ERIC Number: EJ1094573
Record Type: Journal
Publication Date: 2016-Mar
Abstractor: As Provided
Investigating the Mpemba Effect: When Hot Water Freezes Faster than Cold Water
Ibekwe, R. T.; Cullerne, J. P.
Physics Education, v51 n2 Article 025011 Mar 2016
Under certain conditions a body of hot liquid may cool faster and freeze before a body of colder liquid, a phenomenon known as the Mpemba Effect. An initial difference in temperature of 3.2 °C enabled warmer water to reach 0 °C in 14% less time than colder water. Convection currents in the liquid generate a temperature gradient that causes more rapid heat loss by surface radiation and evaporation than obtains for uniform temperature. This more rapid cooling enables the initially warmer liquid to overtake the cooler liquid, reaching 0 °C earlier and freezing first. Liquid cooling under natural convection follows a five-fourths power law (temperature of liquid T, temperature of surroundings Ta, cooling constant k): dT divided by dt = k(T - T[subscript a])5 divided by 4. In this investigation we found that with evaporation this becomes a four-thirds power law: dT divided by dt = k(T - T[subscript a])4 divided by 3.
Descriptors: Science Instruction, Physics, Scientific Concepts, Thermodynamics, Heat, Water, Science Experiments
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Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
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