费曼错了吗?——意大利面折断实验再研究

WAS FEYNMAN WRONG? — RESTURY OF THE SPAGHETTI BREAK EXPERIMENT

  • 摘要: 意大利面是人们日常的美食,美味又劲道。当我们用双手分别捏住干意面的两端并向中间用力弯折时,意面通常会断裂为3段、4段、5段甚至更多段,而很少断成两段。为了搞清楚为什么意面总是断成好几段,而不只是两段,诺贝尔物理学奖获得者、美国物理学家理查德·费曼曾经花一晚上时间在厨房掰干意面来研究,也没有给出合理的解释。干意面的断裂过程是在瞬间完成的,只有0.2~0.5 ms,断裂过程很难用肉眼看清并进行定量分析。本文设计了一款折断干意面的装置,并在高速相机的帮助下,研究干意面在不同给定参数下断裂的统计行为,并捕捉其断裂的细节过程。干意面的多节断裂并不是同时发生的,而是先在一个点处断裂,导致曲率的突变,由此激发了振动波,振动波可以增加意面局部的曲率,当某个地方的曲率达到一定的界值后进而产生多次断裂。同时,干意面断裂的段数和弯折的速度有关。 更有意思的是,折断过程中频繁出现断成两段的情形,这与费曼以及其他人的观察不相同,也给费曼提供了折断成两节的新方法。

     

    Abstract: Spaghetti is a staple delight, both delicious and robust. When we grasp each end of a dry spaghetti strand and forcefully bend it towards the center, it typically shatters into three, four, five, or more pieces, but seldom just two. Intrigued by why spaghetti often breaks into several fragments rather than two, Nobel Prize-winning physicist Richard Feynman famously spent an evening in his kitchen breaking spaghetti strands, yet he couldn't provide a satisfactory explanation. The fracture process of dry spaghetti happens in a mere instant, under 30 milliseconds, making it challenging to observe with the naked eye or analyze quantitatively.In this paper, we present a device specifically designed to break dry spaghetti, utilizing a high-speed camera to explore the statistical behavior of spaghetti fracture under various parameters. We capture the intricate details of the fracturing process. Interestingly, the fractures in dry spaghetti do not occur simultaneously. Initially, a fracture at a single point causes a sudden change in curvature, triggering a vibrational wave that increases local curvature elsewhere along the strand. When the curvature at any point reaches a certain threshold, fractures occur at multiple points. Moreover, the number of segments into which the spaghetti breaks correlates with the bending speed. Notably, our observations reveal that spaghetti frequently breaks into two pieces, contradicting Feynman's and other previous observations.

     

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