FYFD

Tag: splashes

  • London 2012: Diving Physics

    London 2012: Diving Physics

    Divers twist and spin gracefully in the air, but the highest marks come when they enter the water with little to no splash. This rip entry–named after paper-ripping sound characteristic of such a dive–is possible thanks to fluid dynamics.  Any time a solid object enters a still liquid, it tears a cavity into the liquid. The smaller this cavity is, the less the liquid will rebound and splash when the cavity gets refilled. In diving, achieving a small splash requires a couple items. First, the diver will grab his hands over his head to form a flat surface. This will create the initial small cavity through which his body follows. When entering, the diver will keep his body straight and rigid, with arms pressed against his head; this adds stability to keep the diver from letting the force of striking the water at 35 mph affect his body’s form and create splash.  Finally, the perfect dive enters vertical to the water surface. This ensures that all of the diver’s body finds its way into that cavity created by the hands without striking any undisturbed water. Once under the water, divers often extend their arms to generate enough drag to slow down quickly.  All in all, the rip entry minimizes the cavity size and thus the splash, adding a great exclamation point to a beautiful dive. (Photo credits: Associated Press, Adam Pretty/Getty Images, Nigel Wade, Jed Jacobsohn)

    FYFD is celebrating the Olympics by featuring the fluid dynamics of sport. Check out our previous posts on how the Olympic torch works, what makes a pool fast, the aerodynamics of archery, the science of badminton, and how cyclists “get aero”.

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    How Mosquitoes Fly in the Rain

    One might think that rainfall would keep the mosquitoes away, but it turns out that rain strikes don’t bother these little pests much.  Because the insect is so small and light compared to a falling raindrop, the water bounces off instead of splashing. This results in a relatively small transfer of momentum, although the mosquito does get deflected quite strongly. Researchers estimate that the insects endure accelerations up to 300 times that of gravity, which is more than 10 times what a human can withstand. (Video credit: A. Dickerson et al; submitted by Phillipe M.)

  • Splash Rebound

    Splash Rebound

    A ball dropped onto a puddle loses some of its rebound momentum to fluid motion.  On impact, a splash curtain and radial jet form as the fluid is displaced by the ball.  As the ball rebounds, the splash curtain is drawn inward into a column of fluid drawn up by the ball, reminiscent of the way cats and dogs drink.  Eventually, when the gravity’s force on the fluid column overcomes the force of the ball’s inertia, the fluid column pinches off and falls back downwards, leaving the ball free to utilize its remaining kinetic energy as it flies upward. (Photo credit: T. Killian, K. Langley, and T. Truscott)

  • Floral Still Life

    Floral Still Life

    Fluid motion is captured as a floral still life in these high-speed photos by Jack Long. The artist keeps mum about his set-up but notes that these are single capture events, not constructed composites. It looks as if the blossoms are created from the impact of a falling fluid with the upward jet that forms the stem. The leaves and vase appear to be created from upward splashes, but whether those are generated by vibration or dropping an object is unclear. See Long’s Flickr page for more. (Photo credit: Jack Long via Gizmodo)

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    Hydrophobic Water Entry

    Many factors can affect the size and shape of the splash when an object impacts water and wettability–the ability of a liquid to maintain contact with a solid–is one of them. Here a sphere coated in a hydrophobic (water-repellent) nano-layer impacts water, creating a large air, streaky air cavity and a substantial splash.  Contrast this with the behavior of a hydrophilic sphere entering the water, and you can imagine divers might want to invest in some hydrophilic coatings prior to the London Olympics. (Video credit: L. Bocquet et al)

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    Granular Eruptions

    Granular flows, which are made up of loose particles like sand, often display remarkably fluid-like behavior. Here researchers explore the behavior of granular flows when a solid impacts them at high speed. The sand, unlike a fluid, does not have surface tension, yet we still observe many of the same behaviors. Like a fluid, the sand splashes and creates cavities and jets as it deforms around the fallen object. The sand even “erupts” as submerged pockets of air make their way back to the surface.

  • Seed-Ejection via Raindrop

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    We don’t often think of plants as using fluid dynamics aside from capillary action drawing water from their roots, but many plants also use fluid dynamics to disperse reproductive materials.  This high-speed video explores the efficacy of splashing raindrops at ejecting seeds from different blossoms. (Video credit: G. Amador et al)

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    Tempus II

    While not strictly fluid mechanical Philip Heron’s Tempus II features some great slow-motion action of fluids. (Submitted by @ftematt)