Shadows Cast by Spider Legs, Used in Physics Calculations

Anticipating Halloween, the American Chemical Society has published a study about using the shadows cast by (kinda sorta) spider legs, for scientific purposes. The paper is:

Elegant Shadow Making Tiny Force Visible for Water-Walking Arthropods and Updated Archimedes’ Principle,” Yelong Zheng, Hongyu Lu, Wei Yin, Dashuai Tao, Lichun Shi, and Yu Tian, Langmuir, 2016, 32 (41), pp. 10522–10528.  The authors, at Tsinghua University, China, report:


“Forces acted on legs of water-walking arthropods with weights in dynes are of great interest for entomologist, physicists, and engineers. While their floating mechanism has been recognized, the in vivo leg forces stationary have not yet been simultaneously achieved. In this study, their elegant bright-edged leg shadows are used to make the tiny forces visible and measurable based on the updated Archimedes’ principle. The force was approximately proportional to the shadow area with a resolution from nanonewton to piconewton/pixel. The sum of leg forces agreed well with the body weight measured with an accurate electronic balance, which verified updated Archimedes’ principle at the arthropod level”

(Thanks to Tony Tweedale for bringing this to our attention.)

BONUS: An earlier study that used shadow calculation: the MIT study “The hydrodynamics of water-walking arthropods“, by Ig Nobel Prize winner David Hu, and John Bush. Here’s a bit of detail from that study: