物理学专业英语翻译.docx

2.1 Introduction(引言) We begin our study of the physical universe by examining objects in motion. Thestudy of motion . whose measurement. more than 400 years ago gave birth to physics. iscalled kinematics. Much of our understanding of nature comes from observing the motion of objects. Inthis chapter we will develop a description for the motion of a single point as it movesthrough space. Although a point is a geometrical concept quite different from everydayobjects such as footballs and automobiles, we shall see that the actual mot10n of manyobjects is most easily described as the motion of a single point (the center of mass). plusthe rotation of the object about that point. Postponing a discussion of rotation. let usbegin he-re with a description of a single point as it moves through space. Space and timeKinematics is concerned with two basic questions. Where? and When?. Thoughthe questions are simple. the answers are potentially quite complicated if we inquire aboutphenomena outside our ordinary daily experiences. For example. the physics of very highspeeds, or of events involving intergalactic distances or submicroscopic dimensions. isquite different from our common-sense ideas. We will discuss the interesting subjects inlater chapters. For the present we shall adopt the space and time of Newton-thoseconcepts we gradually developed as a result of our everyday experiences. Space is assumed to be continuously uniform and isotropic. These two terms meanthat space has no graininess and that whatever its properties may be, they areindependent of any particular direction or location. in the words of Isaac Newton. Absolute space . in its own nature . without relation to anything external . remains alwayssimilar and unmovable. Every object in the universe exists at a particular location in space. and an object may change its location Ly moving through space as time goes on. Wespecify the Location of a particular point in space by its relation to a frame of reference. Time, according to Newton, is also absolute in the sense that it flows on at a uniform rate . We cannot speed it up or slow it down in any way. in Newtons words, Absolute. true. and mathematical time . of itself . and from its own nature . flows equably without relation to anything external. and by another name is called duration. Time isassumed to be continuous and ever advancing. as might be indicated by a clock. Space and time are wholly independent of each other. though it is recognized that allphysical objects must exist simultaneously in both space and time. Remarkably . many of these traditional ideas turn out to be naive and inconsistent withexperimental evidence. The world is just different from the picture we form from our common-sense. intuitive ideas. Space and time, by themselves. arc concepts that arc difficult (or perhaps impossible) to define in terms of anything simpler. However. we can measure space and time in unambiguous ways. We define certain operations by which we obtain numerical measurements of these quantities using rulers and clocks. based upon standard units of space and time. For many years. our standard of time was based on astronomical observations of the earths rotation. Because of the variations in the earths rotation . in 1967 the 13th General Conference on Weights and Measures. attended by 38 nations. adopted an atomic standard for time. Similarly. our former standard of length was the distance between two marks on platinum-iridium bar. kept at Sevres. France. in 1960. the fundamental length standard was redefined in terms of the wavelength of light emitted during a transition between two. The standard units of time and length may be described as follows: An interval of time. The fundamental unit is the second (s) . which by international agreement is defined as the duration of 9 192 631 770 periods of radiation corresponding to the transition between the two lowest energy levels in the atomic isotope cesium 133. An interval of length. The fundamental unit is the meter (m). which is defined independently of the time interval Before 1983 . by international agreement the meter was defined as exactly 1 650 763. 73 wavelengths of the orange light emitted from the isotope krypton 86. in November 1983. the length standard was defined as the distance that light travels in a vacuum in l1299 792 458 second. l angstrom(A) -. 10-l0 m l micron (u or um)10-6 m2.1简介（引言）我们开始研究宇宙的物理研究物体的运动。本运动研究。其测量。400多年前，诞生了物理学。是称为运动学。我们的许多认识自然来观察物体的运动。在这一章我们将开发一个描述运动的一个单点移动通过空间。虽然是一个几何概念完全不同的生活对象，如足球和汽车，我们应看到，实际运动许多对象是最容易被描述为一个单一的运动点（“质心”）。加上对象的旋转这一点。推迟讨论旋转。让我们一开始he-re描述单点它通过移动空间。时间和空间运动学是有关的基本问题。”在哪儿。什么时候。虽然。问题很简单。答案可能是相当复杂的，如果我们探询在我们的日常经验现象。比如说呢。物理非常高速度，或事件涉及星际距离或微观层面。是完全不同于我们的常识。我们将讨论有趣的科目后面的章节。目前我们所应采取的时间和空间的牛顿概念逐渐导致了我们的日常经验。空间被认为是连续均匀和各向同性。这些术语的意思空间没有“粒度”，无论其性质可能是，他们是独立于任何特定的方向或位置。在对艾萨克词的牛顿。绝对空间。其本身性质。没有与任何外部。永远保持相似及不动的。”每一个物体在宇宙中存在，在某一特定位置空间。和对象可以改变其位置的移动通过空间随着时间的流逝。我们指定的位置，一个特定的点在空间的关系参考框架。同时，根据牛顿，也是绝对的意义上说，它“流”在均匀速率。我们不能加快或者减慢以任何方式。在牛顿的话，瑞典伏特加。真的。和数学的时间。本身。从其本身的性质。均匀流动没有与任何外部。和另一个名字叫时间。”时间是假定连续不断进步。可能是由一个时钟。时间和空间是完全相互独立的。虽然它是公认的，所有的物理对象必须同时存在于空间和时间。值得注意的。许多这些传统的想法是幼稚和不符合实验证据。世界只是从不同的图片从我们常识的。直观的想法。空间和时间，由自己。弧，弧的概念困难（或不可能）定义在任何事情更简单。然而。我们可以测量时间和空间明确的办法。我们定义的某些操作得到的数值测量这些数量使用统治者和钟表。基础上标准单位的时间和空间。许多年。我们的标准时间是根据天文观测的地球旋转的。由于地球自转变化。1967第十三届大会上度量衡。参加了38个国家。采用原子标准时间。同样的。我