Question

Consider a table that measures 1.5m

Answer 1

(a) P = F/A, so you can calculate the force by reordering the equation:

F = PA

where P is = 1 atmosphere = 101,325 Pascal or N/m^2

(b) The total force acting upward from the bottom of the table is the same as the answer in (a). This is because the pressure we experience is equal from all sides, or else the table would be crushed flat.

Another way of explaining this is this:

Pressure is a scalar quantity, not a vector quantity.

In a static gas, the gas as a whole does not appear to move. The individual molecules of the gas, however, are in constant random motion. Because we are dealing with an extremely large number of molecules and because the motion of the individual molecules is random in every direction, we do not detect any motion. If we enclose the gas within a container, we detect a pressure in the gas from the molecules colliding with the walls of our container. We can put the walls of our container anywhere inside the gas, and the force per unit area (the pressure) is the same. We can shrink the size of our "container" down to an infinitely small point, and the pressure has a single value at that point. 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.