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Sticky Physics

As anyone can tell you, certain liquids, like water, will usually fall in droplets while others, such as honey, will slowly slide to the ground in a long filament. The key differences between these two liquids are viscosity and surface tension, and scientists have conducted a new experiment to better understand these differences. Volcanoes, ink-jet printers, and archer fish—who use their mouth as a sharpshooting water pistol to hunt prey—all take advantage of the properties of liquid filaments and droplets.



In their study, scientists from Cambridge University created liquid streams ranging from pure water to pure glycerol, a naturally-occurring compound used to sweeten food and manufacture glue. The researchers then used a high-speed camera to record the various substances as they fell to the ground. From this data, the scientists could determine specifically what variations in viscosity and surface tension led to streams forming droplets or pinching off. The experiment provided a verification of previous models, but the data also navigated uncharted territory with the wide selection of previously untested liquids.

With this new data, scientists hope to improve upon several applications that depend heavily on differences in viscosity and surface tension. In ink-jet printing, for example, the printer shoots a stream of ink at high speeds onto the paper, requiring just the right type of liquid to avoid blotting.

Also, patients receiving certain respiratory medicines rely on liquid droplets as opposed to streams. Only small enough droplets can be absorbed in the lungs, so this type of research can help doctors better administer these types of drugs.

This research on fluid dynamics will be published in a forthcoming article in the journal Physical Review Letters.

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