Have you ever heard about this
concept...?
Before telling you the
concept, I want to convey you the words of Mpemba after his
discovery......because its worth to read it once....so read till the end if you
really want to catch up the interesting thing and how a normal kid turned into
a researcher.....!!!
“My name is Erasto B
Mpemba, and I am going to tell you about my discovery, which was due to
misusing a refrigerator.”
Read it again.....do you
notice the words " .....I am going to tell you about my discovery,
which was due to misusing a refrigerator" .
Ofcourse, it is an accidental
incident which lead for the discovery of a mystery concept.......!!!!
Okay....what is Mpemba
Effect...???
It is the theory that warmer
water can freeze faster than colder water under certain circumstances.
The effect has been noted
since ancient times but scientists have struggled to explain why it
occurs....From here onwards, it is a selected copy paste work from the
published article of Mpemba Effect....so forgive it....
The story of the discovery, and the
consequent mystery, is worth a bit of exploration — and the Mpemba effect
carries numerous important lessons about the nature and method of scientific
discovery.
Mpemba made his accidental discovery in Tanzania in 1963,
when he was only 13 years old and in secondary school. In spite of
widespread disdain from his classmates, he surreptitiously continued
experiments on the phenomenon until he had the good fortune in high school to
interact with Professor Denis Osborne of the University College Dar es Salaam.
Osborne was intrigued, carried out his own experiments, and in 1969 the
two published a paper in the journal Physics Education.
This article is, in my opinion, one of the
most remarkable in all of the history of physics. Aside from its title,
“Cool?”, it is also unusual in being presented in two parts: Mpemba gives a
first person account in his own words of his discovery in the first half, and
Osborne picks up the story and describes the follow-up experiments in the
second half. Mpemba’s own account is so charming and fascinating that it
is worth quoting from liberally:
My
name is Erasto B Mpemba, and I am going to tell you about my discovery,
which was due to misusing a refrigerator. All of you know that it is
advisable not to put hot things in a refrigerator, for you
somehow shock it; and it will not last long.
In
1963, when I was in form 3 in Magamba Secondary School, Tanzania, I used
to make ice-cream. The boys at the school do this by boiling milk,
mixing it with sugar and putting it into the freezing chamber in the
refrigerator, after it has first cooled nearly to room temperature. A lot
of boys make it and there is a rush to get space in the refrigerator.
One
day after buying milk from the local women, I started boiling it. Another
boy, who had bought some milk for making ice-cream, ran to the
refrigerator when he saw me boiling up milk and quickly mixed his
milk with sugar and poured it into the icetray without boiling it; so that
he may not miss his chance. Knowing that if I waited for the boiled
milk to cool before placing it in the refrigerator I would lose the
last available ice-tray, I decided to risk ruin to the refrigerator on
that day by putting hot milk into it. The other boy and I went back an
hour and a half later and found that my tray of milk had frozen into
ice-cream while his was still only a thick liquid, not yet frozen.
I
asked my physics teacher why it happened like that, with the milk that was
hot freezing first, and the answer he gave me was that “You were
confused, that cannot happen”. Then I believed his answer.
Here we have the beginnings of a classic story
of science — an accidental discovery, scoffed at by the “establishment
scientists”.
Mpemba might have given up at that point, but
he encountered a friend who sold ice cream for a living, and that friend
happened to mention that many vendors would use boiling water to make their ice
cream! It was already common knowledge amongst them, apparently, that a
boiling mixture could freeze quicker.
After
passing my O level examination, I was chosen to go to Mkwawa High School in
Iringa. The first topics we dealt with were on heat. One day as our
teacher taught us about Newton's Law of
Cooling, I asked him the question, “Please, sir, why is it that when
you put both hot milk and cold milk into a refrigerator at the same time,
the hot milk freezes first?” The teacher replied: “I do not think
so, Mpemba.” I continued: “It is true, sir, I have done it myself” and he
said: “The answer I can give is that you were confused.” I kept on
arguing, and the final answer he gave me was that: “Well, all I can say
is that that is Mpemba’s physics and not the universal physics.” From then
onwards if I failed in a problem by making a mistake in looking up the
logarithms this teacher used to say: “That is Mpemba’s mathematics.”
