# Boffins calculate true speed of 'Lightning' Bolt

## 100m in 9.55 secs?

Physicists at the Institute of Theoretical Astrophysics at the University of Oslo have applied themselves to that most pressing of matters - how fast might Usain Bolt have run the 100m at the Beijing Olympics if he hadn't already been celebrating as he crossed the finishing line?

As history records, "Lightning" Bolt broke the world record with 9.69 seconds, but spent the last 20 metres beating his chest in joy, thereby slowing slighty in his thunderous progress down the track. Now, New Scientist explains, Hans Eriksen and colleagues have submitted to the American Journal of Physics a theoretical figure of 9.55 seconds.

To arrive at this new record, the team studied TV footage to "measure Bolt's positions, speeds and accelerations as well as those of the runner-up, Richard Thompson". Their measurements showed both Bolt and Thompson decelerating in the final couple of seconds of the race, "with a larger drop in speed for Bolt".

They then "calculated what Bolt's time would have been had he only slowed down as much as Thompson, arriving at an answer of 9.61 seconds".

Dissatisfied with this time, the boffins then - "somewhat arbitrarily", as NS puts it - decided that Bolt "would have decelerated less than Thompson, by 0.5 metres per second squared in the final two seconds", leading to a healthier 9.55 seconds.

Eriksen said: "We don't mean to say that this is the final and ultimate result. Instead, it's a fun application of simple physics, and we've done the best we can."

It's just as well the Oslo researchers aren't claiming a definitive result, because human locomotion expert Matthew Bundle, of the University of Wyoming in Laramie, clarified that it's "difficult to get precise measurements from ordinary TV footage, which records at 30 frames per second or less".

More precise calculations would require footage at 125 to 250 frames per second, "or on tracking motion with a series of light beams which get tripped as people go by", Bundle said, although he did concede the team's results are "reasonable". ®

### Bootnote

If Oslo uni's Institute of Theoretical Astrophysics has any more time on its hands, it might like to ponder this poser: What's the velocity of a Lightning Bolt in a vacuum?

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