Physicists Find That Animals’ Top Speeds Are Proportional to Body Length

Despite the wide variety of shapes and sizes in the animal kingdom, some things remain constant across almost all species, small or large. For instance, an elephant pees for approximately the same amount of time as a house cat, though the former has a bladder 3600 times larger. A similar effect, it seems, governs the top speed of an animal’s run. Though a bacterium is considerably smaller than an elephant, they both move at the same maximum speed relative to their body length, according to a new paper in the American Journal of Physics.

Two Parisian scientists argue that almost all animals, with the exception of those that fly, have an approximate top speed of about ten times their body length per second. According to their calculations, the animal’s mass doesn’t matter. In their analysis, the premise holds true for organisms as small as bacteria and as big as whales—a size difference of about 21 orders of magnitude.

An animal’s maximum velocity has little to do with its body mass. Image Credit: Meyer-Vernet et al., American Journal of Physics (2015)

The paper is theoretical, not experimental, so it’s more of a rough approximation that may miss some of the nuances of variation between individuals and species. For a more in-depth explanation of the science involved, see this article from Physics Forum Insights.

[h/t: Kottke]