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Output force in a hydraulic system

Aviation Mechanic General (AMG) practice question 12 of 20 on Physics for Aviation. ACS element AM.I.J.K12 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONIn a simple two-piston hydraulic system, the output piston has 20 times the surface area of the input piston. Based on Pascal's law, how does the force generated at the output piston compare with the input force?

  1. AIt equals the input force, since pressure is the same everywhere
  2. BIt is one-twentieth of the input force
  3. CIt is 20 times the input force
Show the answer and explanation

Correct answer: C. It is 20 times the input force

  • A — incorrect The pressure is indeed the same everywhere, but force depends on pressure times area. A larger piston area produces a proportionally larger force.
  • B — incorrect The output piston moves one-twentieth as far as the input piston, but its force is 20 times greater, not smaller.
  • C — correct Pressure acts equally throughout the fluid, and Force = Pressure × Area. With 20 times the area at the same pressure, the output force is 20 times greater, giving a mechanical advantage of 20.

BACKGROUND

Pascal discovered that pressure set up in a fluid acts equally in all directions and at right angles to the containing surfaces. The relationship among the variables is Force = Pressure × Area, which can be rearranged to Pressure = Force ÷ Area and Area = Force ÷ Pressure. In a two-piston system, the pressure created by the input piston acts on the output piston, and because force equals pressure times area, a larger output piston produces a larger force. The ratio of output force to input force is the mechanical advantage. No work is gained, however: if force is multiplied by 20, the output piston moves only one-twentieth as far, since the volume of fluid displaced is the same on both sides.

STUDY TIP

Before calculating, compare piston areas: the force ratio equals the area ratio, and the distance ratio is its inverse.

KEY POINTS

  • Force = Pressure × Area
  • Output force ratio equals output-to-input area ratio
  • Distance moved is reduced by the same ratio, so work is not gained

SOURCES

  • FAA-H-8083-30B ch05 "Pascal's Law"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.