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View Full Version : Power, speed and drag - the physics of Usain Bolt's world record


Judo
29th July 2013, 01:24 PM
Scientists model 'extraordinary' performance of Bolt (http://phys.org/news/2013-07-scientists-extraordinary.html)

The 2 bits I find most amazing are:


terminal velocity of 12.2 metres per second


Bolt developed 81.58 kJ of energy during the 9.58 seconds, but only 7.79% of this was used to achieve motion; the remaining 92.21% (75.22 kJ) was absorbed by the drag.
Hay Ewe
29th July 2013, 02:27 PM
yep,

the faster you go, the more the effect of drag.
double the speed, 4 times the drag

Hay Ewe
Dougal
29th July 2013, 02:40 PM
His drag coefficient of 1.2 is terrible. A defender has a drag coefficient of about half that.:o
clive22
29th July 2013, 02:50 PM
Sometime the numbers and relationships are illuminating.

Though most people who have ridden a pushbike into a stiff (head) wind would understand.

Remember too, to double the speed and overcome twice the drag you need to do the work twice as fast, so eight times, i.e. power = speed cubed.
So even knocking 1 sec off the ~10 sec 100m time time takes just over 33% more power from your muscles, that wont happen in a high level competition.

No wonder the records drop by such small amounts, 0.02 sec or so but that is significant ~6% more power over a 100m dash.

This ignores everything but wind resistance which is most of the work.

Clive
Judo
29th July 2013, 03:30 PM
It certainly becomes obvious why the choice of tight clothing is key!
isuzurover
29th July 2013, 03:41 PM
His drag coefficient of 1.2 is terrible. A defender has a drag coefficient of about half that.:o

Indeed. However the maths in the paper are a bit basic...

We were just discussing this here. Even an elephant is Cd~0.7
Judo
29th July 2013, 05:14 PM
Indeed. However the maths in the paper are a bit basic...

We were just discussing this here. Even an elephant is Cd~0.7
According to my text book on drag...

Drag coefficient - Wikipedia, the free encyclopedia

...on average a skier is 1.0. An upright person 1.15 and at 1.6 Usain is somewhere between the Empire State Building and the Eiffel Tower. I knew he was tall, but he's not that tall! :D
isuzurover
29th July 2013, 05:31 PM
According to my text book on drag...

Drag coefficient - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Drag_coefficient)

...on average a skier is 1.0. An upright person 1.15 and at 1.6 Usain is somewhere between the Empire State Building and the Eiffel Tower. I knew he was tall, but he's not that tall! :D

1.2, not 1.6
Judo
29th July 2013, 06:03 PM
Cancel. :angel: