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# Usain Bolt’s speed explained by scientists

## Usain Bolt’s extraordinary speed has been explained by scientists with a mathematical model.

Usain Bolt’s 100 m time of 9.58 seconds during the 2009 World Championships in Berlin is the current world record.

The scientists say their model explains the power and energy he had to expend to overcome drag caused by air resistance, made stronger by his frame of 6ft 5in.

Writing in the European Journal of Physics, the scientists hope to discover what makes extraordinary athletes so fast.

According to the mathematical model proposed, Usain Bolt’s time of 9.58 seconds in Berlin was achieved by reaching a speed of 12.2 metres per second, equivalent to about 27 mph.

The team calculated that Usain Bolt’s maximum power occurred when he was less than one second into the race and was only at half his maximum speed. This demonstrates the near immediate effect of drag, which is where air resistance slows moving objects.

They also discovered less than 8% of the energy his muscles produced was used for motion, with the rest absorbed by drag.

Usain Bolt’s extraordinary speed has been explained by scientists with a mathematical model

When comparing Usain Bolt’s body mass, the altitude of the track and the air temperature, they found out that his drag coefficient – which is a measure of the drag per unit area of mass – was actually less aerodynamic than that of the average man.

Jorge Hernandez of the National Autonomous University of Mexico said: “Our calculated drag coefficient highlights the outstanding ability of Bolt. He has been able to break several records despite not being as aerodynamic as a human can be.

“The enormous amount of work that Bolt developed in 2009, and the amount that was absorbed by drag, is truly extraordinary.

“It is so hard to break records nowadays, even by hundredths of a second, as the runners must act very powerfully against a tremendous force which increases massively with each bit of additional speed they are able to develop.

“This is all because of the ‘physical barrier’ imposed by the conditions on Earth. Of course, if Bolt were to run on a planet with a much less dense atmosphere, he could achieve records of fantastic proportions.

“The accurate recording of Bolt’s position and speed during the race provided a splendid opportunity for us to study the effects of drag on a sprinter.”

“If more data become available in the future, it would be interesting to see what distinguishes one athlete from another,” added Jorge Hernandez.

Usain Bolt’s time in Berlin was the biggest increase in the record since electronic timing was introduced in 1968.

John Barrow at Cambridge University who has previously analyzed how Usain Bolt could become even faster, explained that his speed came in part due his “extraordinary large stride length”, despite having such an initial slow reaction time to the starting gun.

“He has lots of fast twitch muscle fibres that can respond quickly, coupled with his fast stride is what gives him such an extraordinary fast time.”

John Barrow said Usain Bolt has lots of scope to break his record if he responded faster at the start, ran with a slightly stronger tail-wind and at a higher altitude, where there was less drag.

Usain Bolt’s Berlin record was won with a tail wind of only 0.9 m per second, which didn’t give him “the advantage of helpful wind assistance”, John Barrow added.

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# How to stay dry in the rain: run or walk?

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## Physicist Franco Bocci has put forth new ideas in the long-running question of how best to keep dry when moving in the rain.

If you run, you are out in the rain for less time, yet you run into more drops – so what is the optimal speed?

Franco Bocci, reporting in the European Journal of Physics, now asserts that both wind direction and a person’s stature figure into the answer.

In most cases, the general answer is to run as fast as possible; but the answer changes in a tailwind, or for the thin.

Prof. Franco Bocci is by no means the first person to address the problem, which is far more mathematically complex than it seems on the surface.

Physicist Franco Bocci has put forth new ideas in the long-running question of how best to keep dry when moving in the rain

In the 1970s, a number of papers came out in mathematics magazines debating the question, each more fully exploring the issues at hand.

The battleground for this bit of hobby mathematics now seems to be the UK’s Institute of Physics publication the European Journal of Physics.

In 1987, another Italian researcher asserted in the journal that changing strategies did not make a substantial difference.

In 2011, a textile expert and a physicist used the same publication to suggest that an optimal speed existed, depending on the wind direction.

“For the most part in the previous work, there was a simple answer, but I found that the problem is much more complicated,” said Prof. Franco Bocci.

What complicates the question is the human shape; for simplicity, previous attempts to crack the thorny problem assumed people to be thin sheets or upright, rectangular boxes.

When Prof. Franco Bocci considered a more general case – likely to be the case you would face in the rain – he found that the answer may depend on an individual’s height-to-breadth ratio as well as wind direction and raindrop size.

Luckily there are a few generalizations in the analysis, to spare you having to calculate the cosine of the angle between your path and the wind direction.

“Let’s say that in general, the best thing is to run, as fast as you can – not always, but in general,” said Prof. Franco Bocci.

“If you’re really thin, it’s more probable that there will be an optimal speed. Otherwise, it’s better to run fast.”

As for wind direction – and again, in general – you should run as fast as you can unless the wind is behind you, in which case the optimal speed will be exactly the speed of the wind.

Prof. Franco Bocci said that the problem promises to get even more complicated as more factors are taken into account, but that for now he is drying his hands of the question.