Glossary
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.
Density is how much mass is packed into a given volume: mass divided by volume. A block of lead and a block of aluminum of the same size have very different densities, which is why the lead one is far heavier to lift.
The usual units are grams per cubic centimeter, and water is the benchmark at about 1. An object floats in water when its density is lower than water's and sinks when it is higher — a steel bolt sinks, an ice cube floats — and it is that comparison, not weight on its own, that decides. Changing the size of an object does not change its density, because the mass and the volume both change together.
Density questions usually hand you two of the three numbers and ask for the third, so the algebra is worth holding: density is mass over volume, mass is density times volume, and volume is mass over density.
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Related terms
- 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.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)