And
the whole class adopted this, and anytime I did something wrong they used to
say to me “That is Mpemba’s…”, whatever the thing was.
Here the high school teacher failed miserably
— ridiculing a student is pretty much the worst thing one can do in a science
classroom! Fortunately, Mpemba was not deterred:
Then
one afternoon found the biology laboratory open, and there was no teacher. I
took two 50 cm³ beakers, one I filled with cold water from the tap and the
other with hot water from a boiler and quickly put them in the freezing
chamber of the laboratory refrigerator. After one hour I came back to look
and I found that not all the water had been changed into ice, but that
there was more ice in the beaker which had hot water to start with than in
the one which had cold water. This was not really conclusive. So,
I planned to try it again when I had the chance.
Before he had this chance, however, Professor
Osborne came to lecture on physics, giving Mpemba a valuable opportunity:
When
Dr Osborne visited our school we were allowed to ask him some questions,
mainly in physics. I asked: “If you take two similar containers
with equal volumes Of water, one at 35 °C and the other at 100 °C,
and put them into a refrigerator, the one that started at 100 °C freezes
first. Why?” He first smiled and asked me to repeat the question. After
I repeated it he said: “Is it true, have you done it?” I said: “Yes.”
Then he said: “I do not know, but I promise to try this experiment when I
am back in Dar es Salaam.” Next day my classmates in form six were
saying to me that I had shamed them by asking that question and that my
aim was to ask a question which Dr Osborne would not be able to answer.
Some said to me: “But Mpemba did you understand your chapter on
Newton’s law of cooling?” I told them: “Theory differs from practical.”
Some said : “We do not wonder, for that was Mpemba’s physics.”
There are many remarkable points in this short
passage. First of all, we see an admirable open-mindedness of Professor
Osborne in his dealings with Mpemba, and that open-mindedness would quickly
benefit them both. Conversely, we see a dangerous “groupthink” amongst
Mpemba’s classmates regarding science, in which they are genuinely offended by
Mpemba questioning the status quo. Mpemba shows great wisdom in his
answer: “Theory differs from practical”. This is an important point for
anyone studying physics: we like to create simplified models to explain nature,
but those models often lose real-world aspects in the process of stripping them
down.
Mpemba actually continued his experiments in a
kitchen refrigerator, with the permission of kitchen staff, and convinced his
classmates and the headmaster of his school of the accuracy of his findings.
At Dar es Salaam, Osborne was true to his word
and looked into the phenomenon himself. As he notes in the continuation
of the paper,
It
seemed an unlikely happening, but the student insisted that he was sure of the
facts. I confess that I thought he was mistaken but fortunately remembered the
need to encourage students to develop questioning and critical attitudes. No
question should be ridiculed. In this case there was an added reason
for caution, for everyday events are seldom as simple as they seem and it
is dangerous to pass a superficial judgment on what can and cannot be. I
said that the facts as they were given surprised me because they appeared
to contradict the physics I know. But I added that it was possible that the
rate of cooling might be affected by some factor I had not considered.
Osborne sets a great example for all physics
educators! It can be difficult at times, but “No question should be
ridiculed” would be a great part of a “Hippocratic oath” for teachers.
What happened after was the thing which got the place in the history book....!!!!
Some people who argued for the existence of a
Mpemba effect in the 13th century, and in the 17th century. But
it was Mpemba and Osborne, however, who brought it to the attention of modern
science.
After the deep confusion of 40+ years, a team
of scientists in Singapore believe they have finally revealed the mystery of
the Mpemba Effect and it lies in the unique properties of the bonds that hold
water together....!
Thank You for reading till the last...take a
deep breath, it is over....!!!!
