Adrian Bejan | Serpentines, Galilei, & the fish, from Design in Nature
In this video, Adrian Bejan begins with the familiar model of animal motion, where effort is split into two parts: vertical and horizontal. He revisits the freedom to change as a way for animals to minimize total effort, linking movement to hunger, food search, and the environments that shape behavior. Bejan introduces R as the resistance factor that differentiates movement in air, water, and on land. He then presents a new challenge, the observation that fish do not seem to fight gravity the same way flyers and runners do. Along the way, Bejan dives into history, revisiting Galilei and his experimental proof of acceleration, not through high technology, but with wet boards and dripping water.
Bejan discusses how animals balance W1 (vertical effort) and W2 (horizontal effort), emphasizing that the trade-off determines optimal speed and rhythm.
He explains how R varies across media, lowest in air, highest in water, intermediate on land, and how terrain complexity affects movement, making serpentine paths preferable on steep or bushy landscapes.
Bejan draws parallels between optimal animal speed and free-fall velocity, showing how larger animals reach greater speeds due to body mass and density.
He introduces Galilei’s method of observing acceleration using dripping water and wooden boards, highlighting early experimental design and the scientific method.
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Umit Gunes, Ph.D.
Assoc. Prof. | Yildiz Technical University
Editor | International Communications in Heat and Mass Transfer
Guest Editor | Philosophical Transactions of the Royal Society A
Guest Editor | BioSystems
Web | umitgunes.com