Mtanzania aliyetoa changamoto kwa Isaac Newton

[BasilSawewe]

Kazi nzuri sana ilitakiwa na yeye aandikwe kwenye ile topic ya newtons law of cooling
Kama
Mpemba challenge for newtons' law of cooling..!

Lugha ngumu sana uliyotumia bw we! Uliulizaje? Maana sikukuelewa.

Nouma sana tz ....ata mm nikiwa primary nilimuulizaga ticha why ukiweka maji ya limao kwenye shahawa soon ukimwaga uwa liquid na taste ya maji....jaribu lakini niliambulia fimbo. ....japo Kwa ss nn majibu. ..

 

[Tutor B]

Kiuhalisia alichofanya Mpemba ni kuthibitisha kivitendo, tena akiwa Form 3, Newton's law of cooling; kitu ambacho walimu wake wa sekondari (O-level na A-level) na hata huyo profesa wa chuo kikuu walikuwa hawajafanya! Walikuwa wanakariri tu! Kanuni ya Newton kuhusu kupoa inasema: "Kasi ya kitu kupoa inaathiriwa moja kwa moja na tofauti ya joto kati ya joto la hicho kitu na joto la mazingira yake". Hivyo, kwa mfano, maji yanayochemka (nyuzi 100 Celsius) yakiwekwa kwenye jokofu (nyuzi -10 Celsius) yatapoa haraka kuliko maji yenye joto nyuzi 35 Celsius yakiwekwa kwenye hilo hilo jokofu kwa sababu tofauti ya joto ni kubwa; nyuzi (100 - [-10]) = nyuzi 110 Celsius; kuliko nyuzi (35 - [-10]) = nyuzi 45 Celsius.

Sijakusoma hapo mkuu fafanua.

 

[Mgibeon]

This country bwaunah... Hii issue wangekua wamefanya WAKENYA tungeshasikia "Mkenya effect" kwenye mitaala yetu.

 

[made]

Nouma sana tz ....ata mm nikiwa primary nilimuulizaga ticha why ukiweka maji ya limao kwenye shahawa soon ukimwaga uwa liquid na taste ya maji....jaribu lakini niliambulia fimbo. ....japo Kwa ss nn majibu. ..

duh!hahahahahaha.....itabidi na ww utupe shule kidg

 

[Maguge Maguge]

Kinadharia inawezekana tukashika nafasi ya tatu au nne kisayansi duniani

Mbona hueleweki?

 

[Nyaka-One]

Nouma sana tz ....ata mm nikiwa primary nilimuulizaga ticha why ukiweka maji ya limao kwenye shahawa soon ukimwaga uwa liquid na taste ya maji....jaribu lakini niliambulia fimbo. ....japo Kwa ss nn majibu. ..

Aaah aaah. Wewe kweli ulistahili mboko. Ukiwa bado primary tayari ulishayajua hayo makitu?!

 

[mpiga era]

Ebu nasisi tujaribu kwanza hii experiment ili tujiridhishe kwanza ndipo tu reply

 

[nra2303]

Sidhani km huyu jamaa anajulikana au hiyo effect ishawahi hata kufundishwa uko vyuoni au shuleni! Nilisoma PCM na sikuwahi kuambiwa au kusoma sehemu kuhusu "mpemba effect" hii kitu ifanyiwe kazi tafadhali! Atangazwe kwa mbwembwe zote

 

[Mchizi]

Mpemba effect..huu uzi umeanzishwa mara nyingi sana humu JF. Bahati mbaya ni watu wachache hapa Tanzania wanaojua mpemba effect ni nini..Research nyingi za hii kitu zinafanywa hasa na vyuo vikuu vya nje , ingawa bado jibu sahihi halijapatikana.Scientists finally understand why hot water freezes faster than cold

 

[Kanungila Karim]

Vizuri sana

 

[Makanyaga]

Mtanzania aliyetoa changamoto kwenye kazi ya "Newton's Law of Cooling "

Kwa hisani ya rafiki yangu Mhandisi John Peter Mbunda (JPM)

“MPEMBA EFFECT”: UDADISI, UTAFITI NA UGUNDUZI WA KITANZANIA

“MAJI ya moto yaliyochemka yanaganda (kuwa barafu) haraka zaidi kabla ya maji ya baridi”.

Ni ugunduzi wa kisayansi wa Mtanzania usiotajwa kwenye Vitabuni, Shuleni wala Vyuoni mwetu hapa nchini, lakini ni gumzo la kitaaluma katika Vyuo na taasisi mbalimbali za elimu za Mataifa mbalimbali. Ni “Udhani” (Hypothesis) unaoumiza vichwa vya wanasayansi wa Dunia yote, kuanzia Ulaya Magharibi, Amerika mpaka Asia.

Ugunduzi huu wa kisayansi unaeoelezea “sifa ya kipekee ya maji” ulifanywa na mwanafunzi wa kidato cha tatu wa Kitanzania katika shule ya sekondari Magamba, Lushoto, Mkoani Tanga, mwaka 1963. Jina la Mwanafunzi huyo ni Erasto Bartholomeo Mpemba, jina ambalo sifa hiyo ya maji (physical phenomenon) imepewa, yaani “Mpemba effect”.

