Science
What is Brownian motion?
Brownian motion is the random, jittery movement of tiny particles suspended in a fluid, caused by countless molecules of that fluid colliding with them. It is visible proof that matter is made of fast-moving, invisible atoms and molecules.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains brownian motion.
Key things to understand
- 1Pollen grains or dust specks in water jiggle erratically with no outside push.
- 2The cause is constant, uneven bombardment by the fluid's moving molecules.
- 3Einstein explained it mathematically in 1905, giving strong evidence atoms are real.
- 4The smaller the particle, the more visible the jiggling.
- 5It's an everyday example of statistical, random ('stochastic') motion.
Frequently asked questions
- What causes Brownian motion?
- Invisible fluid molecules in constant motion strike the particle from all sides; the imbalance of these hits at any instant nudges it randomly.
- Why is Brownian motion important?
- Einstein's 1905 analysis of it gave some of the first hard evidence that atoms and molecules actually exist.
- Where do you see Brownian motion?
- Dust dancing in a sunbeam, ink spreading in still water, and smoke particles drifting all show it.