被动力是相对于主动力而言的.主动力的大小与方向由其本身的性质决定,与物体是否受其它的力的作用无关;与物体作何种性质的运动无关,如重力、电场力等.被动力则由主动力与物体的运动性质共同决定,如弹力、摩擦力等.它们通常要借助物理规律,根据物体的运动性质建立与主动力的 Passive force is relative to the main motive force, the size and direction of the motive force is determined by its own nature, regardless of whether the object is affected by other forces or not, and the nature of the object, such as gravity, electric field force Etc. Passive force is determined by the motive force and the nature of the movement of the object, such as elasticity, friction, etc. They are usually based on physical laws, according to the nature of the movement of the object to establish and motivate