FYFD

Tag: water entry

  • Urinal Dynamics Win Ig Nobel Prize

    Urinal Dynamics Win Ig Nobel Prize

    Thirteen years ago, I made a prediction that work on how to avoid urinal splashback would win an Ig Nobel Prize. Today, I am, at last, vindicated. Randy Hurd, Zhao Pan, Tadd Truscott, and Kaveeshan Thurairajah shared the 2026 Ig Nobel Prize in Physics for their work designing a splash-free urinal.

    The culmination of this decade-plus of research are two urinal designs, the Cornucopia (“Cornucopeea”) and the Nautilus (“Nauti-Loo”). Both designs minimize splash, in part, through their geometry. As you may have noticed when rinsing dishes, having a stream of droplets hit a surface at a high impact angle creates lots of splash. But at a low impact angle, very little splash occurs. The team took this observation and created designs that minimized impact angle no matter where a user aimed.

    How splashback varies with impact angle. High and medium impact angles (left and middle, respectively) generate a lot of splashing from a stream of impacting droplets. In contrast, below a critical impact angle, the splashing is negligible (right).
    How splashback varies with impact angle. High and medium impact angles (left and middle, respectively) generate a lot of splashing from a stream of impacting droplets. In contrast, below a critical impact angle, the splashing is negligible (right).

    Naturally, they tested the two new designs, alongside two existing urinal designs, finding that the new urinals reduced splashing by as much as 95% across a range of flow rates and user heights. Although the Cornucopia was the least splashy urinal, the team gave the Nautilus an overall edge because its design is easier to clean and works for children, adults, and wheelchair users.

    Considering the estimated 1 million liters of urine contemporary urinals splash across U.S. restrooms daily, the Nautilus could save significant labor and cleaning costs, if implemented. (Image credits: urinals and experiment – K. Thurairajah et al., poster – R. Hurd et al.; research credit: K. Thurairajah et al. and R. Hurd et al.)

    P.S. – As indicated, I’ve followed this work for a long time. In addition to this post, we did a webcast (10 years ago, yikes!) that touched on the topic. But my most in-depth coverage of the story is still to appear in print; you’ll get to enjoy the whole tale–stretching all the way back to 2012–in a chapter of my forthcoming book. More on that soon! In the meantime, please enjoy this gem of a scientific poster from the project’s early days in 2013:

    One of the best research posters of all time, designed to look like it's been written on a tiled bathroom wall. The text reads, "Confessions of a Sitzpinkler. Though Sitzpinklers, men who sit to urinate, are held in low-esteem within the male community, they have reasonable scientific justification for their actions. Due to the Plateau-Rayleigh instability, a simulated average male urine stream breaks into droplets approximately 15-20 cm after emerging from the urethra. For a typical male and toilet, the opening of the urethra is 13 cm or less above the surface of the water when sitting. The urine stream does not fully transition into droplets before it enters the water as shown in the image on the left. This stream-surface interaction causes bubble entrainment and limited splashing. The resulting satellite droplets lack the necessary momentum to rise above the rim of a typical toilet, not to mention that they toilet bowl is covered when sitting. In contrast, the average male urinates from a standing height of 64 cm above the water surface with the urine stream breaking into droplets 44-49 cm above the water surface. In the image on the right, the rapid procession of droplets impacts the surface violently, creating splash curtains, deep cavities and jets. These dynamic events collectively contribute to the emission of relatively high-momentum satellite droplets, capable of traversing beyond the rim of a typical toilet bowl. Sitzpinklers around the world should rest easy knowing that the hygienic benefits of sitting during urination far outweigh the negative social implications."
    One of the best research posters of all time, designed to look like it’s been written on a tiled bathroom wall. The text reads, “Confessions of a Sitzpinkler. Though Sitzpinklers, men who sit to urinate, are held in low-esteem within the male community, they have reasonable scientific justification for their actions. Due to the Plateau-Rayleigh instability, a simulated average male urine stream breaks into droplets approximately 15-20 cm after emerging from the urethra. For a typical male and toilet, the opening of the urethra is 13 cm or less above the surface of the water when sitting. The urine stream does not fully transition into droplets before it enters the water as shown in the image on the left. This stream-surface interaction causes bubble entrainment and limited splashing. The resulting satellite droplets lack the necessary momentum to rise above the rim of a typical toilet, not to mention that they toilet bowl is covered when sitting.

    In contrast, the average male urinates from a standing height of 64 cm above the water surface with the urine stream breaking into droplets 44-49 cm above the water surface. In the image on the right, the rapid procession of droplets impacts the surface violently, creating splash curtains, deep cavities and jets. These dynamic events collectively contribute to the emission of relatively high-momentum satellite droplets, capable of traversing beyond the rim of a typical toilet bowl.

    Sitzpinklers around the world should rest easy knowing that the hygienic benefits of sitting during urination far outweigh the negative social implications.”
  • Featured Video Play Icon

    Wavy Water Entry

    When an object like a sphere enters the water, it drags air into the water behind it, creating a cavity. Depending on the sphere’s impact speed, the cavity might close first under the water, forming a deep seal, or at the surface with a surface seal. But, as this video points out, water often isn’t still. Here, they explore how the sphere’s entry changes when there are ripples on the water surface. (Video and image credit: M. Ibrahim et al.; via GFM)

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  • “Immersion”

    “Immersion”

    Some seabirds, including gannets and boobies, feed by plunge diving. From high in the air, they fold their wings and dive like darts into the water, impacting at speeds around 24 m/s to help them reach the depths where their prey swim. With their narrow beaks and necks, the critical moments in this feat come when the bird’s head is submerged but its body remains out of the water. At this point, the bird’s head is decelerating quickly and its body is still moving at full speed; if the neck cannot withstand this combination of forces, it will buckle.

