In a hydraulic press, what happens to the output force when the output piston area increases?

• A. The output force increases
• B. The output force decreases
• C. The fluid pressure increases
• D. The input force increases

Answer: (A)

Pascal's law tells us that pressure in a confined, incompressible fluid is transmitted equally throughout the system. The output force is the pressure times the output piston area, F_out = P × A_out. If you keep the same pressure (set by the input force and input piston area), increasing the output piston area makes F_out larger in direct proportion to that area. In other words, you can multiply the force at the output by using a larger output area, though you trade off distance (the movement of the output piston) for that extra force. So the output force increases when the output area increases. The fluid pressure does not automatically rise just because the area increases, and you don’t necessarily need to increase the input force to get more output force.