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对单个物体的讨论,宜用两大定理,涉及时间(或研究力的瞬间作用)优先考虑动量定理,涉及位移优先考虑动能定理;对多个物体组成的系统讨论,则优先考虑两大守恒定律;涉及加速度的力学问题必定得用牛顿第二定律,必要时再用运动学公式。1.动力学观点:包括牛顿三大定律和运动学规律;2.动量观点:包括动量定理和动量守恒定律;3.能量观点:包括动能定理和能量守恒定律。注意:洛仑兹力和速度方向垂直,永不做功;重力G对物体做功与路径无关,只取决于初、末位置的高度差;电场力F对电荷做功与路径无关,只取决于初末位置的电势差。例1如图1所示,套在很长的绝缘直棒上
For the discussion of a single object, it is appropriate to use two major theorems, which give priority to the momentum theorem in time (or the momentary effect of the research force), and prioritize the kinetic energy theorem in relation to the displacement. For the systematic discussion of the composition of multiple objects, the two conservation laws are prioritized Mechanics involving acceleration must use Newton’s second law and, if necessary, kinematics. 1. Kinetic point of view: including Newton’s three laws and kinematic laws; 2. Momentum point of view: including the law of momentum and conservation of momentum; 3. Energy point of view: including the kinetic energy law and the law of conservation of energy. Note: Lorentz force and velocity direction perpendicular, never work; gravity G work on the object has nothing to do with the path, only depends on the height difference between the initial position and the end position; electric field force F has nothing to do with the electric charge and the path, only depends on the initial and final Potential difference in position. Example 1 Shown in Figure 1, set in a very long straight rod insulation