FYFD

Tag: electrostatic charge

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    Explosively Jetting

    Dropping water from a plastic pipette onto a pool of oil electrically charges the drop. Then, as it evaporates, it shrinks and concentrates the charges closer and closer. Eventually, the strength of the electrical charge overcomes surface tension, making the drop form a cone-shaped edge that jets out tiny, highly-charged microdrops. Afterward, the drop returns to its spherical shape… until shrinkage builds up the charge density again. This microjetting behavior can carry on for hours! (Video and image credit: M. Lin et al.; research preprint: M. Lin et al.)

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    Morphing Particle Rafts

    A layer of tiny glass beads sitting atop a pool of castor oil becomes a morphing surface in this video. Applying an electric field creates enough electrostatic force to draw the interface upward against the power of both gravity and surface tension. Moving the electric field — either by shifting the electrode or simply moving a finger over the surface — is enough to pull columns of fluid along! I could imagine this making some very cool human-machine interfaces one day. (Image and video credit: K. Sun et al.)

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    Flying Spiders Use Electric Fields

    Many species of spider fly with a technique calling ballooning. We’ve touched on spider flight before, but more recent research adds a new dimension to the phenomenon. Researchers showed that spiders can actually use electrical fields in their flight. When isolated from flow or outside electrical fields, researchers found that spiders would still begin ballooning behaviors when subjected to electrical fields similar to those found in nature. The spiders were even able to take off in the artificial environment, using the electrostatic force between the surrounding fields and their negatively charged silk strands. While electrical fields alone were enough to get spiders aloft, the team thinks spiders in nature likely still use a combination of electrostatic force and aerodynamic drag in order to travel the vast distances spiders have been known to cover. (Video and image credit: BBC; research credit: E. Morley and D. Robert)

  • Jumping Frost

    Jumping Frost

    Liquid water is easily electrically charged, due to its polar nature. That’s why rubbing a comb is enough to deflect a stream of water. Ice is harder to charge, but it can happen, especially when there are temperature gradients across the ice.

    That’s the key behind this study of jumping frost. When ice crystals grow on a surface much colder than their surroundings, positive charges gather in the colder region, leaving the dendritic branches of the ice negatively charged. When researchers brought liquid water near the charged ice crystals, the water became charged, too. Positive charges in the water attracted the negatively-charged dendrites, causing the ice crystals to jump off the surface.

    Studies like this help us better understand cloud and rain formation and may one day lead to new ways of de-icing surfaces. (Image credit: frost – Miriams-Fotos, figure – R. Mukherjee et al.; research credit: R. Mukherjee et al.; via ChemBites; submitted by Kam-Yung Soh)

    Figure showing snapshots of dendritic ice as it jumps off a surface due to electrostatic charge.
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    Kelvin’s Thunderstorm

    In this video, Derek Muller explains how an experiment known as Lord Kelvin’s thunderstorm generates electricity from falling water. The set-up relies on a positive feedback loop that creates a separation of charge between the two streams of water. Check out the video for a great demonstration and explanation. If you prefer your science with a more dystopian flavor, there’s a second version of the video made in collaboration with the Hunger Games movies.  (Video credit: Veritasium; submitted by entropy-perturbation)

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    Dribbling Droplets

    Ethanol droplets on a hot copper plate bounce under the influence of electrostatic forces from a charged rod. The temperature of the plate is high enough that the droplet is supported by a thin vapor film, which is what keeps it from wetting the plate.  Ethanol does not have the strong polarity that water does, but the hydroxyl group on one end does make it susceptible to the electrostatic charge built up on the teflon rod.  As a result, the droplets oscillate under electrostatic and gravitational forces, resulting in a dribbling effect. (Video credit: S. Wildeman et al.)