Mpemba Effect β Hot Water Freezes First
A water mystery still not fully solved
In 1963, Tanzanian middle school student Erasto Mpemba noticed something strange during an ice cream making class. His hot sugar mixture froze before another student's cold mixture.
The teacher said he was wrong. But Mpemba kept questioning, and later asked physics professor Denis Osborne about it. Osborne said "I don't know, let's test it" β and confirmed that hot water indeed froze first in some cases.
Why Does This Happen
There's no consensus explanation yet. Major hypotheses:
Evaporation hypothesis: Hot water evaporates, reducing its volume. Less water freezes faster. Simple, but doesn't explain all experimental results.
Convection hypothesis: Hot water has active convection currents. The circulation makes heat transfer more efficient.
Hydrogen bond hypothesis: Claims that hydrogen bond structure differs in hot water. Recent research shows interest but nothing conclusive.
Dissolved gas hypothesis: Hot water has less dissolved gas (heating drives gas out). This difference may affect ice formation.
Hard to Reproduce
The tricky part: it doesn't always reproduce. Container shape, freezer conditions, water impurities β too many variables. That's why the debate has continued for over 50 years.
How It Works
Place hot water in freezer (comparison: same amount of cold water)
Evaporation, convection, hydrogen bonds etc. accelerate heat loss
Under certain conditions, hot water freezes first (not always)