FYFD

Tag: water

  • Mixing in a Winter Lake

    Mixing in a Winter Lake

    A frozen winter lake can hide surprisingly complex flows beneath its placid surface. Since water is densest at 4 degrees Celsius — just above the freezing point — mixing two water sources can lead to counterintuitive effects. A cold lake, for example, may contain water below 4 degrees Celsius, while a stream running into the lake is a bit warmer than 4 degrees Celsius. When the two parcels of water meet, they mix to form water at an intermediate temperature. But because of water’s density anomaly, that mixed water can wind up denser than the average of its parents. This is known as cabbeling.

    Mixing patterns within a cold lake with a slightly warmer inflow. Image from A. Grace et al.
    Mixing patterns within a cold lake with a slightly warmer inflow. Image from A. Grace et al.

    As shown in a recent study, this newly mixed water sinks to the bottom of the lake, forming a warm current that heats the lake from below. The researchers were able to model this current and its behavior over a range of conditions. Understanding these winter circulation patterns is key to tracking both nutrient transport and how pollutants spread in the ecosystem. (Image credit: lake – G. Murry, simulation – A. Grace et al.; research credit: A. Grace et al.; via APS Physics)

  • Nanoconfined Water

    Nanoconfined Water

    Water is a decidedly weird substance. It’s densest above its freezing point; it has a slippery liquid-like layer on its solid form; and, in the right form, it can bend like a wire. So it’s not surprising that water demonstrates some odd behaviors when it’s confined inside a space so narrow it’s only one molecule thick.

    A new, simulation-based study finds that this nanoscale-confined water flows with a wide variety of behaviors, depending on the temperature and pressure. In some conditions, the water ceases to act molecularly, with hydrogen atoms flowing through a lattice of oxygen atoms. These superionic forms were thought only to exist in the extreme conditions of a gas giant’s interior, but these simulations suggest we can find them under far milder circumstances. (Image and research credit: V. Kapil et al.; via Physics World; submitted by Kam-Yung Soh)

  • Beijing 2022: Why Are Ice and Snow Slippery?

    Beijing 2022: Why Are Ice and Snow Slippery?

    Although every Olympic winter sport relies on the slippery nature of snow and ice, exactly why those substances are so slippery has been an enduring mystery. Michael Faraday hypothesized in the nineteenth century that ice may have a thin, liquid-like layer at its surface, something that modern studies have repeatedly found.

    One recent study used an entirely new instrument to probe the characteristics of this lubrication layer and found that it is only a few hundred nanometers thick. But the fluid in this layer is nothing like the water we’re used to. Instead it has a viscosity more akin to oil and its response to deformation is shear-thinning and viscoelastic, more like the complex fluids in our kitchens and bodies than pure, simple water. They found that using a hydrophobic probe modified the interfacial viscosity even further, which finally provides a hint at the mechanism behind waxing skis and skates. 

    Fortunately for us, we’ve found plenty of ways to employ and enjoy water’s slipperiness, even as the mystery of it slowly gives way to understanding. (Image credit: M. Fournier; research credit: L. Canale et al.; via Physics World; submitted by Kam-Yung Soh)

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    Microgravity Water Spheres

    Here astronaut Don Pettit demonstrates the effects of rotation on a sphere of water in microgravity. Bubbles, being less dense than water, congregate in the middle of the sphere along its axis of rotation. Tea leaves, which are denser than the water, are thrown to the outside; this is the same concept used in a centrifuge for separating samples.

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    Water-Walking Basilisks

    Some animals, like the common basilisk (a.k.a. the Jesus Christ lizard) are capable of running across water for short distances. The basilisk accomplishes this feat by slapping the water with sufficient force and speed to keep its body above the surface. This slap also creates a pocket of air around its foot. The lizard propels itself forward by kicking its leg back, then lifting its foot out of the water before the air bubble collapses. Water birds like the Western Grebe and tail-walking dolphins rely on similar physics to stay above the water line. # (submitted by Simon H)

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    Water Drops at 10,000 FPS

    We’ve seen water droplets join a larger pool at 2,000 frames per second, but what about 10,000 frames per second? (via Gizmodo)