The Wet-Dog Shake

TL;DR

This study investigates how wet animals rapidly oscillate their bodies to shed water, using high-speed imaging and physics analysis to understand the mechanics behind self-drying through body shake.

Contribution

It combines experimental imaging and force analysis to elucidate the physical principles enabling animals to dry themselves efficiently by shaking.

Findings

Identifies the oscillation frequencies needed for effective water drop ejection.

Demonstrates the relationship between animal size and drying frequency.

Provides a physics-based model for the self-drying process.

Abstract

The drying of wet fur is a critical to mammalian heat regulation. In this fluid dynamics video, we show a sequence of films demonstrating how hirsute animals to rapidly oscillate their bodies to shed water droplets, nature's analogy to the spin cycle of a washing machine. High-speed videography and fur-particle tracking is employed to determine the angular position of the animal's shoulder skin as a function of time. X-ray cinematography is used to track the motion of the skeleton. We determine conditions for drop ejection by considering the balance of surface tension and centripetal forces on drops adhering to the animal. Particular attention is paid to rationalizing the relationship between animal size and oscillation frequency required to self-dry.