摩擦力总是做负功吗临洮县二中学生赵国梁指导教师张镇江摩擦力是宏观领域中的一种实物接触力。由于它具有相互性，所以属牛顿力。当两物体在接触面的法线方向互相挤压，而在接触面的切线方向有相对运动或相对运动的趋势时，便在接触面上产生阻碍这种运动或运动趋势的力。... Does friction always do negative work? Lin Guoxian secondary school student Zhao Guoliang instructor Zhang Zhenjiang’s friction is a kind of physical contact in the macro field. Because of its reciprocity, it is Newtonian. When two objects are pressed against each other in the normal direction of the contact surface and there is a tendency of relative movement or relative movement in the tangential direction of the contact surface, a force that impedes the movement or movement tendency is generated on the contact surface. ...