Wednesday, November 11, 2009

The Physics of Usain Bolt

I'm a sucker for these type of analysis and article. It is a lot of fun to read when it isn't really connected to "significant" physics research, mainly because for me, it is a pleasant diversion from my work, but still intellectually stimulating. Furthermore, exercise like this can be something fun for a class or a group of students to do, because it is something they have seen or heard about, and it is based on really basic physics that they can do or follow along.

This is a preprint of a paper that will appear in AJP. It analyzes the mechanics of Usain Bolt's 100m sprints, both from the last Beijing Olympics in 2008, and the recent Track and Field Championship in 2009, both resulting in new world records.

Abstract: At the 2008 Summer Olympics in Beijing, Jamaican athlete Usain Bolt broke the world record for the 100 m sprint. Just one year later, at the 2009 World Championships in Athletics in Berlin he broke it again. A few months after Beijing, Eriksen et al. studied Usain Bolt's performance and predicted that the record could be about one-tenth of second faster, which was confirmed in Berlin. In this paper we extend the analysis of Ref. [1] to model Bolt's velocity profile for the Beijing 2008 and Berlin 2009 records. From the results we obtained, we were able to deduce the maximum force, the maximum power and the total mechanical energy produced by the athlete in both races. Surprisingly, we concluded that all of these values were smaller in 2009 than in 2008.

Oooh.. now that last part is, indeed, surprising. You have to read it to find out why! :)

Edit: this has now appeared in AJP. The exact citation is:

O. Helene and M.T. Yamashita, Am. J. Phys. v.78, p.307 (2010).



Klaus said...

My friend Christoph Schiller told me that he writes in the last edition of his free Motion Mountain physics text that Usain Bolt is such a fast sprinter because he has a straight spine. What usually is a disadvantage in life becomes an advantage for sprinters, as this affliction, which he shares with Michael Johnson, allows to run faster than people with healthy, curved spines.

Kent Leung said...

Interesting theory. According to Michael "straight-spine" Johnson, typically tall runners don't do so well in the 100m races because they lack the coordination which is crucial during the powerful initial acceleration required in the 100m race. Of course, long legs are devastating over longer distances. Usain Bolt is so amazing because he is tall but still very coordinated. He is a true prodigy and will certainly revolutise traditional ideas about the 100m race. Not bad for a man who professes to love eating KFC.

It would be interesting to test this theory with similar analysis as in the paper but looking at the correlation between peak power and sprinter height for many sprinters.

Btw, it's not suprising the peak power in Beijing was better than in Berlin. Athletes design their schedule over a period of 2 years (or more) to peak for the olympics. The emotional response of when he realised he had won that race showed how much it meant to him. He must have been super focused and hyper-charged with adrenaline for it, must more so than for Berlin I think.

joel said...

Here is a presentation of a mathematical derivation of Usain Bolt's power I developed. It uses a different method than the quoted article and assumes constant power. It arrives at a value of : 2100 watts or about 3 horsepower.

Joel Harband