FYFD

Tag: water bottle flip

  • Stopping a Bottle’s Bounce

    Stopping a Bottle’s Bounce

    A few years ago, the Internet was abuzz with water bottle flips. Experimentalists are still looking at how they can arrest a partially fluid-filled container’s bounce, but now they’re rotating the bottles vertically rather than flipping them end-over-end. Their work shows that faster rotating bottles have little to no bounce after impacting a surface.

    This image sequence shows how water in a rotating bottle moves during its fall (top row) and after impact (bottom row). Water climbs the walls during the fall, creating a shell of fluid that, after impact, forms a central jet that arrests the bottle's momentum.
    This image sequence shows how water in a rotating bottle moves during its fall (top row) and after impact (bottom row). Water climbs the walls during the fall, creating a shell of fluid that, after impact, forms a central jet that arrests the bottle’s momentum.

    The reason for this is visible in the image sequence above, which shows a falling bottle (top row) and the aftermath of its impact (bottom row). When the bottle rotates and falls, water climbs up the sides of the bottle, forming a shell. On impact, the water collapses, forming a central jet that shoots up the middle of the bottle, expending momentum that would otherwise go into a bounce. It’s a bit like the water is stomping the landing.

    The authors hope their observations will be useful in fluid transport, but they also note that this bit of physics is easily recreated at home with a partially-filled water bottle. (Image and research credit: K. Andrade et al.; via APS Physics)

  • Water Bottle Flipping Physics

    Water Bottle Flipping Physics

    Water bottle flipping has become quite the craze, and in a recent video The Backyard Scientist presented his own take on the subject, testing whether you could flip a bottle with mercury rather than water. As it turns out, fluid dynamicists have studied this topic, too, by dropping partially-filled elastic spheres containing water, isopropyl alcohol, and glycerin. The key physics here comes from the sloshing of liquid inside the container.  When the elastic ball bounces, energy that would otherwise go into the sphere’s rebound instead gets distributed into sloshing the fluid inside. The result is that the sphere bounces less on its subsequent impacts.

    Interestingly, the researchers found that the properties of the fluid inside the ball made very little difference to its rebound height. Instead, the most important feature was the volume of fluid in the container. Balls filled to approximately 30% of their volume had the most damping – that’s totally consistent with the best water bottle flips, which use bottles about 1/3rd full.

    The main difference between flipping a bottle and dropping a ball is what goes on in the first bounce. When a bottle hits a surface, the liquid inside has already been disturbed by the bottle’s rotation. For a ball being dropped, that first impact is what disturbs the fluid. So while a water-filled ball’s first rebound will reach nearly the same height as an empty ball, the spinning water bottle is, in effect, already on its second bounce. The motion of the fluid inside the bottle acts as a damper, allowing the bottle to stick the landing. (Image credit: Mercury Bottle Flip – The Backyard Scientist, source; Water Ball Bounce – The Splash Lab, source; research credit: T. Killian et al.)