Which freezes faster — cold water or boiling water? It can happen, as Erasto B. Mpemba discovered in 1967 when he was a form-3 student (equivalent to North American 11th grade) making ice cream at Magamba Secondary School in Lushoto, a small town in Tanzania, Africa.
Erasto asked his science teacher to explain why his hot milk froze faster than a friend's cold milk. The teacher said, "You were confused; that cannot happen." Erasto must have had some reservations about this reply because, over the next couple of years, he asked the same question of two more physics teachers, finally finding one with an open mind.
Erasto's day of discovery started like most school days. He woke up before dawn. Pulling on his school-uniform navy-blue shorts, he shivered in the cold. But the afternoon would be hot, this close to the equator, even though he was almost a mile high in the mountains. "I've time to make ice cream," he thought, and set out for milk.
He strode briskly along the dirt main street of Lushoto to the open-air market. Quickly he bought some milk, and headed back to school. He mixed sugar with milk, and put the pot on the stove to boil. It had begun to boil, when he noticed another boy not bothering to heat his mixture in order to seize space in the refrigerator's freezing compartment. Erasto grabbed the last available space, putting his boiling-hot liquid beside the cool one.
"The other boy and I went back in an hour and a half later, and found that my tray of milk had frozen into ice-cream while his was only a thick liquid, not yet frozen," Erasto wrote later. Erasto asked his physics professor why, and got only 'that cannot happen' answer.
Two years later, in Mkwawa High School, Erasto again asked why the hot liquid froze faster than the cold. His new teacher answered: You were confused.
But help was coming. The school's headmaster invited physicist Dennis Osborne of the University College in Dar es Saalam to lecture and answer questions. Erasto asked his question yet again.
Dr. Osborne smiled into Erasto's earnest face. "Is it true, have you done it?"
"Yes."
Everyday events are seldom as simple as they seem, mused Osborne to himself. "I do not know, but I promise to try this experiment." And he did, eventually getting similar results. Osborne found cold water near 20 degrees C (70 F) began to freeze in about 100 minutes; whereas hot water about 80 degrees C (175 F) began to freeze much quicker — in 40 minutes.
Further Reading:
The Mpemba Effect (aka Cool?) by E.B. Mpemba and D.G. Osborne, published first in 1969 and reprinted in 1979: Phys. Educ. 1969 4 172-5, Phys. Educ. 1979 14).
Can hot water freeze faster than cold water? by Monwhea Jeng, University of California
Hot water freezing by Rod Nave, HyperPhysics, Georgia State University
Supercooling and the Mpemba effect, The Smithsonian/NASA Astrophysics Data System Knight, Charles A., The Mpemba Effect: The Freezing Times of Hot and Cold Water, Letter in Am J Phys, Vol 64, May 1996, p524
Auerbach, David, Supercooling and the Mpemba Effect: When Hot Water Freezes Faster Than Cold, Am J Phys. 63, 882-885, (1995)
J. Walker, "The Amateur Scientist", Scientific American, vol. 2337, #3, pgs 246-7, Sept. 1971)
kweli sijawahi kuona watanzania tumefikia hapa!! haya ni mafanikio makubwa na ni challenge kubwa kwa wataalamu wetu wa bongo. Unapoitwa mwanafizikia, mwanasayansi, professor wa eneo fulani, ni LAZIMA uoneshe u-professor wako kivitendo!! Ninajivunia kupata sasa mtanzania aliyegundua kitu katika physics!!! ''MPEMBA EFFECT''.Inauma sana maana tangu mtanzania mwenzetu alipogundua hii kitu mwaka 1967!!! hakuna effort yoyote iliyofanyika kumuenzi na hata kuchochea ugunduzi mwingine wowote katika eneo lolote!! Wanafunzi mlioko masekondari, wanafunzi mlioko vyuoni, waalimu na wataalamu wengine- huu ni wito wangu mkuu kwenu, tuwajenge vijana wetu ili wawe wataalamu wa kweli na sio wataalamu wa kwenye mitihani!!!
