Meeting Abstract

S10.2-5  Tuesday, Jan. 7 11:34  To eject a drop, from wet-dog shaking to urination HU, David*; DICKERSON, Andrew; YANG, Patricia; Georgia Institute of Technology

Animals frequently expel fluids from both their surfaces and inside their bodies. Undesired fluids include include rain and dew, accumulated on their surfaces, as well as the products of metabolism from within their bladder. As animals decrease in size, the specific forces required becomes larger due to surface tension forces. In this presentation, we review the fluid-ejection methods used by animals across scale. We demonstrate mammals shake at tuned frequencies to dry their fur, generating 10 - 70 times earth's gravity. Smaller flying insects remove accumulated water drops by performing controlled falls or by vibrating their wings at twice the frequencies of in-flight flapping. To urinate, small animals such as rats use dripping, while large mammals such as elephants use jetting.  We report urination duration is independent of animal size among animals that use jetting.  We rationalize urination styles, along with the constant-time scaling, by consideration of the relative magnitudes of the driving forces, gravity and bladder pressure, and resisting forces including viscosity and surface tension.