FYFD

Search results for: “surface tension”

  • Polygonal Jumps

    Polygonal Jumps

    Hydraulic jumps occur when a fast-moving fluid enters a region of slow-moving fluid and transfers its kinetic energy into potential energy by increasing its elevation.  For a steady falling jet, this usually causes the formation of a circular hydraulic jump–that distinctive ring you see in the bottom of your kitchen sink. But circles aren’t the only shape a hydraulic jump can take, particularly in more viscous fluids than water. In these fluids, surface tension instabilities can break the symmetry of the hydraulic jump, leading to an array of polygonal and clover-like shapes. (Photo credits: J. W. M. Bush et al.)

  • The Archer Fish’s Arrows

    The Archer Fish’s Arrows

    The archer fish hunts by shooting a jet of water at insects in the leaves above and knocking them into the water. How the fish achieve this feat has been a matter of contention.  A study of high-speed video of the archer’s shot shows that fluid dynamics are key.  The fish releases a pulsed liquid jet, imparting greater velocity to the tail of the jet than the head.  As a result, the tail tends to catch up to the head and increase the jet’s mass on impact while decreasing the duration of impact.  Simultaneously, the jet tends to break down into droplets via the Rayleigh-Plateau instability caused by surface tension.  Surface tension’s power to hold the water in droplets combined with the inertial effects of the pulsed jet create a ball of fluid that strikes the archer’s prey with more than five times the power than vertebrate muscles alone can impart. For more on archer fish, check out this video and the original research paper by A. Vailati et a. (Photo credits: Scott Linstead and BBC; submitted by Stuart R)

  • Featured Video Play Icon

    “Ferienne”

    In “Ferienne” artist Afiq Omar utilizes ferrofluids, magnetism, and vibration to create analog visual effects. Most of the dot and labyrinthine patterns result from the reaction of a ferrofluid submerged in a nonmagnetic fluid to an external magnetic field.  Diffusion effects and surface tension instabilities are also visible in the way the darker ferrofluid breaks down in the carrier fluid. Also be sure to check out Omar’s previously featured fluid film “Ferroux”. (Video credit: Afiq Omar)

  • Featured Video Play Icon

    Microgravity Water Balloons

    When a water balloon pops in microgravity, waves propagate from the initial point of contact and the final point of contact (where the balloon skin peels away).  As these waves come inward toward one another, the water is compressed from its original potato-like shape into a pancake-like one. In most cases, surface tension will provide a damping force on this oscillatory motion, eventually making the water into a sphere. On Earth, in contrast, a water balloon seems to hold its shape after popping.  This is because the effect of gravity on the water is much larger than the effect of the propagating waves. This is one reason that it is useful to have a laboratory in space! Without a microgravity environment, it is much harder to study and observe secondary and tertiary-order forces on a physical event. (Video credit: Don Pettit, Science Off The Sphere)

  • Shark-Tooth Instability

    Shark-Tooth Instability

    A viscous fluid inside a horizontally rotating circular cylinder forms a shark-tooth-like pattern along the fluid’s free surface. This is one of several patterns observed depending on the fluid’s viscosity and surface tension and the rotational rate of the cylinder. (Photo credit: S. Thoroddsen and L. Mahadevan; for more, see Thoroddsen and Mahadevan 1996 and 1997)

  • Falling Oil

    Falling Oil

    A drop of silicone oil falling through a liquid with lower surface tension distorts into multiple vortex rings connected by thin films. This behavior is caused by the interaction between viscous and capillary forces and is observable for only a narrow range of oil viscosities. (Photo credit: A. Felce and T. Cubaud)

  • Homemade Astronomy

    Homemade Astronomy

    Artist Julia Cuddy uses liquids, soaps, and glitter to create photographs that replicate the look of deep space astronomy. By adding soap to the dyes, she uses Marangoni effects to drive surface tension instabilities that cause swirling colors and motions reminiscent of galaxies and nebulae. Although I’ve seen fluid dynamics used in art before, this may be one of the cleverest usages I’ve seen! (Photo credits: Julia Cuddy)

  • Featured Video Play Icon

    Astro Puffs

    Microgravity continues to be a fascinating playground for observing surface tension effects on the macroscale without pesky gravity getting in the way. Here astronaut Don Pettit has created a sphere of water, which he then strikes with a jet of air from a syringe. Initially, the momentum from the jet of air creates a sharp cavity in the water, which rebounds into a jet of water that ejects one or more satellite drops.  Surface waves and inertial waves (inside the water sphere) reflect back and forth until the fluid comes to rest as a sphere once more. Note how similar the behavior is to the pinch-off of a water column. Both effects are dominated by surface tension, but on Earth we can only see this behavior with extremely small droplets and high-speed cameras! (Video credit: Don Pettit, Science Off the Sphere)

  • Featured Video Play Icon

    Pinch-Off

    This high-speed video reveals a fascinating bit of kitchen sink physics.  When a water droplet pinches off from the nozzle, the thin filament of fluid that connected the droplet to the water on the nozzle often breaks off as well.  Surface tension snaps the filament together into a sphere, causing wild oscillations and even ejection of microjets in the tiny satellite droplet. (Video from S. Thoroddsen et al. 2008’s Annual Review)

  • Featured Video Play Icon

    Soap Film Loops

    Here’s a fun demonstration of the effects of surface tension. If a loop of thread is dropped onto a soap film, as shown above, popping the soap film inside the thread will pull the thread into a circle.  This is because the surface tension of the soap film outside the thread is reacting to the sudden loss of the balancing force exerted by surface tension inside the thread loop. Surface tension arises from intermolecular forces in a fluid.  Because those forces are in balance except along the interface of a fluid–where the fluid molecules are not completely surrounded by identical molecules–there is a net force exerted at the surface.

More posts