Erasto Batholomeo Mpemba, kama ilivyokuwa kwa wanasayansi wengine maarufu duniani, alifanikiwa kugundua sifa hii muhimu ya maji kama ajali tu (accidental discovery), kama ilivyokuwa kwa Wagunduzi wengine wa Kisayansi wa Kaliba yake, Mfano Friedrich August Kekule (Mgunduzi wa Udhani wa Umbo la Kekule katika Sayansi ya Kemia), Isaack Newton, Archemedes na wengineo, Mpemba naye amefanya ugunduzi wake baada ya tukio la kawaida tu katika maisha yake ambalo lilileta majibu yasiyo ya kawaida na yanayofikirisha.

Katika andiko mashuhuri juu ya “Mpemba Effect” lililochapishwa katika Jarida la Kitaaluma la ‘Journal of Physics Education’ la mwaka 1969, Mpemba anaanza kujieleza ifuatavyo, “Jina langu ni Erasto B. Mpemba, nitawaambia ugunduzi wangu ambao umetokana na matumizi mabaya ya jokofu”.

Masimulizi hayo ya Mpemba katika andiko hilo yanaainisha kwa undani mazingira ya elimu ya Tanzania tokea miaka ile ya mwanzo mwa Taifa letu mpaka sasa. Kikawaida wanafunzi wengi wa kitanzania wanaosema kwenye shule za umma, ama hufanya biashara za walimu wakiwa madarasani wakati wa vipindi au baada ya vipindi, au hufanya biashara za Wazazi wao. Erasto Mpemba na wenzake kadhaa pale shuleni Magamba (Hivi sasa ni Sebastian Kolowa Memorial University, SEKOMU), walikuwa wanauza ‘ice-cream’ baada ya kumaliza vipindi vya masomo.

Ingawa haijawekwa wazi kwenye masimulizi hayo kwamba, mradi huu ulikuwa wa shule ama wa mwalimu tu, lakini wanafunzi waliohusika na biashara hii walikuwa wengi, hivyo iliwabidi wagombee nafasi kwenye jokofu wakati wa kutengeneza ‘ice cream’ hizo. Kwa kawaida ilikuwa wananunua maziwa asubuhi na mapema kutoka vijiji vya jirani kama vile Maina, Mazinde Juu, Mabughai, Kost na kwengineo; wanayachemsha, wanaacha yapoe kisha wanayaweka kwenye jokofu kabla ya kwenda darasani.

Wakimaliza vipindi vyao madarasani, huchukuwa ‘ice-cream’ zao zilizoganda na kupeleka Lushoto-mjini kwa mauzo. Yule atakayekuwa kakosa nafasi ya kuweka ‘ice cream’ zake kwenye jokofu itampasa asubiri mpaka wenzake watoe ice-cream zao nyakati za mchana kwenda kwenye mauzo ndipo na yeye apate nafasi ya kuweka za kwake. Lakini pia kwa yule aliyeweka mwanzo kabla ya mwenzake, alikuwa na uhakika wa kuanza kupeleka ‘ice-cream’ zake sokoni kabla ya mwezake, maana anayeweka mwanzo ice cream zake zitaganda mapema zaidi kabla ya wengine. Hivyo kulikuwa na changamoto mbili muhimu kwa Mpemba na wenzake, kupata nafasi ya kuweka ‘ice cream’ kwenye jokofu, na kuweka mapema zaidi.

Siku moja wakati Mpemba anachemsha maziwa ya ice-cream, mwenzake (mshindani wake kwenye biashara ya ice-cream) aliamua asichemshe maziwa yake ya kutengenezea ice-cream ili awahi nafasi anayoipenda kwenye jokofu kabla Mpemba hajaweka kwenye nafasi yake hiyo. Kwa akili zake za kitoto hakujali afya za walaji, bali cha muhimu kwake ilikuwa awahi nafasi ndani ya jokofu. Mpemba aliendelea kuchemsha maziwa yake, lakini kwa bahati nzuri au mbaya ikawa imebaki nafasi moja tu kwenye jokofu, hivyo naye kwa hofu ya kupoteza hiyo nafasi moja iliyobaki kwenye jokofu akaamua asisubiri mpaka maziwa yapoe ndipo ayaweke jokofuni bali akayewaka hivyo hivyo yakiwa ya moto bado. Japo alijua ni matumizi mabaya ya jokofu, lakini aliamua kufanya hivyo. Anasimuliwa mwenyewe kwenye “andiko” hilo.

Baada ya saa moja na nusu hivi, wakiwa kwenye mapumziko ya vipindi vya darasani, Mpemba na mwenzake waliamua kwenda kwenye jokofu kuangalia hali ya bidhaa zao na pia usalama wa jokofu. Zaidi Mpemba alikuwa na wasiwasi kwa vile aliweka maziwa ya moto kwenye jokofu, hivyo alitaka kwenda kuhakiki usalama wa jokofu. Walichokiona ndicho ambacho leo hii kinajulikana kama “Mpemba effect”, Maziwa ya Mpemba ambayo aliyaweka kwenye jokofu yakiwa ya moto yalishaganda na kuwa ‘ice-cream’, haliyakuwa maziwa ya yule mwenzake aliyeweka mwanzoni zaidi ‘Maziwa ya baridi bila ya kuyachemsha’, yakiwa bado yangali tepe tepe (hayajaganda kuwa ice-cream).

