抄録
Linear equation of motion consists of mass, stiffness and viscosity, and is deduced from the energy law. Functions of mass and stiffness are clearly explained by the law of conservation of mechanical energy. But usually, it is said that viscosity can not be explained by the energy law. In this paper first, relation between viscosity and potential energy is made evident. Second, generation mechanism of viscosity is made clear from the standpoint of nuclear physics.It is newly introduced that the inflect point of Lennard -Jones potential decides the boundary between the elastic and the viscous regions. Third, the reason is presented why viscosity dissipates mechanical energy by changing it to thermal energy. Forth, it is made clear how viscosity yields the resistance force proportional to given velocity.
