Brownian Motion and Einstein Diffusion Lab for A Level Physics

Observe Brownian motion, reveal the molecular model, compare temperature, viscosity and tracer size, then test Einstein's diffusion prediction with live mean-square-displacement data.

Learning guide and suggested activities

What this tool shows

The irregular motion of a visible particle suspended in a fluid
How unbalanced molecular collisions provide a kinetic-model explanation
The separate roles of temperature, viscosity and tracer radius in Brownian diffusion
How to save and compare two controlled sets of conditions
Why unpredictable individual motion produces predictable ensemble statistics
How mean-square displacement, diffusion coefficient and the Stokes–Einstein model are connected

OCR A relevance

OCR A H556 Module 5.1.2(c): Brownian motion and the kinetic model of matter
The smoke-particle demonstration and evidence for continual molecular motion
Thermal motion, absolute temperature and microscopic explanations

AQA relevance

AQA 7408 section 3.6.2.3: molecular kinetic theory model
Brownian motion as evidence for the existence of atoms
Temperature, molecular motion and thermal physics explanations

Try these tasks

Observe the tracer with the molecules hidden and write a description before selecting an explanation.
Reveal the molecular model and connect short-term collision imbalance with changes in tracer direction.
Change one of temperature, viscosity or tracer radius and use runs A and B to make a fair comparison.
Predict each change in diffusion coefficient from D = kBT/(6πηr), then test it in the simulation.
Release 64 tracers and use the gradient of the mean-square-displacement graph to estimate D.
Explain why random individual paths can still produce a predictable statistical relationship.