Hali hii ilipekea sintofahamu kubwa kati yao, kwani yule mwanafunzi mwenzake hakuamini kilichokuwa kinatukia bali alimshutumu Mpemba kwamba huenda amechanganya hizo ‘sahani maalum’ walizokuwa wanazitumia kuwekea ‘ice-cream’ zao, Yaani akimaanisha kuwa zile anazodai Mpemba ni ‘ice cream’ zake (zile zilizoganda) sio za kwake, maana haiwezekani kikawaida zigande kabla ya zile za mwenzie aliyeziweka mapema zaidi na zikiwa zenye ubaridi. Mpemba naye hakuafiki hilo, kwa maana alikuwa na yakini na alichokiona, hakueleza waliumaliza vipi ubishani wao lakini kwa dhahiri ni tukio ambalo lilifungua ukurasa mpya katika maisha yake.

Siku kadhaa baada ya tukio hilo, Mpemba akiwa darasani aliamua kumuuliza mwalimu wake wa kidato cha 3 wa somo la Fizikia juu ya alichokishuhudia, lakini majibu ya mwalimu huyu yalimfanya abadili mawazo kwa muda. Kiufupi majibu ya mwalimu huyo yalikuwa sawa na ya yule rafiki yake Mpemba kuwa “Mpemba, Umechanganya sahani za kuhifadhia za ice-cream, hilo jambo haliwezi kutokea.”

Baada ya kumaliza kidato cha nne pale shuleni Magamba, Mpemba alijiunga na kidato cha tano katika shule ya sekondari Mkwawa, Iringa (sasa ni tawi la chuo kikuu cha Dar es salaam, MUCE), akichukua masomo ya sayansi. Siku moja wakiwa katika somo la Fizikia wanasomeshwa mada ya Joto (heat) wakati mwalimu anaielezea “Newton’s law of cooling” (kanuni ya upoaji ya bwana Newton), Mpemba alimuuliza mwalimu wake wa somo hilo wa kidato cha tano swali lile lile ambalo aliliuliza akiwa kidato cha tatu, “kwanini maziwa ya moto yanaganda haraka zaidi kuliko maziwa ya baridi?”

Mpemba alijikuta akiuliza swali hilo kwa sababu maalum, kwa kifupi kanuni hiyo ya bwana mkubwa Newton inaelekeza kwamba, kitu chenye joto-ridi linalokaribiana au kuwa na tofauti ndogo na joto-ridi la mazingira yake basi kitapoa haraka zaidi kuliko kile chenye joto-ridi kubwa sana zaidi ya joto-ridi la mazingira yake. Hii ndiyo kusema kwa mujibu wa kanuni hii ya Newton, Maziwa ya baridi yalitakiwa yagande haraka kwenye jokofu kuliko maziwa ya moto. Jambo ambalo Mpemba aliona ni tofauti na kilichotokea kwenye ‘ice cream’ zake.

Swali lake hili kwa mara nyengine likaibua sintofahamu na mabishano kati ya Mpemba kwa upande mmoja na Mwalimu na wanafunzi wenzie kwa upande wa pili. Mwalimu akisistiza kuwa jambo hilo haliwezekani kisayansi huku Mpemba naye akijenga hoja kuwa japo hakuna hayo maelezo ya Kisayansi lakini yeye amelishuhudia hilo likitokea kwa macho yake mwenyewe, wanafunzi wenzie hawakumuamini kabisa.

Pamoja na ushuhuda wake kukataliwa na wanafunzi pamoja na mwalimu wake lakini bado Mpemba alisimamia alichokiona, yeye aliamini si kila matokeo yalipaswa kwenda sabamba na hali iliyozoeleka na alitaka wenzie wajipe nafasi ya kukubali matokeo mapya tofauti na yale waliyoyazoea. Mwalimu wake baada ya kuchoshwa na Udadisi wake aliamua kuufunga mjadala huo wa kitaaluma kwa kebehi kuwa “hiyo (ya maziwa ya moto kuganda mapema zaidi ya maziwa ya baridi kwenye jokofu) itakuwa ni ‘Fizikia ya Mpemba’ na sio Fizikia ya Ulimwengu”.
Baada ya hapo ikawa ndio utani tena, kila alichokikosea shuleni pale kiliitwa ‘Cha Mpemba’, kwa mfano kwenye hesabu za“Alogarithims” alipokosea basi, mwalimu wa somo hilo na hata wanafunzi wenzie wangelisema hizo (alizokosea) ni ‘hesabu za Mpemba’ na sio hesabu za Algorithms! Lakini Mpemba, hakukatishwa tamaa na hali hiyo.

Siku moja akiwa katika Maabara ya Baiolojia shuleni hapo, aliamua kurudia jaribio lake, lakini badala ya kutumia maziwa mara hii alitumia maji, alijaza kiasi cha maji ujazo sawa kwenye “bikari” (Bilauri ndogo maalum zitumikazo maabara) mbili, moja akaweka maji ya baridi na nyengine akaweka maji ya moto, kisha akaziweka bikari mbili zile kwenye jokofu kwa muda wa saa moja.

Alipokuja kuziangalia baada ya hiyo saa moja alikuta bikari iliyokuwa na maji ya moto tayari imeshaanza kufanya barafu nyingi sana, wakati ile iliyokuwa na maji ya baridi ingali na maji na barafu kidogo! Hii ilizidi kumpa uhakika wa ugunduzi wake, ugunduzi uliokataliwa na waalimu wake wawili wa somo la Fizikia pamoja na wanafunzi wenzie.

Wakati mmoja wanafunzi wa kidato cha tano na sita shuleni Mkwawa walipata nafasi ya kutembelewa na Mhadhiri mwandamimizi kutoka Chuo Kikuu cha Dar es Salaam, Dk. Denis Osborne (wakati huo akiwa bado ni Daktari wa falsafa tu, sasa Profesa Osborne) ambaye alikuwa ni mtaalamu wa Fizikia. Osborne alialikwa shuleni pale na Mkuu wa shule hiyo ili aje kuwahamasisha wanafunzi wa shule hiyo kusoma kwa bidii ili wafaulu na wafanikiwe kujiunga na masomo ya Chuo kikuu.

