MPEMBA EFFECT

1. MPEMBA EFFECT Why does hot water freeze faster than cold water? Proposed explanation by Robert Bilinski

2. INTRODUCTION • Improvised experiments arecarried out with different variablesbeing altered in order to find an explanation for the Mpemba Effect. • From these tests and background reading, a hypothesis based around convection currents isconceived. • Finally, possible experiments to verify the hypothesis are considered.

3. FREEZER EXPERIMENTS • Experiments were undertaken (in an admittedly amateurish fashion) using a kettle, a domestic freezer, two identical glass containers, a measuring jug and a watch. H C • The experiments used different variations of temperatures and volumes of water. Freezer experiment demonstration: Hot (H) and cold (C) containers with equal volumes.

4. RESULTS • The effect was observed for all variety of volumes of water except the smallest volumes. • The smallest volumes of water in the containers had roughly the same surface area as the larger volumes but relatively very little height. • The effect was not observed when the initial temperature difference between the two volumes of water was relatively large.

5. DISCUSSION • Both volumes of water at different temperatures were equal and therefore the surface area appears not to be a factor. • However, if the effect was not observed in only the smallest volumes (within the approximately cylindrical containers) then the height of the water may be a factor. This may suggest convection effects are an explanation.

6. CONVECTION CURRENT HYPOTHESIS • From the experiments conducted, the MpembaEffect is most likely due to the convection currents produced in a body of water. • Convection currents are produced when the warmer, and therefore less dense, water rises due to gravity. This produces a non-uniform temperature distribution in the water. • These currents rapidly become more exaggerated in the initially warmer water because of the greater rate of initial heat loss (even in an insulated container). • The initially warmer water has a greater temperature distribution throughout its volume which allows it to lose heat at a greater rate than the initially cooler water.

7. CONVECTION CURRENT HYPOTHESIS • This effect appears to be limited by the temperature difference between two bodies of water. Mpemba Effect observed when initial temperatures are relatively close. Mpemba Effect not observed when initial temperature difference is too great. • It appears that the convection currents can only produce the Mpemba Effect up to a limit of initial temperature difference.

8. TESTS FOR VERIFICATION • To confirm the veracity of this hypothesis, a variety of different containers would need to be tested in order to exaggerate or reduce the effects of convection currents. • A variety of containers of equal volumes but different heights could be tested in order to keep the mass of water constant…

9. TESTS FOR VERIFICATION • …And containers of different heights but the same cross-sectional area would vary the mass of water but keep constant the top surface area from where there is locally warm water and therefore greater heat loss.

10. TEST IN SPACE! • Alternatively, at a point in space away from any large masses, the effects of gravity can be considered negligible. • As a result, a test conducted here would not exhibit convection currents. Therefore, if the Mpemba Effect was still observed then this hypothesis would be falsified. (Although this may be easier said than done!) (Background photo source: http://spacefellowship.com/news/art18641/missing-primitive-stars-outside-milky-way-uncovered.html)

11. CONCLUSION • From improvised experimentation, the Mpemba Effect is determined to probably be due to convection currents. This aids heat loss because of the non-uniform temperature distribution. • An initially warmer volume of water is affected by greater convection currents than the initially cooler water and therefore loses heat much faster. • This effect appears to be limited by the initial temperature difference between the two bodies of water. • To verify this hypothesis different shapes and sizes of container need to be tested. A zero-gravity environment would help!