# Drag (physics) > [[PORTAL_Dynamical_system|Dynamical system]] spine. ## Microsims — three.js <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/drag_(physics)_microsim.html" width="100%" height="520" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" title="Drag (physics) — three.js microsim"></iframe> </div> <p class="wt-pending"><strong>Note:</strong> staged, awaiting CDN deploy.</p> Drag is the force that opposes an object's motion through a fluid — air or water, most commonly — acting parallel to the flow and directly opposite the direction of travel. It arises from friction between the object's surface and the fluid, and from the pressure difference the object creates as it pushes fluid out of its path. ## Overview This build renders an object moving through a fluid medium with drag force live-computed and visualised as it responds to changing speed, size, and shape, letting the standard drag equation's dependence on velocity squared be seen directly rather than read as a formula. Drag is one of the clearest everyday examples of a dissipative force in a [[Dynamical_system|dynamical system]]: unlike gravity or an ideal spring, it constantly removes energy from motion, which is why a dropped object reaches a stable terminal velocity instead of accelerating forever, and why most real-world trajectories settle toward simpler long-term behaviour than their frictionless equations would predict. **On the spine:** [[Dynamical_system]] · [[Physics]] · [[Complex_system]]. <!-- SPINEPATH:BEGIN g20 — shortest chain of Wikipedia links between local articles to a Compendium Main article; do not hand-edit inside --> *Connected to the Apex Spine:* Drag (physics) → [[Fluid_dynamics|Fluid dynamics]] — [[WT!Thury_Hydrodynamics_Compendium|Compendium]] section 1, *Fluid dynamics*. <!-- SPINEPATH:END --> <!-- COMPENDIUMLINK:BEGIN g19 — generated from _registry/plans/THURY_COMPENDIUM_SECTIONS.md; do not hand-edit inside --> *Linked from the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]], section 23, Boundary layers and drag.* <!-- COMPENDIUMLINK:END --> <!-- THURYSIM:BEGIN g21 — Thury Compendium microsim (framework build, specs/variants/Drag_(physics).json); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Drag (physics)* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Drag_(physics).html" data-title="Drag (physics)"></div> *Built from `MICROSIM_GUIDE/specs/variants/Drag_(physics).json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.* <!-- THURYSIM:END --> ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Drag_(physics)) : [Wikitube](https://en.wikitube.io/wiki/Drag_(physics)) --- *Repopulated 2026-08-05 · existing three.js asset renamed + wired, Wikipedia-sourced overview · 0 deletions.*