Jacob Mencke at one of Team Danmark’s ball machines.  Photographer: Andreas Top Adler, performance engineer, Team Danmark

Second-year student behind article in scientific journal

Monday 26 Oct 20

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Mirko Salewski
Associate Professor
DTU Physics
+45 23 66 84 44

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A special course on spinning balls, a technique which is used in many sports, sparked a string of experiments and calculations which have just been published in the American Journal of Physics.

Jacob Mencke plays football, and as a goalkeeper he has often wondered how to kick the ball in the best possible way with backspin in order to get it quickly up to the forwards at the other end of the pitch. Attending a three-week course in sports physics last summer therefore made obvious sense. Here, he studied the aerodynamics of spinning balls, and the trajectory they take through the air.

However, after the short course, Jacob did not feel that he had got to the bottom of things. He therefore asked his lecturer Mirko Salewski, Associate Professor at DTU Physics, to design a special course where he could immerse himself further and explore new areas such as the dynamics of when a spinning ball hits the ground and bounces back up again. This is a phenomenon which is not only relevant in football, but in most other ball sports as well.

Banana shots and ball machine

Jacob has conducted numerous experiments during the special course. These have involved asking his football teammates to perform banana shots, in which the ball curls and can head off in another direction after hitting the ground. All the shots were videoed and subsequently analysed. 

Another part of the data base was obtained with Team Danmark, with whom DTU regularly cooperates. Here, one of the ball machines which is used to train Denmark’s best handball goalkeepers and volleyball players was taken into use, where it is possible to set the level of spin on a thrown ball. Based on this data, Jacob was able to prepare a very accurate description of how balls pass through the air depending on the spin, and compared this with existing models of the complex fluid dynamic effects which determine a ball’s trajectory.  

Sport to spark an interest in physics

Based on data from experiments and calculations, Jacob described in an article how other students can easily conduct scientific experiments with aerodynamics without incurring significant costs, and afterwards model them using equations and numerical solutions. The idea is that this could happen, for example, in upper secondary school physics classes or in the first years at university.

“With a ball and a mobile phone that can record in slow motion, it’s possible to conduct the same type of experiments that I’ve done. In the article, I’ve published the codes which one can subsequently use in MATLAB or the free programming software Python to carry out calculations of the balls’ trajectories through the air while comparing it to the underlying theory,” says Jacob.

By taking the world of sport as his starting point, an area in which many young people are interested, he’s hoping to bring physics to a wider audience.   

Students seldom publish scientific articles

Mirko Salewski has never previously come across a university student doing work in his second year which can subsequently be published as a scientific article. 

“It’ll make some of our young researchers slightly envious, because it usually takes more than a year once you’ve graduated before you succeed in having anything published,” says Mirko Salewski. 

He underlines the fact that all the experiments and calculations were carried out by Jacob, but that he and the other supervisors have, of course, passed on what they know about writing scientific articles.

Jacob is continuing to study for his MSc in physics and nanotechnology, but does not yet know what he will use his education for at the end of the day. 
“Perhaps I’ll develop new sports equipment, such as designing the best football boots. On the other hand, I also find the idea of research quite appealing, so nothing is set in stone right now,” says Jacob.

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