SortStack #3235 — 2035-04-18

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. A bottlenose dolphin 60 km/h

   Dolphins sleep with half their brain at a time, keeping one eye open to breathe and watch for danger.

3. A running reindeer 80 km/h

   Reindeer eyes change colour with the seasons, turning blue in winter to see better in the dim Arctic light.

4. 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.

5. A bullet train at full speed 330 km/h

   Japan's bullet trains have a near-perfect safety record, with average delays measured in seconds, not minutes.

6. NASA's X-43 scramjet 11.9K km/h

   The X-43 set an air-breathing speed record by burning fuel in a stream of air rushing through it many times faster than sound.

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