Washington, June 14 (IANS) A mechanical engineer argues that just as the design of the wheel became lighter with fewer spokes over time, and better at distributing the stresses of hitting the ground, animals too have evolved to move better on Earth.
In essence, over millions of years, animals such as humans developed the fewest ‘spokes,’ or legs, as the most efficient method for carrying an increasing body weight and height more easily.
‘This prediction of how wheels should emerge in time is confirmed by the evolution of the wheel technology,’ said Adrian Bejan, professor of mechanical engineering at Duke University’s Pratt School of Engineering.
‘For example, during the development of the carriage, solid disks were slowly replaced by wheels with tens of spokes.’
The advantage of spokes is that they distribute stresses uniformly while being lighter and stronger than a solid wheel.
‘In contrast with the spoke, the solid wheel of antiquity was stressed unevenly, with a high concentration of stresses near the contact with the ground, and zero stresses on the upper side,’ Bejan said.
‘The wheel was large and heavy, and most of its volume did not support the load that the vehicle posed on the axle.
‘If you view animal movement as a ‘rolling’ body, the two legs, swinging back and forth, perform the same function of an entire wheel-rim assembly,’ Bejan said.
‘They also do it most efficiently – like one wheel with two spokes with the stresses flowing unobstructed and uniformly through each spoke. The animal body is both wheel and vehicle for horizontal movement.’
‘An animal leg is shaped like a column because it facilitates the flow of stresses between two points – like the foot and hip joint, or paw and shoulder,’ Bejan said. ‘In the example of the Neolithic stone wheel, the flow of stresses is between the ground and the whole wheel.’
Bejan believes that the constructal theory of design in nature, which he started describing in 1996, predicts these changes in the wheel and animal movement.
The theory states that for a design (an animal, a river basin) to persist in time, it must evolve to move more freely through its environment.
Since animal locomotion is basically a falling-forward process, Bejan argues that an increase in height predicts an increase in speed.
For a centipede, each leg represents a point of contact with ground, which limits the upward movement of the animal. As animals have fewer contacts with ground, they can rise higher with each stride.
An earlier analysis by Bejan showed that larger human swimmers are faster because the wave they create while swimming is larger and thus carries them forward faster, says a Duke release.
While wheel-like movement evolved naturally, it also describes what Bejan likes to call ‘nature’s gear box.’ Humans have two basic speeds, Bejan said – walking and running. A running human gets taller, or higher off the ground, with each stride, which increases his speed.
Bejan’s analysis was published in the American Journal of Physics.
