In a breakthrough study conducted at Kyoto University, a team of fluid dynamics and mathematical modelers led by Kenta Ishimoto, Clément Moreau, and Kento Yasuda has unraveled the mystery behind how sperm and other minuscule organisms manage to bypass Newton’s third law of motion. Published in the prestigious journal PRX Life, their research sheds light on how certain creatures can effortlessly navigate through viscous fluids, ultimately enabling them to conserve energy and survive with minimal food consumption.
As physics students learn, Newton’s third law of motion asserts that every action is met with an equal and opposite reaction. This principle can be observed in experiments involving objects colliding, such as marbles. However, in the realm of natural phenomena, certain organisms have evolved ingenious adaptations that allow them to circumvent this law—a peculiarity that has intrigued scientists for decades.
Driven by curiosity, the researchers set out to examine the movement of algae and sperm cells in order to uncover the secrets of their seemingly effortless locomotion through fluids. Conventionally, swimming through viscous liquids requires exerting considerable effort. To understand how these diminutive cells defy expectations, the team employed cutting-edge microscopy techniques to closely observe their movements.
Under the microscope’s watchful eye, the researchers discovered a captivating similarity between Chlamydomonas algae and human sperm cells—they both employ flagella to propel themselves forward. These hairlike appendages generate wave-like motions, resulting in a push-and-pull mechanism that enables the cells to traverse their liquid environments. However, based on Newton’s third law, these actions should generate substantial resistance from the fluid, thus impeding progress. Surprisingly, this was not the case.
Upon careful examination, the scientists unearthed a fascinating phenomenon that explained the cells’ remarkable efficiency. Although the sperm cells appeared to execute the expected flagella movements, the team noticed an additional factor at play. The flagella exhibited a unique “odd elasticity,” allowing them to bend and respond to the fluid’s resistance in minute ways. This responsiveness, often likened to a dance with the viscous medium, enabled the flagella to circumvent an equal and opposite reaction—an ingenious mechanism that conserved the cells’ energy.
Unlocking the secrets of efficient movement in microscopic organisms has far-reaching implications. By understanding how these creatures navigate through dense fluids while conserving energy, scientists can extrapolate this knowledge to various fields. For instance, it could inspire the development of innovative propulsion systems, such as bio-inspired robots that can maneuver through complex environments and conserve energy.
Through their pioneering research, Ishimoto, Moreau, and Yasuda have demystified the enigmatic movement of sperm and algae. By examining the behavior of flagella on these tiny organisms, they have revealed how their unique elasticity allows them to sidestep the anticipated resistance from fluids, conserving energy in the process. This groundbreaking study in fluid dynamics opens new doors for scientific exploration and advances our understanding of the complex mechanisms that underlie efficient movement in the natural world.
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