Lakini akiwa ni mtaalamu wa Fizikia alizungumza kidogo kuhusu somo hilo, mwishoni Wanafunzi walipewa nafasi ya kumuuliza Dk. Osborne maswali mbalimbali mara baada kumaliza mazungumzo yake. Maswali yalikuwa mengi, yapo yaliyohusu namna ya kujiunga na chuo kikuu, idadi ya wanaotakiwa kuingia chuo kikuu, ugumu na wa somo la Fizikia chuo kikuu, unakuwa nani ukimaliza Sahahada ya Fizikia?, n.k. Lakini swali lilowavunja mbavu kwa kicheko wanafunzi wengi kama si wote, hata kupelekea wengine kuona aibu, ni swali alilouliza Erasto Mpemba.

Mpemba alimuuliza Dk. Osborne swali lile lile alilowahi kuwauliza mwanzoni walimu wake wawili wa Fizikia, tofauti ikiwa mara hii akiuliza kuhusu maji na siyo maziwa, na akiwa makini zaidi kujua joto-ridi la awali la maji yake, alimuuliza “Inakuaje ukijaza maji ya moto yenye nyuzi joto 100 za sentigredi na maji baridi yenye nyuzi joto 35 za sentigredi, kwa ujazo sawa kwenye ‘beaker’ mbili tofauti kisha ukaweka kwenye jokofu, maji yaliyokuwa na nyuzi joto 100 za sentigredi yanaganda kabla ya yale yaliyokuwa na nyuzi joto 35 za sentigredi?”

Dk. Osborne, kwanza alicheka kama walivyocheka wengine katika hadhara ile, kisha akamwambia Mpemba arudie swali lake. Mpemba akarudia kile kile alichokiuliza mara ya kwanza, Mara hii uzingatiaji wa Dk. Osborne ulikuwa mkubwa zaidi, mara baada ya Mpemba kurudia swali lake akamuuliza “una hakika umefanya hivyo?”

Mpemba akajibu ndio, nna hakika nimefanya, hapa Prof. Osborne alionesha utofauti wa hali ya juu katika kuiendea kesi hii! Kwanza alitaka kujiridhisha kama kweli alichosikia ndicho kilichoulizwa, pili alitaka kujua imani ya muuliza swali juu ya anachokiuliza (uhakika wake), na tatu na muhimu sana katika taaluma yoyote, alitaka kujua chanzo cha hoja, ndo maana akamuuliza (je ni kweli umefanya wewe mwenyewe?). Baada ya kujiridhisha na yote hayo alijibu swali la Mpemba kwa kumwambia kuwa “Sijui kwa kweli, lakini nakuahidi kuwa nitajaribu huo uchunguzi nikifika Dar es Salaam”.

Kinachofurahisha zaidi kutoka kwa Dk. Osborne sio namna alivyolisikiliza swali kwa umakini mkubwa, bali ni ile hali ya kuwa tayari kusikia na kupokea kitu kipya kutoka hata kwa mwanafunzi wa sekondari ya Kijijini Mkwawa. Jiulize ni maDokta, maProfesa au Walimu vyuoni, mashuleni na kwenye vituo vyetu vya utafiti walio tayari kupokea wazo jipya (ambalo halijatoka kwa wanasyansi wa nje) kutoka kwa wanafunzi wao au hata wafanyakazi wenzao waliochini yao kielimu? Ni wachache sana!

Wanafunzi wenzake, hasa wale wanaojiita vipanga, hawakufurahishwa na kitendo chake cha kuuliza swali ambalo wao waliliona ni la kipuuzi, walifikia hatua hata ya kumhoji “Hivi Mpemba umeelewa kweli ‘sura nzima’ ya kitabu inayoelezea Newtons law of cooling?” Lakini Mpemba siku zote alipenda kuwajibu kuwa “Nadharia wakati mwengine hutofautiana na majibu ya uchuguzi kwa vitendo”.

Dk. Osborne aliporudi Dar es salaam aliurudia ule uchunguzi, kwa kuweka maji ya moto na baridi kwenye ‘bikari’ mbili tofauti (ujazo sawa kama Mpemba), kisha akaziweka bilauri zile kwenye jokofu kwa muda wa saa moja. Majibu aliyopata ni kama yale aliyoyapata Mpemba kule Magamba na hatimaye pale Iringa. Kwa kutumia ufahamu wake kwenye sayansi (Fizikia), alijaribu kuelezea, sababu zinazoweza kupelekea hali hiyo, na hatimaye mwaka 1969, walichapisha chapisho lao (scientific paper) kwenye Jarida la ‘Journal of Physics Education’ lenye kichwa cha habari (Title), “Cool?” (Poa?).

Chapisho hilo ni moja ya Maandiko machache ya Kisayansi ambayo yameandikwa katika mtindo wa Masimulizi. Ni simulizi ya kweli katika ulimwengu wa sayansi na ugunduzi, Simulizi inayobeba mambo mengi na inayoonesha uhalisia wa mfumo mbovu wa elimu yetu. Maana hata baada ya kumaliza kidato sita, Mpemba alipotea kabisa katika ulimwengu wa sayansi na aliishia kusoma “Chuo cha uhifadhi Wanyamapori” badala ya kuwa Mwanasayansi.

