1.General Equilibrium Conditions of A System （力系的一般平衡条件）According to Newton’s first law,the sum of the forces exerted on a body at rest must be zero. Notice, however, that this law says nothing about the moments, or rotational effects, of the forces. Clearly, the total moment must also be zero, else the body would rotate.根据牛顿第一定律，施加在一个静止物体上的力系的合力一定为零。
然而，请注意这个定律对力矩或力系的转动效应只字未提。
显然，合力矩也一定为零，否则物体将会转动。
We shall say that the system is in equilibrium if each particle within it is in equilibrium.如果系统内的每一个质点处于平衡，我们就可以说系统是平衡的。
2.stress and strain（应力和应变）Mechanics of materials is a branch of applied mechanics that deals with the behavior of solid bodies subjected to various types of roading.This field of study is known by several names,including"strength of materials"and"mechanics of deformable bodies." The solid bodies considered in this book include axially loaded members,shafts in rorsion,thin shells,beams,and columns,as well as rhe deterination of these ually the produced by the loads.If these quantities can be found for all values of load up to the failure load,then we will have a comple picture of the mechanics behavior of the body.材料力学是应用力学的一个分支，涉及受不同类型载荷的固体的性能。
这是一个有多种名称的研究领域，包括：“材料强度”，“易变形体的力学”。
本书中研究的固体包括受轴向载荷的杆，轴，梁，圆柱和由这些零件装配的机构。
一般情况下，我们研究的目的是测定因受载而引起的应力，应变和变形；如果当所有负荷量达到破坏载荷时，能够测得这些物理量，我们就可能得到一份完整的固体力学性能图。
3.A necessary condition for Eq.(1.3) to be valid is that the stress σmust be uniform over the cross section of the bar. This condition will be realized if the axial force P acts through the centroid of the cross section,as can be demonstrated by statics. When the load P does not act at the centroid ,bending of the bar will result ,and a more complicated analysis is necessary .Throughout this book ,however ,it is assumed that all axial forces are applied at the centroid of the cross section unless specifically stated to the contrary.Also,unless stated otherwise ,it is generally assumed that the weight of the object itself is neglected,as was done when discussing the bar in Fig.1.4.方程（1.3）的必要条件是应力 必须均匀分布在杆的横截面上。
如果轴向力通过截面的质心时，这个条件将会被认识，同时可以通过静力学验证。
当载荷P不是作用在行心时，将会产生挠度，更复杂的分析就是必要的了。
然而，如果没有特殊说明，本书中假定所有的轴向力都作用在横截面的行心。
而且，除非另有说明，物体本身的质量一般忽略不计，就像讨论图1.4中的杆那样。
4.Metals（金属）About three-quarters of the elements available can be classified as metals,and about half of these are of at least some industrial or commercial importance.Although the word metal,by strict definition,is limited to the pure metal elements ,common usage gives it wider scope to include metal alloys.While pure metallic elements have a broad range of properties ,they are quite limited in commercial use. Metal alloys ,which are combinations of two or more elements ,are far more versatile and for this reason are the form in which most metals are used by industry.大约现有元素中的四分之三可归类为金属；而大约一半金属元素都有一定的工业或商业上的重要性。
尽管严格定义的金属只局限于纯金属，但是普遍的用法是把它扩展到更广范围的金属合金。
尽管纯金属有很多特性，他们在商业中的应用也很局限。
金属合金由两种或两种以上的元素组成，用途非常广泛，正是由于这种结构上的原因，很多金属被用于工业上。
金属材料是晶状固体。
单个晶体是由单元晶粒按有规则模式重复而形成的三维晶格。
一块金属则是成千上万相联晶体的集合体，而这些晶粒都沉浸在从晶体原子中脱离出来的带负电的价电子云中。
由于这些自由电子对带正电的金属原子或离子有静电吸引力，因此可以将晶体结构紧凑的结合在一起。
而由于金属结晶结构致密本质导致的这种很大的结合力是造成金属一般都具有良好机械性质的原因。
同样，电子云使大多数金属有很好的导电性和导热性。
5.Copper alloys are the second nonferrous material in terms of consumption.There are two major groups of copper alloys:brass,which is basically a binary-alloy system of copper and zinc ,and bronze ,which wasoriginally a copper-tin alloy system.Today,the bronzes include other copper-alloy systems.从消耗量方面来说，铜合金是排在第二位的有色金属。
铜合金有两大类：一类是黄铜，它是以铜和锌为基础的二元合金；另一类是青铜，它原本是铜锡合金系统。
而现在，青铜还包含其他铜合金系统。
6.Chemical Engineering(化学工程，化工)In a wider sense, engineering may be defined as a scientific presentation of the techniques and facilities used in a particular industry. For example, mechanical engineering refers to the techniques and facilities employed to make machines. It is predominantly based on mechanical forces which are used to change the appearance and/or physical properties of the materials being worked, while their chemical properties are left unchanged. Chemical engineering encompasses the chemical processing of raw materials, based on chemical and physico-chemical phenomena of high complexity.从广义上讲，工程被定义为特定行业使用的科学技术和设施，例如，机械工程是指技术和设施被用来制造及其，它（机械工程）主要是以机械力基础，这些力用于改变被加工材料的表面形状或物理性质，而材料的化学性质不变。
化学工程包括材料的化学加工，主要以化学和物理化学的高度复杂性为基础。
7.Thus,future chemical engineers will conceive and rigorously solve problems on a continuum of scales ranging from microscope to macroscale.They will bring new tools and insights to research and practice from other disciplines: molecular biology,chemistry,solid-state physics,materials science,and electrical engineering.And they will make increasing use of computers,artificial intelligence,and expert system in problem solving,in product and process design,and in manufacturing.如此，将来化学工程将会构想和在微观到宏观的连续的尺度范围内严谨的解决问题。