The Concepts of Mass

物理学の基礎概念の理解の目的で,古典力学における質量概念について,ガリレイ,ニュートン以降,質量の定義と慣性質量の動力学的意味について調べた。ニュートンのプリンキピア中の,運動の法則2について,原典に準拠した解釈を行い,それにもとづいた慣性質量の動力学的定義を示した。さらに,相対論的力学では,質量が速さによって変わることに起因して,ニュートンでは同じであった,"物質の量"としての質量と,動力学的慣性質量とが異った大きさになる場合があること,および,慣性質量が粒子の運動方向によって,大きさを異にすることを指摘した。With a view to understand the basic concepts of physics, the author engaged in research of the concepts of mass in classical dynamics. Especially, the definition of mass as well as the dynamical meaning of inertial mass was investigated historically from the thoughts of G. Galilei and I. Newton. The author gave an interpretation in connection with the 2nd law of motion in Newton's Principia, being based on the original. Resting on this interpretation, he showed the dynamical definition of inertial mass. Further, the author pointed out the following facts as to the concepts of mass in relastivistic dynamics. The mass as a material quantity was same magnitude with the inertial mass in the case of Newton. However, being caused by velocity-dependency of the magnitude of mass in the relastivistic dynamics, it takes place in certain cases that the mass as a material quantity becomes different magnitude from the inertial mass. The inertial mass shows different magnitudes subject to the direction of the motion of a particle