The pressure of a gas is then a measure of the linear momentum of the molecules of a gas. Scalar Quantity Let us look at a gas that does not appear to move or flow. If we enclose the gas within a container, we will detect a pressure in the gas from the molecules colliding with the walls of our container. Therefore, pressure is a scalar quantity, not a vector quantity. It has a magnitude but no direction associated with it.
Pressure acts in all directions at a point inside a gas.
At the surface of a gas, the pressure force acts perpendicular to the surface. A force is applied to the top of the box. The pressure force within the box opposes the applied force. And the pressure equals the external force divided by the area of the top of the box. Inside the gas, the pressure acts in all directions.