I am informed that the pressure is due to the collision of particles on the surface.If so on the surface of water in a glass, the air particles could collide to water surface in many different directions and not just normal to the surface.So how can we say pressure if Force normal to surface divided by area?.Even if it is a definintion of force.What is the parallel(horizontal component) doing to the water surface (definitely not moving water in hydrostatics).
Am I missing something here?.