Under some conditions, hot water freezes faster than cold water, and scientists still argue about why.
The Mpemba effect is named after a Tanzanian schoolboy who noticed in 1963 that his hot ice-cream mix froze before his classmates' cooler ones. Aristotle had described something similar 2,000 years earlier.
Why is this true?
Proposed explanations include evaporation, convection currents, dissolved gases and supercooling, and some careful experiments fail to find the effect at all. It remains a genuinely open question in everyday physics.
More facts in this category
More about science & nature
Science and nature supply facts that feel like they break the rules until you see the mechanism. Hot water freezing before cold, glass that flows, lightning hotter than the surface of the Sun. Each entry keeps the physics or chemistry short and readable, states plainly where the effect is still debated, and links to a source for anyone who wants the full derivation rather than the headline.