ReplyDeleteNinaumia sana sana maana nami niko katika eneo hili na sijafanya chochote kuletea maendeleo nchi yangu. Kila siku huwa najiuliza ni lini nitaifanyia kitu nchi yangu... nakosa jibu, BUT I STILL HOPE AND BELIEVE no sooner, i will do something good for the betterment of my country and my fellow tanzanians. MUNGU IBARIKI NCHI YANGU NZURI YA TANZANIA, MUNGU ONGEZA UJUZI KWA WATANZANIA ILI TUKATUMIKE KWA AJILI YA MAENDELEO YA WATANZANIA WENZETU NA NCHI YETU.
DJM
You can see more recent developments in:
ReplyDeleteEsposito,S., De Risia, R. and Somma,L. (2008) Mpemba effect and phase transitions in the adiabatic cooling of water before freezing; Physica A: Statistical Mechanics and its Applications; Volume 387, Issue 4, 1, Pages 757-763
Jeng, M. (2006) The Mpemba effect: When can hot water freeze faster than cold? American Journal of Physics, Volume 74, Issue 6, pp. 514-522
However, it is important to reflect on the sort of motivation this landmark theory has our emerging scientists and the way it has been promoted across the world - surely, not much impact is felt from within and that is a shame. Here is another challenge:
Most tribes across the country believe in witchcraft in which one's health may be tampered with through black magic. Typically, bewitching involves getting acess to human body bio-products such as hair, saliva, urine, stool or body fluids. Modern day genomics is based on DNA samples of the same material! What is the link? Could the traditional witchcraft and healing be based on an hitherto DNA technology which lost its traits only to be re-discovered and formalised in the last few generations? Couldn't someone with witchcraft powers (with access to a potential victim's DNA information) alter the DNA sequence to cause deformity even before a baby is born? Apology to those who do not believe in witchcraft - both my religion and culture acknowledge it and I am just trying to link it up to my scientific understanding.
Bravo Mpemba!
ReplyDeleteHii ndo akili
Hivi kwanini watu kama hawa Tanzania..hatuwaproud, mi nimesoma masomo ya sayansi O level and A level..but to be honnest I never heard this...aisee shukrani sana..imebidi niingie ktkt google nisome vizur theory..na habari ya huyu jamaa...mnaweza cheki ktkt hii link http://forgetomori.com/2008/skepticism/mpemba-science/. Jamani TZ we need to change..watu kama hawa wanaitajika kujulikana..na almost kila mtanzaina...unajua kitendo cha kujulilkana kwake, kunachochea chachu ya wanafunzi kuwa wadadis..kama "Mpemba did this so we also can do some thng". Na mi najua kuna watu TZ they are very good, but motisha hakuna.
ReplyDeleteNilijaribu kugoogle na kukuta wakisema hii effect haijapewa uzito sana sababu haitokei wakati wote,na ha yeye mpemba mwenyewe na Dr. Osborne hawakueleza kwanini iyo effect inatokea.japo miaka ya hivi karibuni ya 2000 kuna sababu zimejulikana kwanini inatokea ivyo na hivyo kujibu swali kwanini haitokei wakati wote.
DeleteKUONGEZEA TOKA KTK COMMNT ILIYOPITA.....Tunahitaji tuwe na events ktk shule za vitu kama hizi. najua kuna shule huwa wanakuwa na sayansi day mfano...ktkt sayansi day tujaribu kutoa history za watu kama hawa au kuwaalika kutoa lecture kidogo, its very helpful kwa wanafunzi..i'm saying this bcause through histories, watchng documentaries za vitu kama hivi, kwangu mimi imenisaidia sana kujenga interest ya vitu navyosoma..na ukijenga interest for sure kuelewa kitu haiwi ngumu.....na sio upande wa sayansi tu hata masomo mengine..mfano ishu za economy, kuna watu kama Christopher Mwakasege apart frm huduma za mahubiri..i knw he is very good ktk ishu za uchumi. Invite watu kama hawa kutoa lecture japo once in a while mashuleni vyuoni..Inabidi tutumie vichwa vyetu kuproduce vichwa zaid...THANKS!!!!!
