by means of key. The design of the key and the corresponding keyway in the shaft must be properly evaluated。 For example, stress concentrations occur in shafts due to keyways， and the material removed to from the keyway further weakens the shaft。
齿轮和皮带轮等零件通过键连接在轴上.在键及轴上与之相对应的键槽的设计中，必须进行认
真的计算。例如，轴上的键槽会引起应力集中，由于键槽的存在会使轴的横截面积减小,会进一步减弱轴的强度。
4、Another important aspect of shaft design is the method of directly connecting one shaft to another. Devices such as rigid and flexible couplings accomplish this.
轴的设计工作中的另一个重要方面是一根轴与另一根轴之间的直接连接方法。这是由刚性或者弹性联轴器来实现的。
Lesson5
1、The term shaft usually refers to a relatively long member of round cross section that rotates and transmits power. One or more members such as gears  ，sprockers,pullys,and cams are usually attached to the shaft by means of pins, keys，splines，snap rings,and other devices 。 These latter members are among the "associated parts” consedered in this text,as ate couplings and universal joints , which serve to connect the shaft to the source of power or load。
2、It is apparent that shafts can be subjected to various combinations of axial，bending，and torsional loads,and that these loads may be static or fluctuating.
3、Torsional defection can affect the accuracy of a cam or gear driven mechanism .Furthermore,the greater the flexibility —either lateral or torsional—the lower the corresponding critical speed.
4、A gear can be gripped axially between a shoulder on the shaft and a spacer ,with torque being transmitted through a keyways。
Lesson7
1、Fasteners are devices which permit one part to be joined to a second part and ,hence,they are involved in almost all designs 。 The acceptability of any product depends not only on the selected components ， but also on the means by which they are fastened together. The principal purposes of fasteners are to provide the following design features；
紧固件是将一个零件与另一个零件进行连接的零件。因此，几乎在所有的设计中都要用到紧
固件。人们对于任何产品的满意程度不仅取决于其组成部件,还取决于其连接方式。
2、The importance of fasteners can be realized when referring ro any complex product，In the case of the automobile,there are literally thousands of parts which are fastened together to produce the total product。The failure or loosening of a single fastener could result in a simple nuisance such as a door rattle or in a serious situation such as a wheel coming off.

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