摩擦力的方向一定与相对运动的方向相反,或与相对运动趋势的方向相反,但摩擦力的方向不一定与物体的运动方向相反.摩擦力的方向与物体的运动方向可能相同,滑动摩擦力的方向总是与物体“相对运动”的方向相反.所谓相对运动方向,即是把与研究对象接触的物体作为参照物,研究对象相对该参照物运动的方向.当研究对象参与几种运动时,相对运动方向应是相对接触 The direction of friction must be the opposite of the direction of relative movement or opposite to the direction of relative movement, but the direction of friction may not be opposite to that of object. The direction of friction may be the same as the direction of object movement, and the sliding friction The direction of the object is always the opposite of the object relative movement direction, that is, the object in contact with the object of study as a reference to study the direction of the object relative to the reference object movement when the study participants in several During exercise, the relative movement direction should be relative contact