Navier Stokes Explained

Pour, stir and tilt a real fluid simulation, then watch each term of the Navier-Stokes equations push the water around. Four guided lessons, no sign-up.

The Navier-Stokes equations describe how every liquid and gas moves. They are usually met as a wall of symbols. Here they are a tank of water you can hold.

A real three-dimensional fluid solver runs on your iPhone's GPU. Drop a column of water, stir a tank, push a flow past a sphere, or turn on Tilt and let gravity follow your phone. Then look inside: color the water by speed, pressure or rotation, tap anywhere to measure it, and open the live values to see each term of the equation as an arrow at that point. In still water the pressure arrow and the gravity arrow cancel, which is what the equation says they must do.

FOUR GUIDED LESSONS Predict, watch, compare, explain. • Why does a swirl fade? The same stir in two liquids, 10,000 times apart in viscosity. • What holds water up? Measure pressure at two depths. • How does flow turn? A pulse of water meets a solid sphere. • Why doesn't water squash? The same falling column with pressure switched off.

A LAB, NOT A VIDEO • Gravity, viscosity and stirring strength are yours to change, with a live Reynolds number. • Velocity and pressure arrows, tracer trails, pause, single-step and half speed. • Every term of the equation opens a plain-language explanation and an experiment to try. • Works offline. No account.