Liquids and gases differ in that:

States of matter properties: SOLID — fixed shape and volume; particles vibrate in place; strong intermolecular forces; nearly incompressible. LIQUID — fixed volume, no fixed shape (takes container shape); particles flow past each other; moderate intermolecular forces; nearly incompressible (compressible by only ~5% even under extreme pressure). GAS — no fixed shape OR volume; expands to fill any container; particles move freely with weak interactions; highly compressible (volume changes significantly with pressure). PLASMA — ionized gas, fourth state. Implications for ASVAB MC: (1) HYDRAULIC systems use liquids precisely BECAUSE they're incompressible — pressure transmits efficiently; (2) PNEUMATIC systems use compressed gas, providing spring-like behavior and energy storage; (3) Gas laws: pressure × volume = constant at constant temperature (Boyle's Law); volume increases with temperature (Charles' Law); pressure increases with temperature in fixed volume (Gay-Lussac's Law); combined: PV/T = constant. (4) Fluid (both liquid and gas) physics: pressure increases with depth (P = ρgh); buoyancy works in both; flow rate × area = constant (continuity equation); Bernoulli's principle relates pressure to velocity (faster flow = lower pressure — explains airplane lift, perfume atomizers, carburetors). Density: solids generally densest, liquids next, gases least dense; exceptions exist (mercury liquid denser than many solids; some solids less dense than liquid water like ice — which is why ice floats).