The stereotypical reaching motion of the octopus arm has drawn growing attention for its efficient control of a highly deformable body. Previous studies suggest that its characteristic bend propagation may share underlying principles with the dynamics of a whip. This work investigates whether whip-like passive dynamics in water can reproduce the kinematic features observed in biological reaching and their similarities and differences. Platform-based whipping tests were performed in water and air while systematically varying material stiffness and driving speed. Image-based quantification revealed that the Ecoflex Gel 2 arm driven at 150 rpm (motor speed) reproduced curvature propagation similar to that observed in octopus reaching. However, its bend-point velocity decreased monotonically rather than exhibiting the biological bell-shaped profile, confirming that the octopus reaching movement is not merely a passive whipping behavior. The absence of propagation in air further highlights the critical role of the surrounding medium in forming octopus-like reaching motion. This study provides a new perspective for understand biological reaching movement, and offers a potential platform for future hydrodynamic research.

翻译：章鱼腕足的典型伸展运动因其对高度可变形体的高效控制而日益受到关注。先前研究表明，其特有的弯曲传播可能与鞭子的动力学原理存在共通之处。本研究探讨了水中鞭状被动动力学是否能重现生物伸展中观察到的运动学特征，并分析其异同。我们在水中和空气中进行了基于平台的鞭打测试，并系统性地改变材料刚度和驱动速度。基于图像的量化分析表明，以150 rpm（电机转速）驱动的Ecoflex Gel 2臂状结构重现了与章鱼伸展相似的曲率传播现象。然而，其弯曲点速度呈单调递减趋势，而非生物运动中观察到的钟形分布，这证实了章鱼伸展运动并非单纯的被动鞭打行为。空气中传播现象的缺失进一步凸显了周围介质在形成类章鱼伸展运动中的关键作用。本研究为理解生物伸展运动提供了新视角，并为未来流体动力学研究提供了潜在平台。