外界作用改变物体的运动状态,这是力学的主题思想.由于运动的多样性,我们要引入多种描述物体运动的物理量和表示对物体作用的物理量.初中物理表示作用的量主要有力、压强、力与力臂的乘积(即力矩)、功等.在学习时,要根据具体的物体的运动情况分析对物体作用的量,找到解决问题的途径. Due to the diversity of sports, we need to introduce a variety of physical quantities that describe the movement of the object and the physical quantities that represent the effect on the object. The quantity of the physical representation of the junior middle school is mainly the force, the pressure, The product of the force and the arm of force (ie moment), work, etc. In learning, according to the specific object movement analysis of the role of the object to find the solution to the problem.