Speedy sharks and golf balls
First posted on homepage: 5 December 2011 (GMT+10)
Re-posted on homepage: 27 October 2021 (GMT+10)
Shark species that can hurtle through the ocean at high speed—up to 80 km per hour (50 mph)1 —have a number of special features that allow them to do that, e.g., the tiny scales on the surface of their skin.
Each scale is just 0.2 mm (0.008 inch) long and is made of tough enamel—if you touch shark skin it feels like rough sandpaper. You might at first think that a perfectly smooth surface would be better for speed but in fact it’s been known for some time that the scales actually reduce drag.2 And now researchers have discovered another special characteristic of shark skin. In light of evidence that some shark species may bristle their scales during fast swimming, engineers decided to see how lifting the scales on end affects water flow over the shark.
Using models of bristled shark skin in a water tunnel experiment, researchers from the University of Alabama’s Aerospace Engineering and Mechanics Department and their colleagues observed that at high speed, tiny vortices or whirlpools formed within the cavities between the scales.3 (The scales were raised at an angle of 90º to the surface of the skin.) The effect of these vortices was to form a kind of ‘buffer layer’ between the fast moving fluid and the skin’s surface, thus preventing a turbulent wake from forming behind the shark. In other words, reducing drag.
‘It’s like the difference between pushing a box over ball bearings instead of dragging it along the floor,’ said lead researcher Amy Lang.4 She explained that the same principle applies to the dimples on golf balls. As a well-struck golf ball hurtles through the air, its dimples create mini vortices which reduce drag, just as the cavities formed on the surface of shark skin do when the scales are stood on end.
Just as golf balls with dimples are intentionally designed that way5 (having less drag than if made perfectly smooth, a dimpled golf ball travels further),6 so too ‘dimpled’ shark skin did not come about by accident, but by design. The Bible speaks of that Designer—the Creator of the heavens and the earth, the seas and all that is in them7 (including sharks)—and scientists are still discovering just how good His designs really are.8,9
- E.g. the shortfin mako shark. Return to text.
- Similarly, researchers have discovered that the large bumps of a humpback whale’s flipper reduce drag by an incredible 32%. See Sarfati, J., Flighty flippers, Creation 27(2):56, 2005. And in dragonflies, too, the highly corrugated wings have been found to outperform similarly sized streamlined wings. See: Low drag on dragonflies, Creation 31(1):10, 2008. Return to text.
- Lang, A., Motta, P., Hidalgo, P. and Westcott, M., Bristled shark skin: a microgreometry for boundary layer control?, Bioinspiration and Biomimetics 3(4): doi 10.1088/1748-3182/3/4/046005, December 2008. Return to text.
- Robson, D., Why a speeding shark is like a golf ball, New Scientist, www.newscientist.com/article/dn15151-why-a-speeding-shark-is-like-a-golf-ball.html, 7 November 2008. Return to text.
- The early golf balls, in the 1800s, were designed to have a smooth surface, since people believed a smooth sphere would result in less drag and thus fly further. It was later discovered that the ball flew further if the surface was scored or marked. By 1930, the current golf ball with its dimpled enamel coat was accepted as the standard design. Cislunar Aerospace, Aerodynamics in Sports Equipment, Recreation and Machines—Why does a golf ball have dimples?, wings.avkids.com/Book/Sports/instructor/golf-01.html, 17 November 2008. Return to text.
- University of Illinois at Urbana-Champaign—Physics Van Outreach Program, Dimples on a golf ball, van.physics.uiuc.edu/qa/listing.php?id=945, 19 July 2006. Return to text.
- See, e.g., Exodus 20:11.Return to text.
- The research team hope further investigations will lead to design of better torpedoes and underwater vehicles inspired by shark skin that can move more quickly through water and change direction more easily. Return to text.
- For more examples of God’s awesome designs, see Dr Jonathan Sarfati’s book By Design, available addresses p. 2. Return to text.