• id: JME-08-N07
• title: Bulk Modulus and Compressibility
• tags: bulk-modulus, compressibility, pressure

Bulk modulus measures resistance to uniform compression: $B = \frac{-\Delta P}{\Delta V/V} = \frac{-\Delta P \cdot V}{\Delta V}$ The negative sign ensures $B > 0$ (volume decreases when pressure increases). SI unit: Pa. Unlike $Y$ and $G$, bulk modulus applies to all states of matter — solids, liquids, and gases. Compressibility is the reciprocal: $k = 1/B$ (Pa$^{-1}$). For an ideal gas: at constant temperature, $B_{\text{isothermal}} = P$; at constant entropy, $B_{\text{adiabatic}} = \gamma P$.