# Heat capacity Heat capacity is how much [[Energy]] a substance needs to raise its temperature by one degree. Divide by mass and it is specific heat capacity; divide by moles and it is molar. It is the number that decides whether a material is a thermal buffer or a thermal lightweight — and [[Properties_of_water|water]]'s is extraordinarily high. ## Microsim — p5.js Sidecar: `Heat_capacity.p5.js` · route leaf: `microsim/p5js/Heat_capacity__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `power slider` | heat supplied per second | | `mass slider` | sample mass | | `[h]` | heater on / off | *What to watch:* Same heater, three substances. Watch the low-capacity one race ahead while water crawls — then stop heating and watch which one holds its temperature. ## Where the joules go Energy added to a substance distributes itself among every available way of moving: translation, rotation, vibration. A monatomic gas like [[Helium]] has only translation, so its molar heat capacity is small and its temperature rises fast. Add molecular structure and the same joules get shared more ways, so temperature rises less — which is [[Kinetic_theory_of_gases]] and the equipartition idea in one observation. This is also why heat capacity depends on whether volume or pressure is held constant: at constant pressure the substance also does expansion work, so it needs more, and the difference is exactly the pV term from [[Enthalpy]]. ## Thermal ballast Water's specific heat is roughly four times air's by mass and thousands of times by volume, which makes the ocean the planet's thermal flywheel and the reason coastal climates are mild. It is why [[Heat_transfer]] systems use water, why a [[WT!Energy_Center_of_Excellence|steam]] plant works, and why [[Thermocline|thermal stratification]] persists in a lake through a summer. Near absolute zero heat capacity itself collapses toward zero, which is the [[Third_law_of_thermodynamics]] showing up as a measurable curve. **Reads with:** *Thermodynamics and Chemistry, 2nd ed. (Howard DeVoe, 2020)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/thermodynamics-and-chemistry) · [download](https://www2.chem.umd.edu/thermobook/downloads.htm) · CC BY 4.0. Section 6 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Internal_energy]] · [[Enthalpy]] · [[Kinetic_theory_of_gases]] · [[Properties_of_water]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Heat_capacity) : [Wikitube](https://en.wikitube.io/wiki/Heat_capacity) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Physics]], [[PORTAL_Energy]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*