Why do ship wakes on deep water always form a V of the same angle (about 19.5 degrees) regardless of the ship's speed, and do very fast ships obey this?
Physics
Post a problemCan a levitating Leidenfrost droplet be made to move in a controlled direction using a ratchet-textured hot surface?
Under what conditions do large particles sink to the bottom of a shaken granular mixture instead of rising, reversing the usual Brazil-nut effect?
Why do certain sand dunes emit a loud, sustained musical 'booming' or 'singing' hum when sand avalanches down their slip face?
Why do structurally similar knots differ enormously in the force needed to make a rope slip or break, and can this be predicted?
Why do lotus leaves stay perfectly clean and water-repellent despite growing in muddy water?
How can a gecko run up a smooth vertical wall or across a ceiling without any glue or suction?
How does a beetle living in one of the driest deserts on Earth collect enough drinking water from fog on its back?
Why does cooling lava (like the Giant's Causeway) or drying mud crack into regular hexagonal columns?
What actually keeps a riderless bicycle rolling straight and stable without falling over?
How can a small spinning magnetic top hover stably in midair above a magnetic base despite Earnshaw's theorem forbidding static magnetic levitation?
How can a cat dropped upside-down with zero angular momentum twist itself around in mid-air to land feet-first, without violating conservation of angular momentum?
Why does a boomerang thrown correctly curve around and return to the thrower instead of flying straight?
Can a wind-powered vehicle sail directly downwind faster than the wind itself, and if so, how?
What actually makes the vanes of a Crookes radiometer (the light-mill in a partial vacuum) spin when light shines on it, given that Crookes's original light-pressure explanation predicted the wrong direction?
Why does a curling stone curve in the direction it is spinning, when simple friction models predict it should curl the opposite way or not curl at all?
Does a faint third-order rainbow, formed by three internal reflections inside raindrops and predicted centuries ago but never convincingly photographed in nature, actually occur?
Has a fourth-order rainbow, formed by four internal reflections inside raindrops, ever been captured in a natural photograph after more than a century of failed attempts?
What optical mechanism produces the colored rings ('glory') seen surrounding the shadow of your head or an airplane cast onto a cloud or fog bank?
Are the flashes of upward lightning-like discharges above thunderstorms that pilots reported for decades real, and what are they?