主动力信息足以确定静摩擦力的指向吗?  

CAN THE POINTING DIRECTION OF STATIC FRICTION BE UNIQUELY DETERMINED BY THE INFORMATION OF ACTIVE FORCES?

作　　者：陈奎孚[1] 姚海蓉[2] 张云文[2] CHEN Kuifu;YAO Hairong;ZHANG Yunwen(College of Science;College of Engineering,China Agricultural University,Beijing 100083)

机构地区：[1]中国农业大学理学院,北京100083 [2]中国农业大学工学院,北京100083

出　　处：《物理与工程》2018年第4期39-44,共6页Physics and Engineering

摘　　要：摩擦力既是教学的重点,更是教学的难点,特别是静摩擦力的指向确定。文章将阐述:首先,就计算而言,静摩擦力指向确定并不重要;第二,对某些动力学问题,主动力信息不足以唯一确定静摩擦力的指向;第三,在某些特殊条件下,比如运动刚体的质心位于接触点法线上(如无质量偏心的圆柱),由主动力向撞击中心简化的主矩可确定静摩擦力的指向;第四,把摩擦面假想成光滑面后,运动刚体在接触点的切向加速度指向与该处静摩擦力的指向相反。The concept of frictional force is essential both in physics and theoretical mechanics,while determining the pointing direction of static friction（PDoSF）is a challenge to students.We will expound that,firstly,as far as computing the frictional force,the PDoSF should not be overemphasized.Secondly,the PDoSF can not be uniquely determined by the information of active forces for some dynamical problems.Thirdly,with some specific constraints,for example,the mass center of the moving rigid body lies on the normal line passing the frictional point（a familiar case is a disk with its mass uniformly distributed）,the PDoSF can be uniquely determined by the principal moment with respect to the center of percussion,and the PDoSF should endow the static friction with the potential to balance the principle moment.Fourthly,assuming that only the frictional interface is replaced by a frictionless one（all the active forces and the angular velocity are kept）,then the PDoSF is opposite to the acceleration direction of the contacting point on the moving rigid body.

关 键 词：静摩擦力 受力分析 受力图 达朗贝尔原理 撞击中心 

分 类 号：G634.7[文化科学—教育学]