The frictional-collisional behavior of granular materials in motion under gravity is studied by using a continuum approach with a heuristic study on a collision mode. In a binary mode there are three basic mechanical motions, which are called kinetic, collisional, and frictional motion. They correspond to flying, contact, and friction time, respectively. Constitutive equations are then postulated with four constants, which are dispersive pressure, viscosity, thermal diffusivity, and collisional energy sink. The conservation laws for mass, momentum and energy are posed with the constitutive equations developed to study the granular flows on an inclined and in a vertical channel.