Body Shape Reduces Friction

a pacific bottlenose dolphin swims in blue ocean water from above

Biological Strategy

Bottlenose dolphin

AskNature Team

Image: Jen Milius / Unsplash / Free non-commercial use

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Manage Turbulence

A turbulent force occurs when air or water creates a chaotic or irregular motion. The source can be such things as wind, waves, and eddies caused by obstructions to air or water flow (such as that created by a rock in a stream). Because the force is irregular, it acts in unpredictable ways on multiple parts of a living system at any given time, decreasing the living system’s efficiency. Strategies used to manage turbulence include dampening the amount of turbulence, having flexibility to handle sudden changes, and making quick adjustments. An example is the mucus on aquatic organisms, such as barracuda sharks, that can reduce turbulent friction of seawater by 66%. In doing so, it decreases drag and increases the sharks’ swimming efficiency.

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Move in/on Liquids

Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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The body of the dolphin has low friction in water by having an optimal length to diameter ratio.

Image: Frank Wirth Whales-dolphins / Wikimedia Commons /

Bottlenose Dolphin (''Tursiops truncatus'') Junping

Image: NASA / Wikimedia Commons /

“The streamlined body of optimal shape has a length of 4.5 times its diameter. In this case the surface is smallest relative to the volume. This optimal numerical proportion has not remained a secret from nature: for dolphins (Tursiops gilli) the ratio is close to 5.” The author goes on to talk about the Reynolds number and how the shape of the dolphin shows high efficiency: “As a matter of fact, the maximal diameter of the dolphin is slightly back of center. Obviously, the above-mentioned effect was taken into consideration. Experiments have confirmed that this particular shape lowers friction drag in turbulent boundary layers to 65%.” (Tributsch 1983: 48)

Last Updated October 14, 2016

References

Book

How Life Learned to Live: Adaptation in Nature

01/01/1983 | Helmut Tributsch

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Reference

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