Lesson Plan

• Describe Brownian motion as the random jitter of particles suspended in a fluid.
• Explain how continuous molecular bombardment produces this motion.
• Analyse how temperature and particle size affect the intensity of Brownian motion.
• Apply the Stokes‑Einstein relation to estimate a diffusion coefficient (optional).
• Identify and correct common misconceptions about Brownian motion.

• Projector or interactive whiteboard
• Microscopy video or live demonstration of particles in fluid
• Printed worksheet with key points and questions
• Calculator (for quantitative part)
• Whiteboard and markers
• Handout of a diagram showing random molecular impacts

Show a short video of microscopic particles jittering in water to spark curiosity about why they move. Review the particle model and kinetic theory covered in previous lessons. State that by the end of the lesson students will be able to describe and explain Brownian motion and link it to molecular collisions.

1. Do‑now (5'): Answer a quick question on kinetic theory and molecular motion.
2. Video demonstration & class discussion (10'): Observe Brownian motion and brainstorm possible causes.
3. Teacher explanation (12'): Detail random molecular bombardment and relate it to the observed jitter.
4. Group worksheet activity (10'): Investigate how temperature and particle size influence motion intensity.
5. Optional quantitative exercise (8'): Use the Stokes‑Einstein equation to calculate a diffusion coefficient.
6. Misconception check & short quiz (5'): Address common errors and assess understanding.

Recap that Brownian motion provides observable evidence for molecules and varies with temperature and particle size. Have each student write an exit‑ticket sentence explaining the cause of the motion. Assign homework to research another real‑world example of Brownian motion and prepare a brief description for the next class.