Note: Please email Mini Thomas, [email protected], for meeting password.

Fluids are vital to all life forms, and organisms have presumably adapted their behaviors or features in response to mechanical forces on the body to achieve better performance. In this talk, I will discuss two biological problems in which animals exploit mechanics principles. First, we investigated how animals transport water into the mouth using an inertia-driven (lapping) mechanism. Dogs accelerate the tongue upward (up to 4 g) to create a larger water column while drinking, whereas cats use a tongue motion with relatively small acceleration. We found that to maximize water intake per lap, both cats and dogs close the jaw at the column break-up time governed by unsteady inertia. This break-up (or pinch-off) time can be predicted using the stability analysis of the water column in which surface tension balances with inertia. Second, we studied how birds with long slender necks plunge-dive and survive from the impact. Physical experiments using an elastic beam as a model for the neck attached to a skull-like cone revealed limits for the stability of the neck during plunge-dive. This neck response can be simplified as the Euler beam buckling problem with unsteady impact force on the head. We found that the small angle of the bird’s beak and the strong muscles of the neck predominantly reduce the likelihood of injury during high-speed plunge dives. If time permits, I will discuss the mechanism of head acceleration to release water lodged in the ear canal, which is analogous to the Rayleigh-Taylor instability.