Transcript:

Okay, question. You have a cup of hot water, and you have a cup of cold water or room temperature water. You put it in the freezer. Which do you think is going to freeze quicker?

You think that the cold water will become ice faster than the warm water, but no, it's not so obvious. There are instances in which the hot water freezes faster than the cold water. Yeah, this actually has a name. It's called the Mpemba effect. I don't know how to say the name, but this was a person in Tanzania in 1960. Their school was doing a project where all the kids in the classroom had to make ice cream.

And so they boiled milk, and they added sugar, etc., in it. And there were not enough ice trays to go around. So the kids were just waiting for the mixtures to cool down before they put them in the freezer.

And Mpemba took a shortcut: the hot mixture, he put it in the ice tray and put it in the freezer. And when the trays were removed, his ice cream was perfectly set, and the others' was not.

And this effect was explained many years later in 2012. Here's the link to the explanation. And it is a real effect.

So sometimes things are not obvious.