理论力学动量定律14.ppt

1 Discussion (1) Appling the law of conservation of linear momentum plus the theorem of the change in kinetic energy solve a problem . (2) Making use of the relation of kinematics of plane motion when computing kinetic energy ,Theorem of conservation of the total angular momentum with respect to the center of mass of a system + theorem of the change in kinetic energy +theorem of the change in angular momentum +theorem of motion of center of mass. ,we may calculate by differentiating the expression of the theorem of the change in kinetic energy in integral form with respect to time t ,but noting to analyze the motion of rod AB in an arbitrary position. Example 4 . Calculate a few basic quantities (linear momentum ,angular momentum and kinetic energy) 解：（1）取圆盘为研究对象 Solution: (1) Take the disc as the object under study. ，圆盘平动。 , the disc is in translational motion. (2)Applying the theorem of the change in kinetic energy determine the velocity of point B. . （2）用动能定理求速度。 Considerate the whole system. At the initial moment . 取系统研究。初始时T1=0 ， At the lowest position 最低位置时： 代入数据，得 Substituting the known values into this expression we get . (3) Applying the theorem of the change in angular momentum determine the angular acceleration . （3）用动量矩定理求杆的角加速度? 。 ?＝0. The acceleration of the center of the disc is The acceleration of the center of mass of the rod is 杆质心 C的加速度： 盘质心加速度： （4）由质心运动定理求支座反力。研究整个系统。 (4) Calculate the reaction force at mount A from the theorem of the motion of the center of mass. Investigate the whole system. . 代入数据，得 Substituting the known values into this expression we get . Using the theorem of the conservation of the total angular momentum with respect to the center of mass of a system plus the theorem of the change in kinetic energy plus the theorem of the change in angular momentum plus the theorem of motion of