Ni simulizi inayoonyesha kuwa pamoja na ukatishwaji tamaa mkubwa unaofanywa kwa wanafunzi mashuleni lakini pia hakuna juhudi zozote zinazofanywa kuviendeleza vipaji mbalimbali vinachomozwa na kuushinda mtihani huo wa kukatishwa tamaa. Kutokana na masimulizi haya tunaonyeshwa kuwa “Udhani” hata kama umeasisiwa na wanasayansi wakubwa wa kimagharibi na Amerika, bado unaweza kuwa na mapungufu katika kulielezea jambo husika, hivyo bado kuna nafasi ya kuzifanyia marekebisho na hata kuzipinga tafiti mbalimbali zilizowahi kufanywa.
Pia simulizi hii imetuonesha tofauti ya kuwa na wasomi ambao ni “wadadisi” na wale ambao ni wasomi “wahafidhina” wanaoendesha taaluma zao kiimla na kimazoea. Zaidi ya yote hii ni simulizi inayotufunza kuwa “Hakuna swali la kipuuzi”.

Chakusikitisha zaidi, ambacho ndicho kilichonisukuma kuandika makala hii, ni jinsi utafiti huu wa kujivunia, na wa kipekee, uliofanywa na wataaalam wetu ndani ya ardhi yetu, hautajwi wala kusimuliwa popote nchini, si katika shule wala vyuo vyetu. Baadhi ya vyanzo vya Kitafiti duniani vimeainisha kwamba “Mpemba effect” ni moja kati ya ‘Falsafa chache za Kifizikia’ (kama sio pekee tu) iliyopewa jina la mtafiti wa kiafrika.

Ajabu, hapa Tanzania tumeshindwa hata kumweka Mpemba kwenye vitabu vya hadithi vya shule za Msingi ili watoto wetu wajifunze, wahamasike na waamini kwamba inawezekana kuwa mwanasayansi mgunduzi hata bila kufika Chuo Kikuu. Hilo lingefanyika lingewapa fursa wanafunzi hawa ya kujifunza kujiamini na kutokata tamaa juu ya kile wanachokiamini au kukijua. Zaidi wangejifunza mbinu za kuhimili changamoto, wangetambua kwamba katika kila hatua ya maendeleo viko vizingiti vya kukatisha tamaa, na hivyo wangejifunza namna ya kuenenda katika nyakati hizo.

Kwa kuona umuhimu mkubwa wa “Mpemba effect” katika ulimwengu huu wa Sayansi na Teknolojia, Mwaka 2012 tu, Jarida ya ‘The Royal Society of Chemistry’ la Chuo Kikuu cha Cambridge cha Uingereza, ambalo ni moja ya Majarida Makongwe sana na yenye hadhi ya juu ya Kitaaluma duniani lilitangaza zawadi nono ya pesa kwa mtu au kikundi cha wanasayansi watakaoweza kutoa maelezo mazuri, bora na ya kujenga zaidi kuhusu “dhana” kwamba maji ya moto yanaganda mapema zaidi kabla ya maji ya baridi - “Mpemba effect”.

Watu zaidi ya ishirini na mbili elfu (22,000) walijitokeza, Kisha 11 wakaingia fainali, na hatimaye Nikola Bregovic kutoka Croatia ambaye ni mfanyakazi wa Maabara ya Kemia katika Chuo Kikuu cha Zagreb, akatangazwa kuwa mshindi. Januari 10, 2013 Mtanzania Erasto Bartholomeo Mpemba ndiye aliyepewa heshima kubwa ya kumtangaza mshindi na kumpa zawadi hiyo kwa niaba ya Jaribu la ‘The Royal Society of Chemistry’, tukio ambalo lilichochea hamasa juu ya Udadisi, Utafiti na Ugunduzi kwa vijana wengi wa Ulaya.

“Mpemba effect” iko bado na inaishi kwenye maabara mbalimbali duniani, kuanzia Ulaya, Amerika na Asia, lakini sio Tanzania. Tafiti mbali mbali zimeshafanywa (Katz, 2009, Esposito, 2008, na Auerbach, 1995), na bado zinaendelea kufanywa ili kutafuta sababu za msingi za “dhana” hii ili mwishowe iweze kuwekwa katika matumizi sahihi kama kanuni (law) kwa ajili ya maendeleo ya wanaadam.

Pichani ni Erasto B Mpemba akiwa pamoja na Profesa Denis Osborne katika moja ya Mikutano mbalimbali waliyohudhuria pamoja duniani. Picha na Maelezo haya ni kwa hisani kubwa ya Ndugu Ally Mahadhy, Mwanafunzi wa Kitanzania wa Shahada ya Uzamivu katika Chuo Kikuu cha Lund, Sweden.View attachment 406080

Mpemba effect
From Wikipedia, the free encyclopedia
The Mpemba effect is a process in which hot water can freeze faster than cold water. The phenomenon is temperature-dependent. There is disagreement about the parameters required to produce the effect and about its theoretical basis.[1][2]



The Mpemba effect is named after Erasto Batholomeo Mpemba (b.1950) who discovered it in 1963. There are ancient accounts of similar phenomena, but the detail is insufficient to attempt verification.

