The Reynolds Number

Inertia versus viscosity

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Reynolds number $Re = \rho v L / \mu$ compares inertia with viscosity.
• Low Re: smooth, laminar flow. High Re: turbulence.
• Swimmers live at Re ~ 10⁶; bacteria at Re ~ 10⁻⁵.

Steps

1. One number to rule them
2. A swimmer
3. Where turbulence begins
4. Dimpled golf balls
5. Water in a pipe
6. A bacterium