A translation of an article about my work in Spanish Magazine ’Quo’. You can read the original article (in Spanish) here.

#### The naked math teacher fills the Madrid Student Residence

32 tattoos. One of them, the pokeball; platonic solids; his favourite equation (Navier-Strokes); the number e … And so, up to 32 tattoos are scattered around the body of Tom Crawford (@tomrockmaths) professor of mathematics at the University of Oxford. He arrived in Madrid invited by the Institute of Mathematical Sciences (ICMAT) for his Mathematics at the Residence cycle.

Undressing is something that Crawford defends to lighten the leaden role that mattes still have. So he often strips naked in his presentations and on his YouTube channel, from which he invites us all to do it to spread science.

In some of his videos, such as those in the *Equations Stripped* series, he explains the famous equations that he likes so much, those of Navier-Stokes, at the same time as he takes off layers of clothing.

In addition, the title of his conference in Madrid has another hook: Mathematics in sport. Soccer First: it promises to demonstrate how to shoot the perfect penalty. Then, elite running: it will discuss why the “zapamuelle” with which Eliud Kigchoge has just knocked down the two-hour wall running a marathon represent a performance advantage in the race of 4%.

So, despite the fact that it is pouring rain in Madrid, there is not a free seat in the Student Residence. There are many more young people among the public than usually attend science outreach talks. Most are students. The exchange of the cap for the piercing works.

The talk begins with the demonstration of the perfect penalty. Crawford explains that if Spain lost the 2018 World Cup in the penalty shootout, it was because mathematics was not used well. “He was chosen to shoot penalties at Koke, one of the players with the worst percentage of successes in the penalty shootouts of the National Team.” And Koke failed. The math would have left him on the bench before the extension.

The perfect penalty: 1.7 meters high and 0.65 meters from the inside of the post

After studying the speed of the shot on goal and the ability of the professional goalkeepers, Crawford concludes that the goalkeeper has half a second to react and move from when the player shoots. In that time he can move in an arc that does not occupy the entire goal and leaves four key points free. That’s where you have to hit the target. That is the perfect penalty shot: 1.7 meters high and 0.65 meters measuring from the stick towards the inside. Sure, you have to be right.

After the demonstration, Tom Crawford pulls out a toy goal and asks volunteers to rehearse their best shot. In the back of the conference room there is a row of launchers that give everything in one shot to the net. And the talk continues. Now, on the shoes of the Kenyan marathon runner for which 200 scientists have worked with the aim of overcoming one of those limits that separate the human from the superhuman.

Eliud Kipchoge dropped from two hours in the more than 42 km of the Marathon distance. He did it thanks to the help (among other things) of some sneakers, a prototype (they do not yet exist) that favour the race. Crawford used his maths to guess the future, and according to the data, he concludes that by the year 2032, going down those two inhumane hours will be a piece of cake among elite *runners*.

And so, while outside the residence the winter of Madrid did not skimp on the cold, inside the room that warmth produced by good conferences was accommodating.

Little else did the math teacher offer. He did not come to show great discoveries or explain the findings of his research, he came to the Student Residence to disclose in an environment that was always open to innovate.

Ah! And not. Crawford, this time he didn’t undress.