What actually makes ice slippery enough to skate on: pressure melting, friction heating, or an intrinsically liquid-like surface layer?
#partly-solved
Post a problemWhy does a liquid drop hitting a dry surface sometimes splash into a crown of droplets and sometimes spread out smoothly instead?
Why does a shower curtain billow inward and cling to a bather when the shower is running?
What inside a finger joint produces the popping sound when you crack your knuckles?
Why does a spun coin or disk settling flat on a table spin faster and faster, with the clatter rising in pitch, right up to the instant it stops?
What determines the propagation speed of a wave of toppling dominoes, and why does it approach a roughly constant value regardless of how hard the first domino was pushed?
Why do snow crystals always grow with six-fold symmetry, and why is no two snowflakes exactly alike?
Why does a cold squash ball barely bounce, while the same ball bounces energetically once warmed up by play?
Why does a drying layer of mud or paint crack into a network of roughly polygonal (often near-hexagonal) plates?
Why, when a container of mixed different-sized granular particles (like nuts or cereal) is shaken, do the largest particles reliably rise to the top rather than settling based on density?
How do migratory animals like birds, sea turtles, and some fish sense Earth's magnetic field well enough to navigate across continents or oceans, and does this rely on a genuinely quantum-mechanical process inside a light-sensitive protein in their eyes?
Liquid nitrogen is around -196 C, yet a small splash on bare skin often causes no injury at all: what protects the skin, and when does that protection fail?
Why does a plastic shower curtain often billow inward toward the water spray and stick to your legs while you shower, instead of staying put or blowing outward?
Why does burning firewood make crackling, popping, and hissing sounds, and why is the noise so much louder and more frequent with some pieces of wood than others?
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?
How does a beetle living in one of the driest deserts on Earth collect enough drinking water from fog on its back?
Why do some smooth, spinning balls at intermediate speeds curve in the direction opposite to what the ordinary Magnus effect predicts?
Why did several NASA and ESA spacecraft (including Galileo, NEAR, Cassini, and Rosetta) show small unexplained changes in speed (a few mm/s) during close Earth gravity-assist flybys in the 1990s-2000s, beyond what standard orbital mechanics predicts?
Can nuclear fusion reactions be harnessed in a reactor that produces more usable energy than it consumes, for practical power generation?
How do rod- or disk-shaped molecules self-organize into the partially ordered liquid-crystal phases, and what microscopic physics produces ferroelectric materials with a switchable spontaneous electric polarization?