Contents

• 1 Definition
• 2 Observations
  • 2.1 Historical context
  • 2.2 Mpemba's observation
  • 2.3 Modern context
• 3 Suggested explanations
• 4 Recent views
• 5 Similar effects
• 6 See also
• 7 References
• 8 Bibliography
• 9 External links

Definition
The phenomenon, when taken to mean "hot water freezes faster than cold", is difficult to reproduce or confirm because this statement is ill-defined.[3] Monwhea Jeng proposes as a more precise wording:

There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner.[4]

However, even with this definition it is not clear whether "freezing" refers to the point at which water forms a visible surface layer of ice; the point at which the entire volume of water becomes a solid block of ice; or when the water reaches 0 °C (32 °F).[3] A quantity of water can be at 0 °C (32 °F) and not be ice; after enough heat has been removed to reach 0 °C (32 °F) more heat must be removed before the water changes to solid state (ice), so water can be liquid or solid at 0 °C (32 °F).

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.[3] On the other hand, there may be many circumstances in which the effect is not observed.[3]

Observations
Historical context
Various effects of heat on the freezing of water were described by ancient scientists such as Aristotle: "The fact that the water has previously been warmed contributes to its freezing quickly: for so it cools sooner. 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."[5] Aristotle's explanation involved antiperistasis, "the supposed increase in the intensity of a quality as a result of being surrounded by its contrary quality."

Early modern scientists such as Francis Bacon noted that, "slightly tepid water freezes more easily than that which is utterly cold."[6] In the original Latin, "aqua parum tepida facilius conglacietur quam omnino frigida."

René Descartes wrote in his Discourse on the Method, "One can see by experience that water that has been kept on a fire for a long time freezes faster than other, the reason being that those of its particles that are least able to stop bending evaporate while the water is being heated."[7] This relates to Descartes' vortex theory.

The Scottish scientist Joseph Black investigated a special case of this phenomenon comparing previously-boiled with unboiled water;[8] the previously-boiled water froze more quickly. Evaporation was controlled for. He discussed the influence of stirring on the results of the experiment, noting that stirring the unboiled water led to it freezing at the same time as the previously-boiled water, and also noted that stirring the very-cold unboiled water led to immediate freezing. Joseph Black then discussed Fahrenheit's description of supercooling of water (although the term supercooling had not then been coined), arguing, in modern terms, that the previously-boiled water could not be as readily supercooled.

Mpemba's observation
The effect is named after Tanzanian Erasto Mpemba. He described it in 1963 in Form 3 of Magamba Secondary School, Tanganyika, when freezing ice cream mix that was hot in cookery classes and noticing that it froze before the cold mix. He later became a student at Mkwawa Secondary (formerly High) School in Iringa. The headmaster invited Dr. Denis G. Osborne from the University College in Dar es Salaam to give a lecture on physics. After the lecture, Erasto Mpemba asked him the question, "If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?", only to be ridiculed by his classmates and teacher. After initial consternation, Osborne experimented on the issue back at his workplace and confirmed Mpemba's finding. They published the results together in 1969, while Mpemba was studying at the College of African Wildlife Management.[9]

Modern context
Mpemba and Osborne describe placing 70 ml (2.5 imp fl oz; 2.4 US fl oz) samples of water in 100 ml (3.5 imp fl oz; 3.4 US fl oz) beakers in the ice box of a domestic refrigerator on a sheet of polystyrene foam. They showed the time for freezing to start was longest with an initial temperature of 25 °C (77 °F) and that it was much less at around 90 °C (194 °F). They ruled out loss of liquid volume by evaporation as a significant factor and the effect of dissolved air. In their setup most heat loss was found to be from the liquid surface.[9]

David Auerbach describes an effect that he observed in samples in glass beakers placed into a liquid cooling bath. In all cases the water supercooled, reaching a temperature of typically −6 to −18 °C (21 to 0 °F) before spontaneously freezing. Considerable random variation was observed in the time required for spontaneous freezing to start and in some cases this resulted in the water which started off hotter (partially) freezing first.[10]

James Brownridge, a radiation safety officer at the State University of New York, has said that he believes that supercooling is involved.[11] Several molecular dynamics simulations have also supported that changes in hydrogen bonding during supercooling takes a major role in the process.[12][13]

In 2016, Burridge and Linden defined the criterion as the time to reach 0 °C (32 °F), carried out experiments and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers. They say, "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect".[1]

However, in 2017, two research groups independently and simultaneously found theoretical evidence of the Mpemba effect and also predicted a new "inverse" Mpemba effect in which heating a cooled, far-from-equilibrium system takes less time than another system that is initially closer to equilibrium. Lu and Raz[14] yield a general criterion based on Markovian statistical mechanics, predicting the appearance of the inverse Mpemba effect in the Ising model and diffusion dynamics. Lasanta and co-workers[15]predict also the direct and inverse Mpemba effects for a granular gas in a far-from-equilibrium initial state. In this last work, it is suggested that a very generic mechanism leading to both Mpemba effects is due to a particle velocity distribution function that significantly deviates from the Maxwell-Boltzmann distribution.

