Pascal's law is based on the transmission of pressure uniformly. It states that the pressure applied to an enclosed fluid is transmitted undiminished throughout the fluid and to the walls of the container. If you increase the pressure \(P_0\) on the surface of the fluid in Figure 3, the pressure at any depth \(h\) should increase by the same amount and also to the walls of the container.
One example of Pascal's law is shown in Figure 1. The pressure applied to the piston of small area \(A_1\) is transmitted undiminished to every point in the fluid and also to the piston of large area \(A_2\).
Note that the same pressure is transmitted to the walls of the container as well.
The pressure \(P_1\) on the piston of area \(A_1\) due to the force \(F_1\) is \(P_1 = F_1/A_1\) and the pressure \(P_2\) on the piston of area \(A_2\) due to the force \(F_2\) is \(P_2 = F_2/A_2\). Since both pistons are in the same level, the pressure in both pistons should be the same that is, \(F_1/A_1 = F_2/A_2\). And the force on the piston of the larger area \(A_2\) is
\[{F_2} = \frac{{{A_2}}}{{{A_1}}}{F_1}\]
We know \(A_2>A_1\) and the force \(F_2\) is greater than \(F_1\). It means the force \(F_1\) is magnified to \(F_2\) and became able to support the car as in Figure 4. Note that by Newton's third law the car also exerts the downward force of magnitude \(F_2\).
