The intensity of the flux of particles is assumed to be the same in all directions, so an isolated object A is struck equally from all sides, resulting in only an inward-directed pressure but no net directional force.
The intensity of the flux of particles is assumed to be the same, effected by a penetration of masses in all directions finally stopped by molecules. So an isolated object A is struck equally from all sides, resulting in only an inward-directed pressure but no net directional force.