If a lawn sprinkler is submerged and made to suck water in instead of spray it out, which way does it spin?
#fluid-dynamics
Post a problemWhy does liquid poured slowly from a spout often dribble down the outside of the spout instead of falling cleanly into the cup?
Why does a drying drop of coffee (or any particle-laden liquid) leave a dense ring stain at its edge rather than a uniform spot?
Why can a thin falling stream of shear-thinning liquid (like shampoo) spontaneously leap upward off the pool it lands in?
Why do small floating objects like breakfast cereal clump together at the edge of a bowl of milk?
Why do tea leaves stirred into a cup collect at the center of the bottom rather than being flung outward to the rim?
Why do the bubbles in a freshly poured glass of Guinness appear to sink downward near the glass wall instead of rising?
Why does a thin sheet of water spreading out from a falling stream on a flat surface suddenly jump to a thicker, turbulent ring at a fixed radius?
Why does a liquid drop hitting a dry surface sometimes splash into a crown of droplets and sometimes spread out smoothly instead?
Why does a thin stream of honey or syrup poured onto a surface coil up like a rope instead of falling straight down?
How do baby water striders generate enough thrust to skate across water when their legs move too slowly to create the surface waves that classical theory said were needed?
Why does a shower curtain billow inward and cling to a bather when the shower is running?
Why does coffee in a mug slosh out and spill specifically when carried while walking, often after a fairly predictable number of steps?
Why does an air bubble rising through water often not go straight up but instead zigzag or spiral once it grows past a certain size?
What determines whether a flat stone thrown at a water surface will skip, and what throwing angle gives the most bounces?
Why do clear droplets or 'legs' of liquid form and slide down the inside of a wine glass above the surface of the wine?
Does the direction a draining bathtub or sink swirls depend on hemisphere (Coriolis force), as commonly claimed?
Why does a falling flat card or leaf sometimes flutter side to side, sometimes tumble end over end, and sometimes fall steadily, depending on its shape?
Why does a flag (or any flexible sheet) in a steady wind start to flap periodically instead of staying still or moving smoothly?
What inside a finger joint produces the popping sound when you crack your knuckles?