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易错知识点一判断力是否做功做功的两个必要因素:作用在物体上的力和物体在力的方向上移动的距离。常见的不做功的情形有:①“劳而无功”是指物体受到力的作用,也移动了一定距离,但物体运动方向与所研究力的方向垂直,如沿斜面下滑的木块所受支持力对木块不做功。②“不劳无功”是指物体虽然移动了一定距离但是在运动方向上不受力,如吊车吊起货物在水平方向移动、木块由于惯性在光滑水平地面上滑行等。③“不动无功”是指物体虽然受到力的作用但没有沿力的方向移动一定的距离,如推而未动、搬而未起等。
The two necessary factors to judge whether a work is done or not are: the force acting on the object and the distance the object moves in the direction of the force. The common case of not doing work are as follows: ① “Work without power” means that the object is subjected to force and moves a certain distance, but the object’s movement direction is perpendicular to the direction of the force under study, The supportive force does not work on wood. ② “Inferior labor ” means that although the object has moved a certain distance but not in the direction of movement, such as crane lifting cargo moving in the horizontal direction, the block due to inertia glides on a smooth horizontal ground and so on. ③ “Fixed Reactive ” refers to the object although the role of the force but not along the direction of the force to move a certain distance, such as pushing without moving, moving without equal.