Definition[ edit ] The phenomenon, when taken to mean "hot water freezes faster than cold", is difficult to reproduce or confirm because this statement is ill-defined. With the above definition there are simple ways in which the effect might be observed. For example, if the hotter temperature melts the frost on a cooling surface and thus increases the thermal conductivity between the cooling surface and the water container. Hence many people, when they want to cool water quickly, begin by putting it in the sun. So the inhabitants of Pontus when they encamp on the ice to fish they cut a hole in the ice and then fish pour warm water round their reeds that it may freeze the quicker, for they use the ice like lead to fix the reeds. The Scottish scientist Joseph Black investigated a special case of this phenomenon comparing previously-boiled with unboiled water;  the previously-boiled water froze more quickly.
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No comments Help discover why warm water freezes quicker than cold water. The Mpemba effect The Mpemba effect is the phenomenon where hot water freezes quicker than cold water. We received 22 entries to the competition. These were whittled down to just 11 finalists by the panel of expert judges and the public vote.
The winner of the competition, Nikola Bregovic, research assistant in the field of physical chemistry at the Department of Chemistry, University of Zagreb, Croatia, was announced on the 10th of January How the question came about A discussion between Erasto Mpemba, Dr Dennis Osborne and Ray de Souza describing how the question, "why does hot water freeze quicker than cold water? Drawing conclusions and raising further questions that could be investigated, based on their data and observations.
Using appropriate scientific language and ideas to explain, evaluate and communicate their methods and findings. Selecting and planning the most appropriate ways to answer science questions, recognising and controlling variables where necessary, including: Carrying out comparative and fair tests.
Recording data and results using scientific diagrams and labels, classification keys, tables, scatter graphs, bar and line graphs. Asking their own questions about scientific phenomena.
Learning outcomes Children will: Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius.
Concepts supported Children will learn: That materials and substances can change from one state to another, and that these changes are often reversible. That hot water freezes quicker than cold water.
Suggested activity use This resource could be used with a whole class to carry out the investigation. Children could work in small groups to carry out a simple comparative test on whether hot or cold water freezes first. This initial experiment may lead to children asking follow-up questions that they would like to investigate, e. Do all hot liquids freeze quicker than cold liquids?
Practical considerations To carry out this activity, access to a freezer would be required, and if children are working in groups, quite a large amount of freezer space is needed. Thermometers will need to be provided for children to measure the temperature of their water. Please take into account health and safety considerations, and act accordingly. Extra care and adult supervision will be required when working with hot water. Children will need to check the experiment at regular intervals to see which one freezes first.
Efecto Mpemba: ¿Por qué el agua caliente se congela más rápido que el agua fría?
¿Hay una explicación definitiva del efecto Mpemba?