Suggested explanations
The following explanations have been proposed:

• Evaporation: The evaporation of the warmer water reduces the mass of the water to be frozen.[16] Evaporation is endothermic, meaning that the water mass is cooled by vapor carrying away the heat, but this alone probably does not account for the entirety of the effect.[4]
• Convection: Accelerating heat transfers. Reduction of water density below 4 °C (39 °F) tends to suppress the convection currents that cool the lower part of the liquid mass; the lower density of hot water would reduce this effect, perhaps sustaining the more rapid initial cooling. Higher convection in the warmer water may also spread ice crystals around faster.[17]
• Frost: Has insulating effects. The lower temperature water will tend to freeze from the top, reducing further heat loss by radiation and air convection, while the warmer water will tend to freeze from the bottom and sides because of water convection. This is disputed as there are experiments that account for this factor.[4]
• Solutes: The effects of calcium carbonate, magnesium carbonate among others.[18]
• Thermal conductivity: The container of hotter liquid may melt through a layer of frost that is acting as an insulator under the container (frost is an insulator, as mentioned above), allowing the container to come into direct contact with a much colder lower layer that the frost formed on (ice, refrigeration coils, etc.) The container now rests on a much colder surface (or one better at removing heat, such as refrigeration coils) than the originally colder water, and so cools far faster from this point on.
• Dissolved gases: Cold water can contain more dissolved gases than hot water, which may somehow change the properties of the water with respect to convection currents, a proposition that has some experimental support but no theoretical explanation.[4]
• Hydrogen bonding: In warm water, hydrogen bonding is weaker.[2]
• Crystallization: Another explanation suggests that the relatively higher population of water hexamer states in warm water might be responsible for the faster crystallization.[12]
• Distribution function: Strong deviations from the Maxwell-Boltzmann distribution results in potential Mpemba effect showing up in gases[15].

Recent views
A reviewer for Physics World writes, "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." He pointed out that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.[3]

New Scientist recommends starting the experiment with containers at 35 and 5 °C (95 and 41 °F) to maximize the effect.[19] In a related study, it was found that freezer temperature also affects the probability of observing the Mpemba phenomenon as well as container temperature.

In 2012, the Royal Society of Chemistry held a competition calling for papers offering explanations to the Mpemba effect.[20] More than 22,000 people entered and Erasto Mpemba himself announced Nikola Bregović as the winner. Bregović suggests two reasons for the effect — a colder sample gets supercooled rather than frozen, and enhanced convection in the warmer sample speeds up cooling by maintaining the heat gradient on the container walls.[21]

Tao and co-workers proposed yet another possible explanation in 2016. On the basis of results from vibrational spectroscopy and modeling with density functional theory-optimized water clusters, they suggest that the reason might lie in the vast diversity and peculiar occurrence of different hydrogen bonds. Their key argument is that the number of strong hydrogen bonds increases as temperature is elevated. The existence of the small strongly-bonded clusters facilitates in turn the nucleation of hexagonal ice when warm water is rapidly cooled down.[2]

Similar effects
Other phenomena in which large effects may be achieved faster than small effects are

• Latent heat: turning 0 °C (32 °F) ice to 0 °C (32 °F) water takes the same amount of energy as heating water from 0 °C (32 °F) to 80 °C (176 °F)
• Leidenfrost effect: lower temperature boilers can sometimes vaporize water faster than higher temperature boilers

See also

• Water cluster
• Density of water

References
Notes

• Burridge, Henry C.; Linden, Paul F. (2016). "Questioning the Mpemba effect: Hot water does not cool more quickly than cold". Scientific Reports. 6: 37665. Bibcode:2016NatSR...637665B. doi:10.1038/srep37665. PMC 5121640 
  
  . PMID 27883034.

• Tao, Yunwen; Zou, Wenli; Jia, Junteng; Li, Wei; Cremer, Dieter (2017). "Different Ways of Hydrogen Bonding in Water - Why Does Warm Water Freeze Faster than Cold Water?". Journal of Chemical Theory and Computation. 13: 55. doi:10.1021/acs.jctc.6b00735.

• Ball, Philip (April 2006). Does hot water freeze first?. Physics World, pp. 19-26.

• Jeng, Monwhea (2006). "Hot water can freeze faster than cold?!?". American Journal of Physics. 74 (6): 514. arXiv:physics/0512262v1 
  
  . Bibcode:2006AmJPh..74..514J. doi:10.1119/1.2186331.

• Aristotle, Meteorology I.12 348b31–349a4

• Bacon, Francis; Novum Organumde, Lib. II, L

• Descartes, René; Les Météores

• Black, Joseph (1 January 1775). "The Supposed Effect of Boiling upon Water, in Disposing It to Freeze More Readily, Ascertained by Experiments. By Joseph Black, M. D. Professor of Chemistry at Edinburgh, in a Letter to Sir John Pringle, Bart. P. R. S.". Philosophical Transactions of the Royal Society of London. 65: 124–128. doi:10.1098/rstl.1775.0014.

• Mpemba, Erasto B.; Osborne, Denis G. (1969). "Cool?". Physics Education. Institute of Physics. 4 (3): 172–175. Bibcode:1969PhyEd...4..172M. doi:10.1088/0031-9120/4/3/312. republished as Mpemba,, Erasto B.; Osborne, Denis G. (1979). "The Mpemba effect" (PDF). Physics Education. Institute of Physics. 14 (7): 410–412. Bibcode:1979PhyEd..14..410M. doi:10.1088/0031-9120/14/7/312.

• Auerbach, David (1995). "Supercooling and the Mpemba effect: when hot water freezes quicker than cold" (PDF). American Journal of Physics. 63 (10): 882–885. Bibcode:1995AmJPh..63..882A. doi:10.1119/1.18059.

• Chown, Marcus (24 March 2010). "Revealed: why hot water freezes faster than cold". New Scientist.

• Jin, Jaehyeok; Goddard III, William A. (2015). "Mechanisms Underlying the Mpemba Effect in Water from Molecular Dynamics Simulations". Journal of Physical Chemistry C. 119 (5): 2622–2629. doi:10.1021/jp511752n.

