Thrust is the force that acts in the upward direction on a submerged body. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction on that system. The force is called the thrust and it is applied on a surface in a direction perpendicular or normal to the surface. Thus, there is no component of thrust acting on the vertical sides, as the component of thrust will be parallel to the vertical sides.