Stokes’ Law & Settling

Why clouds float

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

• Stokes' law: drag $= 6\pi\mu r v$ at low Reynolds number.
• Terminal speed $\propto r^2$, so tiny droplets fall extremely slowly.
• Cloud droplets float because they fall at only about 1 cm/s.

Steps

1. Drag on a tiny sphere
2. Falling droplets
3. Twice the size
4. Fog
5. A speck of dust
6. Volcanic ash