Brownian Motion

Jiggling pollen and diffusion

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Brownian motion is a random walk driven by molecular collisions.
• Distance $\propto \sqrt t$, so time $\propto$ distance².
• Diffusion is fast at the scale of cells and slow at the scale of bodies.

Steps

1. Proof of atoms
2. Jostled by molecules
3. A spreading cloud
4. Diffusion time
5. Einstein’s formula
6. Diffusing a metre
7. Inside a cell