SortStack #3088 — 2034-11-22

By speed · Order from slowest to fastest.

1. The growth of a cave stalactite 0.1 mm/year

   Most stalactites lengthen by less than a tenth of a millimetre a year, dripping mineral by mineral over millennia.

2. The growth of human hair 175.3 mm/year

   Scalp hair grows roughly 1.25 centimetres a month, so a single strand reaching your shoulders is years old.

3. A crawling baby 1.4 km/h

   Babies often invent their own crawling styles, from the classic hands-and-knees to a one-legged commando shuffle.

4. A sea turtle cruising 3 km/h

   Sea turtles can hold their breath for hours while resting, slowing their heart to a beat every few minutes.

5. A racing greyhound 76 km/h

   Greyhounds reach their top speed in just a few strides and spend much of a sprint completely airborne.

6. A record tennis serve 270 km/h

   The fastest serves leave the racket so quickly the returner must react before the ball has even crossed the net.

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