#surfaceroughness — Public Fediverse posts

How Insects Fly in the Rain

Getting caught in the rain is annoying for us but has the potential to be deadly for smaller creatures like insects. So how do they survive a deluge? First, they don’t resist a raindrop, and second, they have the kinds of surfaces water likes to roll or bounce off. The key to this second ability is micro- and nanoscale roughness. Surfaces like butterfly wings, water strider feet, and leaf surfaces contain lots of tiny gaps where air gets caught. Water’s cohesion — its attraction to itself — is large enough that water drops won’t squeeze into these tiny spaces. Instead, like the ball it resembles, a water drop slides or bounces away. (Video and image credit: Be Smart)

#biology #butterfly #cohesion #droplets #fluidDynamics #hydrophobic #insects #physics #science #superhydrophobic #surfaceRoughness #surfaceTension

Morphology, Timing, And Drivers Of Post-Glacial Landslides In The Northern Yellowstone Region
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https://doi.org/10.1002/esp.5943 <-- shared paper
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#GIS #spatial #mapping #spatialanalysis #spatiotemporal #geomorphometry #geomorphology #massmovement #landslides #elevation #slope #triggers #water #hydrology #engineeringgeology #slopefailure #remotesensing #LiDAR #seismogenic #climatechange #glacial #sediments #YellowstoneNationalPark #Yellowstone #temporal #risk #hazard #mitigation #prediction #stratigraphy #surfaceroughness #debuttressing #Pleistocene #Holocene #moisture #historic #erosion #undercutting #records #fieldwork #mountains #deglaciation

Soft materials tend to be sticky, and once they’re adhered to a surface, they’re often harder to remove than they were to attach — think of Scotch tape stuck to a desk. This difficulty separating sticky things — known as adhesion hysteresis — has been attributed to various causes, like energy lost to viscoelasticity or age-related chemical bonding. But a new study shows that both those explanations are unnecessary.

Instead, the difficult removal comes from the way two surfaces separate in fits and starts. No two surfaces are perfectly smooth, and soft surfaces are able to conform to all the nooks and crannies of their partner surface. That molding results in a lot of surface contact, all of which must break for the materials to detach. That peeling doesn’t take place smoothly. Instead, the two surfaces part a little at a time in discrete jumps, as shown in the image above. The colors in the illustration show how much energy is dissipated in each jump, with darker colors indicating higher energy. The team found that this stick-slip mechanism is enough to account for the struggles we have un-sticking objects. They’re now looking at how water affects these narrow meeting places between sticky surfaces. (Image and research credit: A. Sanner et al.; via Physics World)

https://fyfluiddynamics.com/2024/05/unsticking-in-jumps/

#adhesion #fluidDynamics #physics #science #solidMechanics #stickSlip #surfaceRoughness

machinist rule of thumb question : if you can feel a scratch with a fingernail how deep must it be? (i’ve not hit on a good search string) #machining #SurfaceRoughness #ScratchAndSniff