再如跳水运动员的团身展体动作解读.pptx

Angular Momentum;1. Kepler’s laws ;;;For any motion caused by any force , the following equation is always correct : ;Example 1 An object of mass m moves in a circle of radius R with a constant speed v . What is its angular momentum ? ;Example 3 A particle of mass m moves with constant velocity v along a straight line which is a distance b from the origin of a coordinate system . (a) Find the angular momentum of the particle at any instant about point o . (b) Show explicitly that the angular momentum is conserved . (c) Calculate the angular momentum about point P .;;3. Torque and angular momentum;Example 4 A force of 15.0N acts on the particle Shown . Compute the torque acting on the particle with respect to (a) point A , (b) point B .;Example 5 An ice skater holds two heavy masses , each of mass 8.0kg . Originally the skater is rotating at an angular speed of 2rad/s with the masses 0.4m from the axis of rotation . What will be the skater’s angular speed if the masses are pulled in to a distance of 0.3m ?;再如：跳水运动员的“团身--展体”动作;例6、如图示，光滑的水平桌面上有一小物体，一条细绳的一端联结此物体，另一端穿过桌子上的小孔。物体原来以一定的角速度在桌面上以小孔为圆心作圆周运动，在小孔下方缓慢地往下拉绳的过程中，物体的动量、动能以及对小孔的角支量是否变化？为什么？;4. Vortices and firestorms ;;;例.一质量为m、长为a、宽为b的均匀薄木板可绕oo轴自由转动，则其转动惯量是 ；若用一质量亦为m的泥团以初速度v垂直木板面撞在开始时静止的木板的边缘并粘在上面，则系统的角速度是 。 ;例、在工程上，两个轴线在中心连线上的飞轮A和B，常用摩擦啮合器C使它们以相同的转速一起转动，如图所示。设A轮的转动惯量为JA=10kg·m2，B轮的转动惯量为JB=20kg·m2，开始时A轮的转速为900rev/min，B轮静止。求：两轮对心啮合后的共同转速。