Glossary
hydraulics
Hydraulics uses a liquid under pressure to transmit force. Because liquids barely compress, a small push on a small piston produces a much larger force on a big one.
Hydraulics is the use of a liquid under pressure to transmit force. Because liquids are almost incompressible, pushing a liquid inside a closed system passes the push along to wherever the liquid reaches, which is how one brake pedal stops four wheels and a small jack lifts an entire car.
The multiplying effect is Pascal's principle: pressure applied anywhere in a confined liquid is transmitted equally throughout it, and force is pressure times area. Push a small piston into the fluid and the same pressure acts on a much larger piston, giving a larger force — your effort moves a long way and the load moves a short way.
That exchange is why hydraulic brakes are so light to press and why a hydraulic jack lifts so much: a small force over a large travel becomes a large force over a small travel. The catch is that the system must be sealed and free of air, since a gas can be squeezed and would blunt the push.
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Related terms
- density — Density is how much mass is packed into a given volume — mass divided by volume. An object floats in water when its density is lower than water's and sinks when it is higher.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)