Adrian Bejan | Nature's wheel and bicycle, from Design in Nature

Aug 21, 2025

The video develops the idea that movement in animals and humans follows a natural design that can be understood as a kind of wheel, showing how steps, strides, and rhythms are tied to physical form, balance, and efficiency. By looking at how walking, running, and swimming are shaped by size, strength, and body mechanics, the discussion connects the natural wheel of life to the history of human technology, including the wheel and the bicycle. It highlights how lighter and more efficient designs appear both in nature and in human invention, showing that movement always tends toward reducing wasted effort and increasing adaptability. In this way, the video links the laws of design in nature with human practices, drawing attention to the deep connection between biology, physics, and technology.

When describing the movement of humans and animals, the explanation shows that what appears to be straight walking is a falling and catching cycle, where each step prevents collapse. The body’s center of mass constantly leans forward and is restored by the action of the legs, making walking essentially a rhythm of controlled falling. This rhythmic pattern highlights why balance is delicate and why walking can be compared to an inverted pendulum, prone to instability yet sustained by repetition.
The size of the body strongly influences performance, as seen in both running and swimming. Taller athletes gain advantages because their movements lift their mass higher and project them forward with greater efficiency, making body length a predictor of speed. The same principle explains why sprinters begin races leaning forward, using rapid steps to prevent falling, and then transition to a vertical position as they stabilize their rhythm. The video shows that these mechanical patterns apply across different forms of movement and environments.
By comparing walking with the rotation of a cylinder or sphere, the explanation visualizes human gait as a wheel-like cycle. When the motion is traced step by step, it becomes clear that bipedal walking is equivalent to a wheel with two spokes, one leg replacing the other. This comparison reveals that nature already created the wheel before human technology, using legs as rotating supports that achieve rolling motion without a man-made axle.
The discussion of wheels in human history shows that technology gradually followed nature’s path toward lighter structures. Ancient solid wheels evolved into spoked designs, which became thinner and more numerous during the medieval period, and finally into aerodynamic versions with very few spokes for racing bicycles. The movement toward lighter wheels mirrors the principle found in nature, where legs bend and adapt to uneven terrain more effectively than rigid wheels ever could.
Extending the idea further, quadrupedal animals are shown to operate like four-spoked wheels, each leg forming part of a rolling cycle. The advantage of natural wheels lies in their flexibility: knees and joints allow rolling over irregular surfaces with stability, something technological wheels struggle to achieve. Even advanced vehicles built for uneven terrains cannot match the adaptability of living bodies, reminding us that natural design often outpaces human invention in efficiency and elegance.

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