• Xi, Zhang; Huang, Yongli; Ma, Zengsheng; Zhou, Yichun; Zhou, Ji; Zheng, Weitao; Jiange, Qing; Sun, Chang Q. (2014). "Hydrogen-bond memory and water-skin supersolidity resolving the Mpemba paradox". Physical Chemistry Chemical Physics. 16 (42): 22995–23002. arXiv:1310.6514 
  
  . Bibcode:2014PCCP...1622995Z. doi:10.1039/C4CP03669G.

• Lu, Zhiyue; Raz, Oren (2017-05-16). "Nonequilibrium thermodynamics of the Markovian Mpemba effect and its inverse". Proceedings of the National Academy of Sciences. 114 (20): 5083–5088. arXiv:1609.05271 
  
  . Bibcode:2017PNAS..114.5083L. doi:10.1073/pnas.1701264114. ISSN 0027-8424. PMC 5441807 
  
  . PMID 28461467.

• Lasanta, Antonio; Vega Reyes, Francisco; Prados, Antonio; Santos, Andrés (2017). "When the Hotter Cools More Quickly: Mpemba Effect in Granular Fluids". Physical Review Letters. 119 (14): 148001. arXiv:1611.04948 
  
  . Bibcode:2017PhRvL.119n8001L. doi:10.1103/physrevlett.119.148001.

• Kell, George S. (1969). "The freezing of hot and cold water". American Journal of Physics. 37 (5): 564–565. Bibcode:1969AmJPh..37..564K. doi:10.1119/1.1975687.

• CITV Prove It! Series 1 Programme 13

• Katz, Jonathan (April 2006). "When hot water freezes before cold". American Journal of Physics. 77 (27): 27. arXiv:physics/0604224 
  
  . Bibcode:2009AmJPh..77...27K. doi:10.1119/1.2996187.

• How to Fossilize Your Hamster: And Other Amazing Experiments for the Armchair Scientist, ISBN 1-84668-044-1

• Mpemba Competition, Royal Society of Chemistry, 2012

1. Bregović, Nikola; Mpemba effect from a viewpoint of an experimental physical chemist, 2013

Bibliography

• Auerbach, David (1995). "Supercooling and the Mpemba effect: when hot water freezes quicker than cold" (PDF). American Journal of Physics. 63 (10): 882–885. Bibcode:1995AmJPh..63..882A. doi:10.1119/1.18059.
  • Auerbach attributes the Mpemba effect to differences in the behaviour of supercooled formerly hot water and formerly cold water.
• Chown, Marcus (June 2006). "Why water freezes faster after heating". New Scientist.
• Conover, Emily (2017). "Debate heats up over claims that hot water sometimes freezes faster than cold". Science News. 191 (2): 14. Retrieved 2 April 2018.
• Dorsey, N. Ernest (1948). "The freezing of supercooled water". Trans. Am. Phil. Soc. American Philosophical Society. 38 (3): 247–326. doi:10.2307/1005602. JSTOR 1005602.
  • An extensive study of freezing experiments.
• Jeng, Monwhea (2006). "The Mpemba effect: When can hot water freeze faster than cold?". American Journal of Physics. 74 (6): 514. arXiv:physics/0512262 
  
  . Bibcode:2006AmJPh..74..514J. doi:10.1119/1.2186331.
• Knight, Charles A. (May 1996). "The MPEMBA effect: The freezing times of hot and cold water". American Journal of Physics. 64 (5): 524. Bibcode:1996AmJPh..64..524K. doi:10.1119/1.18275.

External links

Wikimedia Commons has media related to Mpemba effect.

• Mpemba Competition - Royal Society of Chemistry
• Mpemba, Erasto B.; Osborne, Denis G. "The Mpemba effect" (PDF). Institute of Physics.
• Adams, Cecil; M. Q. C., Mary (1996). "Which freezes faster, hot water or cold water?". The Straight Dope. Chicago Reader, Inc.
• Brownridge, James (2010). "A search for the Mpemba effect: When hot water freezes faster than cold water". arXiv:1003.3185 
  
  [physics.pop-ph].
• "Heat questions". HyperPhysics. Georgia State University.
• "The Mpemba Effect". Archived from the original on 9 October 2011. - History and analysis of the Mpemba Effect.
• Jeng, Monwhea (November 1998). "Can hot water freeze faster than cold water?". in the University of California Usenet Physics FAQ
• "The Phase Anomalies of Water: Hot Water may Freeze Faster than Cold Water". An analysis of the Mpemba effect. London South Bank University.
• "Mpemba effect: Why hot water can freeze faster than cold". A possible explanation of the Mpemba Effect
• "The story of the Mpemba effect told by the protagonists". An historical interview with Erasto B. Mpemba, Dr Denis G. Osborne and Ray deSouza
• Sun, Chang Q.; Sun, Yi (2016). "The Attribute of Water: Single Notion, Multiple Myths". Springer Series in Chemical Physics.

Source: Mpemba effect - Wikipedia

 

[Ilankunda1234]

Sidhani km huyu jamaa anajulikana au hiyo effect ishawahi hata kufundishwa uko vyuoni au shuleni! Nilisoma PCM na sikuwahi kuambiwa au kusoma sehemu kuhusu "mpemba effect" hii kitu ifanyiwe kazi tafadhali! Atangazwe kwa mbwembwe zote

Baadhi ya nchi wanaitumia hii kimya kimya kusafirishia maji machafu hasa zile za baridi ambazo hapo awali walikuwa wanachemsha kwanza