Activity

Brownian motion - watching molecule movement

Summary
Using a transmission microscope, watch molecules bump into tiny fat droplets in milk, to observe the motion of molecules.
Science content
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Physical Changes, Solutions, Mixtures and Separating (2, 4, 5, 6)
Materials
  • transmission microscope to view at 100X and 400X
  • slides and coverslips
  • 2% milk
Procedure

Make a slide with a drop of 2% milk, and place under the microscope.
Wait until the milk has stopped streaming around the slide, and the individiual fat droplets in the milk stay within the field of view.
Look closely for the fat droplets jiggling around - caused by water molecules bumping into them!
Brownian motion was the first convincing evidence that atoms and molecules existed.

Grades taught
Gr 5
Teaching site
Dorothy Lynas Elementary
ingridscience afterschool