# Drinking and Diving

GFSW01 - Form and deformation in solid and fluid mechanics

I will discuss two fluid-mechanics problems exploited by biological systems.

First, animals that drink must transport water into the mouth using either a pressure-driven (suction) or inertia-driven (lapping) mechanism. Previous work on cats shows that these mammals lap using a fast motion of the tongue with relatively small acceleration (1g), in which gravity is balanced with steady inertia in the liquid. Do dogs employ the same physical mechanism to lap? To answer this question, we recorded 19 dogs while lapping and conducted physical modeling of the tongue's ejection mechanism. In contrast to cats, dogs accelerate the tongue upward quickly (1-4g) to pinch off the liquid column. The amount of liquid extracted from the column depends on whether the dog closes the jaw before or after the pinch-off. Our recordings show that dogs close the jaw at the moment of pinch-off time, enabling them to maximize volume per lap.

Second, several seabirds (e.g. Gannets and Boobies) dive into water at up to 24 m/s as a hunting mechanism. We studied how diving birds survive water impacts because of their beak shape, neck muscles even with a long slender neck. The birds’ slender necks appear fragile but do not crumble under the compression due to high-speed impact. First of all, we use a salvaged bird to resolve plunge-diving phases and the skull and neck anatomical features to generate a 3D-printed skull and to quantify the effect of the neck’s musculature to provide the necessary stability. Then, physical experiments of an elastic beam as a model for the neck attached to a skull-like cone revealed the limits for the stability of the neck during the bird’s dive as a function of impact velocity and geometric factors. We find that the small angle of the bird's beak and the muscles in the neck predominantly reduce the likelihood of injury during a high-speed plunge-dive. Finally, we di scuss maximum diving speeds for humans using our results to elucidate injury avoidance.

This talk is part of the Isaac Newton Institute Seminar Series series.