Stay hun­gry,

Finweek English Edition - - MANAGEMENT -

Iwant you to imag­ine an ex­per­i­ment. We start with two glasses of wa­ter, which are iden­ti­cal to each other in all re­spects, ex­cept one. The only dif­fer­ence be­tween the two is that the wa­ter in one glass is hot while the wa­ter in the other glass is cold. Now we cool both glasses, us­ing the ex­act same cool­ing process, un­til the wa­ter freezes. The ques­tion is, which one will freeze first?

Well, ob­vi­ously it ’s the cold wa­ter, right? Let’s say it takes 10 min­utes for the cold wa­ter to freeze. Then the hot wa­ter is go­ing to take some time to cool down to the tem­per­a­ture of the cold wa­ter, and then it’s go­ing to take an­other 10 min­utes. So the hot wa­ter has to do ev­ery­thing the cold wa­ter does, plus a lit­tle more, which means that it has to take longer.

It seems to be a sim­ple so­lu­tion, and you’d be right – most of the time. But not al­ways.

THE STORY OF ERASTO MPEMBA

In 1963, a young Tanzanian high school stu­dent named Erasto Mpemba was mak­ing ice cream at school in the cook­ery class. The in­struc­tions were to mix boil­ing milk with sugar, wait for it to cool, and then place the mix­ture into a freezer. As more and more of his fel­low pupils fin­ished the task, Erasto saw the valu­able freezer space be­ing used up quickly. So he took a short-cut – in­stead of wait­ing for his mix­ture to cool down, he put his milk in while it was still hot. Some­time later, he opened the freezer to dis­cover some­thing very sur­pris­ing. For some strange rea­son, his mix­ture had frozen into ice cream be­fore those of the other pupils. This seemed im­pos­si­ble, so he asked his physics teacher for an ex­pla­na­tion. The teacher dis­missed the ques­tion, say­ing that Erasto must have been con­fused.

Later that year, Mpemba was chat­ting with a friend of his who made and sold ice cream in the nearby town. His friend

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