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

  1. 29th July 2013, 02:24 PM #1
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    Power, speed and drag - the physics of Usain Bolt's world record

    Scientists model 'extraordinary' performance of Bolt

    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.
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  2. 29th July 2013, 03:27 PM #2
    Hay Ewe
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    yep,

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

    Hay Ewe
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  3. 29th July 2013, 03:40 PM #3
    Dougal
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    His drag coefficient of 1.2 is terrible. A defender has a drag coefficient of about half that.
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  4. 29th July 2013, 03:50 PM #4
    clive22
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    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
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  5. 29th July 2013, 04:30 PM #5
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    It certainly becomes obvious why the choice of tight clothing is key!
    - Justin

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  6. 29th July 2013, 04:41 PM #6
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    Quote Originally Posted by Dougal View Post
    His drag coefficient of 1.2 is terrible. A defender has a drag coefficient of about half that.
    Indeed. However the maths in the paper are a bit basic...

    We were just discussing this here. Even an elephant is Cd~0.7
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  7. 29th July 2013, 06:14 PM #7
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    Quote Originally Posted by isuzurover View Post
    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...

    [ame="http://en.wikipedia.org/wiki/Drag_coefficient"]Drag coefficient - Wikipedia, the free encyclopedia[/ame]

    ...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!
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  8. 29th July 2013, 06:31 PM #8
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    Quote Originally Posted by Judo View Post

    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!
    1.2, not 1.6
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  9. 29th July 2013, 07:03 PM #9
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    Cancel.
    - Justin

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