ReplyDeleteWabongo tulivyo "si anajidai ana akili tutaona", utakuta anavuta mkokoteni au choka ile mbaya. Tunaozesha akili ambayo ingetusaidia maishani tunakalia ufisadi tuu.
ReplyDeletewatanzania wapo vichwa, hebu mwangalieni mwingine huyu: http://www.mwananchi.co.tz/newsrids.asp?id=11052
ReplyDeleteNime google na kuona vitu vya mpemba, jamaa nimemkubali, lakini, sijaelewa vizuri alichokigundua. msaada kwenye tuta. the fact kwamba hot water freezes faster than cold water ilikuwepo toka kipindi cha aristtle. Msaada kwenye tuta.
ReplyDeleteWatu kama Mpemba tunao mashuleni na kwenye vyuo vyetu. Kinachokosekana ni mipango ya kusaidia na kukuza watu wenye vipaji ambavyo si vya kawaida. Wenye uwezo wa kusaidia watu kama Mpemba hawafanyi hivyo na badala yake wako tayari kutoa mamilioni na hata zawadi za magari kwa washindi wa mambo kama ya Miss World, Miss Universe, Miss Earth n.k eti kwa kuwa na sura au umbo zuri nakutembea chukwaani kwa mbwembwe na kichupi !!
ReplyDeleteTunaona ni bora kuwaenzi na kuwapa motisha hao.
Nafurahi kusikia hii maana si muda mrefu professor alitoa mfano wa mpemba theory and since i was from tanzania i was asked if i knew anything abt it and didn't.Been curious since then and now kusoma hii imenifanya nifurahi and going to tell pro abt it.Thought Mpemba was Pemba, apparently it was his last name.uuuhhh thanks for posting this
ReplyDeleteShame to ministries of education, science and technology. Watanzania roho mbaya sana.
ReplyDeleteKama wengine mnavyosema inabidi tubadilike. Nakumbuka nilikuwa namchallenge sana mwalimu wangu wa Economics sana (uzuri alikuwa ni msomi kwelikweli kwa hiyo hakuwa offended) lakini ukikutana na mbabaishaji atakukatisha tamaa tu. Nadhani mentality hiyo ya kuchallenge conventional wisdom ni vizuri tuki-instill kwenye watoto na vijana itasaidia kama kweli tunataka mapinduzi ya kisayansi, kiuchumi na kijamii.
ReplyDeleteWatu wenye vichwa wapo Tanzania ila sielewi kwa nini wanafichwa.
Hivi Mpemba yuko wapi? Nakumbuka walikuwa wanamzungumzia nikiwa nasoma Zanaki Seconmdary late 70's. Kweli tuna ma-genius, lakini wako wapi? Kuna kijana ambaye alikuwa anapiga hesabu haraka kuliko calculator tena namba kubwa kubwa, sijui naye kaishia wapi.
ReplyDeleteanony wa 11:01:00 uliuliza "the fact kwamba hot water freezes faster than cold water ilikuwepo toka kipindi cha aristtle"
ReplyDeleteMpemba ndio alikuwa wa kwanza kufanya angalizo juu ya suala hilo. Ni kwamba waliomtangulia walikuwa hawajaliona hilo. Ni kama tunavyosema Newton aligundua kani-mvuto ya dunia (earth's gravity). Sio kwamba ye ndio aliyeitengeneza, na "gravity" ilikuwepo toka enzi na enzi, ila Newton ndio alikuwa wa kwanza kuweza kueleza ni kwanini tufani likianguka toka mtini linaenda chini badala ya kwenda juu. Na akawa wa kwanza kukokota mchepuko wa dunia (9.8m/s^2).
Nakubaliana na mdau aliyesema kwamba unapouliza maswali mengi au kuwa mdadisi walimu wababaishaji watakukatisha tamaa na kukuita we mjuaji. Hii imewakuta wengi mashuleni.