The document summarizes the Mpemba effect, where warmer water sometimes freezes faster than colder water. It describes the effect's history, proposed explanations, and variables that affect outcomes. These include freezing method, definition of "frozen," container properties, and temperature measurement. The authors conducted an experiment demonstrating the effect and found the initially warmer samples froze first. While insulation from early frost formation was initially proposed as the cause, videos suggest it may not fully explain the phenomenon. The causes remain unclear and an area of ongoing research.

1. The Mpemba Effect: An Overview
Cian McElhinney
Émer Jones
Jonathan McKeon
Cian Tuohy

2. What is the Mpemba Effect?
 The Mpemba effect is the observation that, in
certain specific circumstances, warmer water
freezes faster than colder water.
 Has never been conclusively explained and
baffles scientists.
 Several physical conditions have been
associated with the effect.

3. History and Origin:
 Phenomenon observed by Aristotle, Francis
Bacon and René Descartes.
 Aristotle observed ‘antiperistasis’; ‘the
supposed increase in the intensity of a quality
as a result of being surrounded by its
contrary quality’.
 Term ‘Mpemba effect’ originated in the
1960’s.

4. Erasto B. Mpemba:
 Tanzanian high-school student.
 Noticed effect while doing a school cookery
assignment in 1963.
 Enquired about the effect during a seminar
given by Dr. Denis G. Osborne.
 Osborne was sceptical at first but researched
and confirmed Erasto’s findings.
 The duo published the combined results of
their research in 1969.

5. Definition Of “Mpemba Effect”
“Hot water freezes quicker than
cold”
 As “Mpemba Effect” isn't very well
defined or limited to a specific
definition, there are many variables
which we fell is one of the main
reasons it hasn’t been scientifically
proven to date.

6. Variables
 Method Of Freezing
 Definition of Freezing
 Container Type & Size
 Method of taking temperature

7. Method Of Freezing
 Slow freezing
 Non-frost-free refrigerator (-14°C)
 Frost-free refrigerator (-14°C)
 Ice container with salt (-6°C)
 Fast freezing
 Cold liquid (e.g. Liquid Nitrogen -196°C)
 Cold outside temperature (North/South,
Pole −70°C)

8. Definition of ‘Frozen’:
 Point at which water forms a visible surface
layer of ice.
 Point at which the entire volume of water
becomes a solid
 Point at which the temperature ,at any point,
reaches 0°C
 Point at which the temperature of entire
volume is 0°C or lower.

9. Container Type & Size
 Type
 Use of plastic/glass/Pyrex or metal.
 As all these materials have different
thermometric properties and
physicals (conductivity and type of
surface)
 Size
 Changes surface area in contact
with air/container

10. Method of taking temperature
 Digital
 IR, Thermocouple probe -accurate-
 Non-Digital
 Mercury, Alcohol thermometer -not
as accurate-
 Thermometer/probe may influence
freezing as they may move or have
ice form around them.

11. What causes the effect?
 There is no generally accepted cause.
 Causes we proposed:
 Insulating effect of frost/ice & Convection
currents.
 Hotter liquids Molecules.
 Evaporation of the warmer liquid.
-Loss of mass
-Change in pressure
 Quality of water (Solutes)- impurities
 Supercooling observed more in cold water

12. Insulating effect of Frost/Ice and
Convection currents
 The cooler water will to freeze from the
top, reducing further heat loss by
radiation and air convection
 The warmer water will freeze from the
bottom and sides because of water
convection.

13. Igloos: The Insulating Effect of Ice
 Temperature outside (approx. 57°C)
Inside can still be quite comfortable.

14. Hotter liquids Molecules
 Hotter liquids molecules are more
excited than colder ones.
 When the water molecule is
excited it vibrates and becomes
unstable,
 It then wants to release energy to
become stable.

15. Evaporation of the warmer liquid:
-Loss of mass
 As the warmer liquid evaporates its
mass decreases. -This may have
been the case for Erasto Mpemba.-
 But there has been several further
experiments using a coating of oil or
a lid on the container to prevent
loss of mass by evaporation.

16. Evaporation of the warmer liquid:
-Change in pressure
“Liquid freezes at higher
temperatures with higher pressure.”
 Covering the container will mean
there will be different pressure
levels in each container.
 Container with the hotter liquid may
have a greater pressure.

17. Triple point of water
 The combination of pressure and
temperature at which liquid water,
solid ice, and water vapour can coexist
in a stable equilibrium occurs at
exactly 273.16 K (0.0098 °C) at
atmospheric pressure.
 The change in pressure can change
this point.

19. Quality of water (Solutes)- impurities
“Increasing the number of dissolved
particles lowers freezing point.”
 Boiling the water may remove
impurities such as bacteria and
other objects that may be
suspended or dissolved in the liquid.

20. Supercooling
 Pure water normally freezes at
273.15 K (0 °C) but it can also be
"supercooled" at standard pressure
down to 231 K (−42 °C).

21. Our Experiment:
 Objectives
 To demonstrate the effect
 To investigate the possible causes of
the effect
 Variables
 Method of freezing
 Definition of ‘frozen’.
 Container type and size
 Method of measuring temperature

22. Method:
 Began with three beakers of water at
different temperatures. (1=3.9°C
2=19.2°C 3=35.2°C)
 Immersed the beakers in a trough of slush
(Ice & salt at -6°C).
 Used electronic thermometers and an
automatic graphing device to record
temperature of beakers and slush.
 Determined freezing point using a light and
a camera.

24. Observations
 12 min – Beaker 1 froze on surface
only.
 17 min – Surface Tension on Beaker
2+3 “skin” of the water curving
around probes.
 34 min – Beaker 2 instantaneously
froze
 38 min – Beaker 3 instantaneously
froze

25. Weights at end of experiment
 Beaker 1 – 40.75-32.5=9.25

Beaker 2 – 44 - 32.5 =11.5
 Beaker 3 – 43.25-32.5=10.75

26. Conclusion:
 We successfully demonstrated the Mpemba
effect.
 The initially warmer water samples froze
before the five-degree sample.
 The five-degree ice sample weighed the
least.
 We feel that this effect is due to a number
of reasons but the main one is “The
Insulating effect of Frost/Ice”

27. Videos
 But “The Insulating effect of Frost/Ice” has
been proven to not be the main cause as
seen in 1st
video.
 http://www.youtube.com/watch?v
=xOVZV6DxaRs @ 1.20, 1.59 & 2.30 min.