Life at Low Reynolds Number
| Author | E. M. Purcell |
|---|---|
| Published | 1977 |
| Format | Talk |
| Original | Read the original |
TL;DR — Physicist E. M. Purcell’s famous talk on how bacteria swim in a world where viscosity dominates and inertia is irrelevant, so ordinary swimming strokes get nowhere.
Published in the American Journal of Physics 45 (1977), a lightly edited transcript of a talk the Nobel physicist Edward Purcell gave at a 1976 symposium honouring Victor Weisskopf. The editor’s note says the talk’s personal tone was kept and the figures reproduce his overhead transparencies; the live demonstration used a tank of corn syrup.
Purcell explains that for microorganisms the Reynolds number is around 10⁻⁴, so viscous forces swamp inertia: a bacterium that stops swimming stops almost instantly. He shows why a reciprocal motion, like a scallop opening and closing, produces no net movement (the “scallop theorem”), how corkscrew flagella get around this, and why diffusion means a bacterium gains nothing by swimming toward food it could simply wait for.
What it is: a classic, much-taught physics essay. The linked copy is hosted on a University of Cambridge (DAMTP) faculty page, not by the publisher.
Where this came from
- A copy saved in October 2026.
- Original source: https://www.damtp.cam.ac.uk/user/gold/pdfs/purcell.pdf
9 pages. A copy is archived locally against link rot; the header links the original source.