When a raindrop hits the inside of a Chrysosplenium echinus flower, it gathers speed, collects a few seeds, and jets back out of the 10-cm-tall plant, landing as far as a meter away. All short-stemmed Chrysosplenium and Mazus plants use so-called splash-cups to disperse their seeds like this, taking advantage of the power of raindrops in areas that are prone to frequent showers, spritzes from waterfalls, or seasonal downpours. Now, scientists have analyzed the physics of splash-cups to figure out just how these flowers speed up and launch out drops of water. By building a model of the splash-cups and taking high-speed video of water hitting it (above), the researchers found that the steepness and curvature of the flowers' walls is what propels the water so fast and so far. And the primary determinant of how much the flower sped up any individual raindrop was how far from the center of the splash-cup the drop hit, the team reports online today in the Journal of the Royal Society Interface. An understanding of how to optimize the splashes could lead to better inkjet printers and blood splash pattern analysis techniques, and could help researchers develop ways to harvest energy from rain.
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