动量定理是力学的重要定理之一,它反映的是力的持续作用效果和规律.在解决作用时间短、作用力大而且随时间变化的碰撞、冲击等问题时,动量定理显得比牛顿定律更为简捷.一般涉及运动的两个状态和时间时常用动量定理.即使如此,在遇到复杂的物理问题,应用动量定理处理时,仍然存在着解题技巧问题.那更是好上加好.一、巧用微元法化难为易动量定理表达式Ft=m△υ中的m为常量.倘若是个变量问题,直接应用定理有难度.为此,我们巧取物体的某一部分或增加的质量为研究对象,将逐渐变化的质量在一段很短时间看作定质量.采用质量微元研究,便可将难题化易.例1.一个迎面截面积为50米~2、初速度为10干米/秒的宇宙飞船在飞行中进入宇宙尘埃区域,该区域的尘埃密度p为2.0×10~(-4)千克/米~3,为了使飞船的速度不改变,推力F应增加多少?(飞船与尘埃的碰撞是完全非 The momentum theorem is one of the important theorems of mechanics. It reflects the continuous effects and laws of force. When solving problems such as short acting time, large force and time-dependent collision and impact, the momentum theorem appears to be more than Newton’s law. For the sake of simplicity, the momentum theorem is commonly used when two states and time of motion are involved. Even so, when dealing with complex physical problems and applying the theorem of momentum, there are still problem solving techniques. It is even better. First, the use of micro-elements is difficult to be easy momentum theorem expression Ft = m △ υ m is a constant. If it is a variable problem, it is difficult to directly apply the theorem. To this end, we cleverly take a part of the object or increase the quality For the research object, the gradual change of quality is regarded as a certain quality in a short period of time. Using quality micro-elements research, the problem can be easily solved. Example 1. A cross-sectional area of ​​50 meters to 2, the initial speed of 10 dry The m/s spacecraft enters the cosmic dust region during flight. The dust density p in this region is 2.0×10 -4 kg/m 3 . In order to keep the speed of the spacecraft unchanged, what is the thrust F increase? Collisions between spacecraft and dust are completely non-existent