Speed Explainer:How Fast things work
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Size MattersWhat's faster--a falcon or a moth?
Posted Friday, Dec. 5, 2008
Speed is relative: it is important to account not just for absolute speeds, but also speeds in relations to sizes. In that light, what's faster: a cheetah or a falcon? Or, for that matter, an insect?
The peregrine falcon blows the cheetah away in terms of both absolute speed and speed relative to body size. The cheetah is generally thought to max out at around 75 miles per hour, while the peregrine falcon, in its dive--known as its "stoop"--has been clocked at 244 mph. Given that even smaller cheetahs tend to be longer than the largest peregrines' wingspans, which can reach over 45 inches, the bird of prey wins this one.
But some of the fastest insects, such as the sphinx moth, have been known to fly at a speed of over 30 mph, while the sphinx moth's wingspan is approximately three inches. So where the peregrine flies about eight times as fast as the sphinx moth, its wingspan is anywhere from ten to fifteen times as long. Advantage: the sphinx moth.
Even non-flying insects can be extremely fast for their sizes. At Purdue University's annual "Bug Bowl," American roaches race at speeds upwards of 3.5 mph. If racehorses raced at a speed in the same proportion to their body size, they would fly around the track at approximately 200 mph.
Bonus Explainer: Roach-whispering. Whispering into your roach's ear right before a race can actually speed it up, because--whether or not it can understand you--your speech will heat the bug up, enabling it to go faster.
Explainer thanks Professor Tom Turpin of Purdue University.
