通常液体流、电子流、光子流、气体流等被广义地视为“流体”,其中电子流、光子流、气体流可统称为粒子流.对于液体流,常选取质量为!m的液柱作为研究对象;对于粒子流,通常是以体积元!V=!t·v·S的体积内的N个粒子为研究对象,从而将其转化成动量问题加以处理.下面就“流体类”问 Generally, liquid flow, electron flow, photon flow, gas flow, etc. are broadly considered as “fluids”, in which electron flow, photon flow, and gas flow can be collectively referred to as particle flow. For liquid flow, liquid columns of mass !m are often selected. As a research object, for the particle flow, it is usually the N particles in the volume of the volume element !V=!t·v·S as the object of study, so that it can be converted into a momentum problem to be dealt with. The following “fluid” question