    But plunge divers, it turns out, have a secret weapon that helps them handle impact: their head shape. A study of water entry dynamics using 3D-printed models of birds’ heads found that plunge divers have a shape that increases the amount of time it takes to enter the water. The impact forces stretch out over that longer period of contact, which also stretches out the time it takes for the bird to reach its maximum deceleration. The end result? That extended contact time protects birds from unsafe levels of deceleration, just like a crumple-zone in a crashing car keeps its occupants from experiencing the worst decelerations. (Image credit: K. Zhou/BPOTY; research credit: S. Sharker et al.; via Colossal)

  • Curved Rocks Hit Harder

    Curved Rocks Hit Harder

    Intuition suggests that a flat rock will hit the water with greater force than a spherical one, and experiments uphold that. But a flat rock, interestingly, doesn’t produce the greatest impact force. Instead, it’s a slightly curved rock that experiences peak impact forces. Researchers found this happens because of the thin layer of air that coats the front of the impacting object. For flat faces, this layer is relatively thick and provides a cushioning effect that reduces the peak force and spreads out the impact. In contrast, a slightly curved convex surface traps a thinner air layer, and that lack of cushioning maximizes the impact force. (Image credit: J. Wixom; research credit: J. Belden et al.; via APS Physics)

  • Paris 2024: Diving

    Paris 2024: Diving

    In competition diving, athletes chase a rip entry, the nearly splash-less dive that sounds like paper tearing. Part of a successful rip dive comes in the impact, where divers try to open a small air cavity with their hands that their entire body then enters. But the other key component happens below the surface, where divers bend at the hips once underwater. This maneuver enlarges the air cavity underwater and disrupts the formation of a jet that would typically shoot back upwards. Done properly, the result is an entry with little to no splash at the surface and a panel full of pleased judges. (Image credits: top – A. Pretty/Getty Images, other – E. Gregorio; research credit: E. Gregorio et al.; via Science News; submitted by Kam-Yung Soh)

    Sequence of images showing a synthetic diver bending underwater to disrupt splash formation.
    Sequence of images showing a synthetic diver bending underwater to disrupt splash formation.

    Related topics: Rip entry physics, how pelicans dive safely, and how boobies plunge dive

    This post marks the end of our Olympic coverage for this year’s Games, but if you missed any previous entries, you can find them all here.

  • Diving Together

    Diving Together

    Two spheres dropped into water next to one another form asymmetric cavities. A single ball’s cavity is perfectly symmetric, and so are two spheres’, provided they are far enough apart. But for close impacts, the spheres influence one another, creating a mirror image. The same asymmetric cavity also forms when a sphere is dropped near a wall. In fluid dynamics, this trick — using two mirrored objects in place of a wall — is used to make calculating certain flows easier! (Image credit: A. Kiyama et al.)

  • Tokyo 2020: High-Dive Physics

    Tokyo 2020: High-Dive Physics

    In Olympic high-diving, athletes leap from a maximum of 10 meters above the water. Although the force of their water impact is substantial, it’s small enough that they can enter the water head first. For cliff divers — who may jump from 27 meters! — the impact force is too great to risk a head-first entry, so they enter the water feet first. But this does not eliminate their risk of injury.

    As the diver’s body enters the water, each leg creates its own cavity, and the proximity of the two cavities generates a repulsive force. If the diver isn’t prepared to resist that force, it will force their legs apart, potentially injuring them. (Image and research credit: T. Guillet et al.)

  • Brace For Impact

    Brace For Impact

    What happens in the moment before an object hits the water? That’s the question at the heart of a new study exploring how water deforms before an object’s impact. The researchers dropped circular disks onto a pool of water and, using a new reflection-based technique, measured micron-sized deflections in the water’s surface before impact, as seen below.

    Animation showing the deflection of the water's surface just before a circular disk impacts it.
    Movie of the water surface’s deflection as the circular disk approaches. Look for distortions in the grid pattern.

    The deflections are caused by the air getting squeezed out of the space between the oncoming object and the water surface. The team found that the deformation isn’t uniform. The air squeezing out along the edges moves fast enough to trigger a Kelvin-Helmholtz instability and actually pull up the water surface. So when the disk hits, it impacts along its edges first and traps an air bubble underneath. (Image credits: divers – E. Carter, experiment – U. Jain et al.; research credit and submission: U. Jain et al.)

  • The Two-Faced Splash

    The Two-Faced Splash

    The way a sphere enters water depends on its size, speed, and surface properties. A hydrophilic (water-attracting) sphere behaves differently than a hydrophobic (water-repelling) one. But what happens when the object’s surface properties aren’t uniform?

    That’s the situation we see above. The dark line marks the two hemispheres of the sphere and their differing surface properties. To the left, the sphere is hydrophilic; to the right, it is hydrophobic. When the sphere hits the water, both the splash and underwater cavity quickly become asymmetric. On the hydrophobic side, the cavity wall is smooth, but the cavity is rough on the hydrophilic side. In the end, the asymmetries create a horizontal force that pushes the sphere sideways. (Image and research credit: D. Watson et al.)

  • Featured Video Play Icon

    Viscoplastic Drop Impact

    There are many materials that don’t behave exactly as a fluid or a solid, instead displaying characteristics of both. In this video, we see drops of hair gel falling into water. The gel is viscoplastic – showing some of the viscous behavior of a fluid and some of the plastic behavior (the inability to change back to its initial shape) of a solid.

    On impact, the gel deforms due to the forces on it, but the final shape does not depend solely on the amount of force; instead, it’s the rate at which the forces are applied that determines the final shape. By tuning the impact speed and the gel stiffness, it’s possible to make many final capsule shapes, something that could be useful in applications like drug manufacturing. (Image and video credit: M. Jalaal et al.)