For liquids that would ordinarily “bead up” rather than spread out on a surface, a thin layer of air intervenes below the spreading edge of the liquid sheet, so the liquid lifts off of the surface. The next step depends on the specific liquid-surface interaction. 28 meters per second, the ethanol drop splashes because it is above the splash threshold speed. It’s been long known that faster-moving drops fragment more readily than slower-moving ones and that other important factors include the drop size, liquid viscosity, and strength of the surface tension. For example, researchers would like to know whether or not such impacts will produce a splash. Industrial problems such as inkjet printing and coating of surfaces require a deep understanding of the impact of drops on solids. The results may lead to better understanding of systems such as ink jets and dispersal of pesticides and plant infections.
They performed experiments with a range of liquids and worked out an equation that predicts the minimum velocity for a droplet to splash, depending on its size and the properties of the surrounding atmosphere. Now a team in Spain says that the gas surrounding the droplet appears to be crucial to whether it splashes or not.
But researchers don’t know which factors determine the result. When a liquid drop hits a solid surface, like a raindrop hitting pavement, it may flatten and spread smoothly, or it may produce a ragged-edged splash. 47 meters per second and breaks up into a splash. 3 times the viscosity of water hits a solid surface at 2. 86-millimeter drop of silicone oil with 1.
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