|
|
| Line 1: |
Line 1: |
| {{Refimprove|date=December 2009}}
| | Emilia Shryock is my name but you can call me anything you like. His family members life in South Dakota but his wife wants them to transfer. The favorite hobby for my children and me is to play baseball but I haven't made a dime with it. For years I've been operating as a payroll clerk.<br><br>My web site: [http://www.mygcci.org/node/12088 over the counter std test] |
| In the study of [[animal locomotion on the surface layer of water]], '''Denny's paradox''' refers to the apparent impossibility of surface-dwelling animals such as the [[water strider]] generating enough propulsive force to move. It is named after [[Mark Denny]].
| |
| If [[capillary waves]] are assumed to generate the momentum transfer to the water, the animal's legs must move faster than the [[phase speed]] <math>c_m</math> of the waves, given by
| |
| :<math>c_m=\left(4g\sigma/\rho\right)^{1/2}</math>
| |
| where <math>g</math> is the [[standard gravity|acceleration due to gravity]], <math>\sigma</math> is the strength of [[surface tension]], and <math>\rho</math> the [[density]] of [[water]]. For standard conditions, this works out to be about 0.23 m/s.
| |
| | |
| Infant water striders' legs move at speeds much less than this and, according to this physical picture, cannot move.
| |
| | |
| Writing in the [[Journal of Fluid Mechanics]], David Hu and John Bush state that Denny's paradox "rested on two flawed assumptions. First, water striders' motion was assumed to rely on the generation of capillary waves, since the propulsive force was thought to be that associated with [[wave drag]] on the driving leg. Second, in order to generate capillary waves, it was assumed that the strider leg speed must exceed the minimum wave
| |
| speed, <math>c_m=\left(4g\sigma/\rho\right)^{1/2}\simeq 0.23</math>m/s. We note that this second assumption is strictly true only for steady motions".<ref name="Bush 2010">{{cite journal|author=David L. Hu|coauthor=John W. M. Bush| title=The hydrodynamics of water-walking arthropods| journal=[[Journal of Fluid Mechanics]]| year=2010| volume=644| pages=5–33}}</ref>
| |
| | |
| ==References==
| |
| {{reflist}}
| |
| | |
| {{DEFAULTSORT:Denny's Paradox}}
| |
| [[Category:Physical paradoxes]]
| |
| [[Category:Locomotion (biological)]]
| |
Emilia Shryock is my name but you can call me anything you like. His family members life in South Dakota but his wife wants them to transfer. The favorite hobby for my children and me is to play baseball but I haven't made a dime with it. For years I've been operating as a payroll clerk.
My web site: over the counter std test