机械工程专业英语教程翻译 第3版 施平 lesson1

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Lesson 1  Basic Concepts in Mechanics

第1课 力学基本概念

    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、时间和作用力做出科学分析的分支称为力学。它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因素，动力学对随时间而变化的系统进行分析。

    Forces are transmitted into machine members through mating surfaces, e. g., from a gear to a shaft or from one gear through meshing teeth to another gear, from a V belt to a pulley, or from a cam to a follower.

    力通过配合表面传到机器中的各构件上。例如，从齿轮传到轴或者从齿轮通过啮合的轮齿传到另一个齿轮，从V带传到带轮，或者从凸轮传到从动件。

    If the forces between gear teeth are too large, the oil film may be squeezed out from between them. This could result in flaking and spalling of the metal, noise, rough motion, and eventual failure.

    如果齿轮间相啮合的齿与齿之间的力过大，就会将油膜从齿间挤压出来。这会造成金属的碎裂和剥落，噪音增大，运动不精确，直至报废。

    Two equal and opposite forces acting along two non-coincident parallel straight lines in a body cannot be combined to obtain a single resultant force. 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.

    沿两条不重合平行线作用在同一个物体上的两个大小相等, 方向相反的力不能被合并成一个合力。作用在一个物体上的两个这样的力构成一个力偶。这两条作用线之间的垂直距离是力偶臂，力偶面是包含这两条作用线的
平面。

    Mechanics deals 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.

    力学涉及到两种类型的量：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，矢量既有大小又有方向。矢量的例子有位移，速度，加速度，力，力矩和
动量。

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