科技英语力学部分课件.pptVIP

Part One Mechanics; The fact that if we choose different body as the reference to describe the same motion of a given object, the indications will be different, is called the relativity of the description and measurement of the motion. The particular body that serves as a reference chosen by the observer is defined as the frame of reference. ; It is usually pictured by means of a coordinate system, consisting three mutually perpendicular axes -X, -Y and Z-axes, and relative to it the position, velocity, acceleration and orbit of the moving object can be quantitatively specified. Particle is an ideal model used to simplify an object and to describe its motion. We can represent an object as a particle if every part of it moves in exactly the same way so that we can regard it as a mass point with no size and no shape. Translational motion -- the change of the position of the particle as a function of time will give a complete description of the motion for the given object. ;POSITION VECTOR AND DISPLACEMENT: The position of a particle in space is a vector given by in a rectangular coordinate system. ; The position vector as a function of time can determine the location of a particle at any given time. It is called position function and given by Its three component equations are written by the following scalar functions ;Mechanical motion 机械运动 Rectilinear motion 直线运动 curvilinear motion 曲线运动 Circular motion 圆周运动 Uniform circular motion 匀速圆周运动; frame of reference 参考系； coordinate system 坐标系； Cartesian coordinate system 直角坐标系; the nature coordinate system 自然坐标系； Particle 质点； position vector 位置矢量（位矢）； displacement 位移； Velocity 速度; averge velocity 平均速度; instantaneous velocity 瞬时速度； acceleration 加速度; the tangential acceleration; 切向加速度； the normal acceleration 法向加速度； circular motion 圆周运动;; rigid body 刚体； torque 力矩； axis of rotation 旋转轴； th