Class practical: Marbles in a tray illustrate the meaning of 'mean-free-path'.

Practical Activity 14-16

Demonstration: A difficult exercise, photographing marbles to show the differences in their path lengths between collisions.

Practical Activity 14-16

Class practical: Finding displacement after ‘random walk’ using triangular-grid graph paper.

Practical Activity 14-16

Class practical: Finding displacement after ‘random walk’ using squared paper.

Practical Activity 14-16

√N steps gives the average mean free path for a bromine molecule in its wandering amongst air molecules. That would be similar...

Teaching Guidance 14-16

It is interesting for students to see how far physicists can push ‘back of the envelope’ calculations. Diffusing bromine into...

Teaching Guidance 14-16

This proof of R = s√N describes an algebraic approach to the random walk problem, sometimes known as the drunkard’s walk: If...

Teaching Guidance 14-16

Once students understand the thinking behind estimates of mean free path, s , they can estimate the time for air molecules to...

Teaching Guidance 14-16