Law of Urination: 21 Sec Urination Across Mammals

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Discussion Overview

The discussion centers around the "Law of Urination," which posits that all mammals empty their bladders in an average duration of 21 seconds, regardless of size. The scope includes theoretical and experimental aspects of urination across various mammal species, examining the hydrodynamics involved and potential implications for understanding urinary systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants reference a study that claims all mammals urinate over a duration of approximately 21 seconds, highlighting the evolutionary adaptations of the urinary system.
  • Others express skepticism about the study's completeness, suggesting that factors such as beer and coffee consumption were not controlled for in the research.
  • One participant mentions age and enlarged prostate as additional factors that could influence urination duration.
  • A later reply humorously notes that the study may lack scientific value due to the focus on humor and the absence of certain variables.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the study's validity, with multiple competing views regarding the completeness of the research and the influence of external factors on urination duration.

Contextual Notes

Limitations include the lack of control for variables such as beverage consumption and the potential impact of age and health conditions on urination duration.

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Law of Urination: all mammals empty their bladders over the same duration
Patricia J. Yang, Jonathan C. Pham, Jerome Choo, David L. Hu
http://arxiv.org/abs/1310.3737

The average duration, in mammals of varying sizes, of urination is 21 seconds.

Abstract:

The urinary system evolved to eject fluids from the body quickly and efficiently. Despite a long history of successful urology treatments in humans and animals, the physics of urination has received comparatively little attention. In this combined experimental and theoretical investigation, we elucidate the hydrodynamics of urination across five orders of magnitude in animal mass, from mice to elephants. Using high-speed fluid dynamics videos and flow-rate measurement at Zoo Atlanta, we discover the "Law of Urination", which states animals empty their bladders over nearly constant duration of average 21 seconds (standard deviation 13 seconds), despite a difference in bladder volume from 100 mL to 100 L. This feat is made possible by the increasing urethra length of large animals which amplifies gravitational force and flow rate. We also demonstrate the challenges faced by the urinary system for rodents and other small mammals for which urine flow is limited to single drops. Our findings reveal the urethra evolved as a flow-enhancing device, enabling the urinary system to be scaled up without compromising its function. This study may help in the diagnosis of urinary problems in animals and in inspiring the design of scalable hydrodynamic systems based on those in nature.
 
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I don't think this study is complete. They didn't control urination duration for beer consumption.
 
SteamKing said:
I don't think this study is complete. They didn't control urination duration for beer consumption.
Or coffee - with or without beer. :smile:
 
Every experimentalist on PF starts to look for his stopwatch.
 
Age and/or an enlarged prostate are two other factors.
 
Note: std dev == 13 seconds. Except for the beer problem, which most mammals do not have, I think this handles old age and prostate issues. Plus when pelvic matters were evolving, I'm pretty sure we can flatly state 'early hominids did not brew beer'.

Oh well, so much for any scientific value in the thread... Humor, yes. Note that all the humor seems to have arisen from the male sector of PF'ers. It's all good -- Mozart loved potty humor, too.
 
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