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Thread: Captain Cook Fountain, Canberra, AU discussion

  1. #1
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    Default Captain Cook Fountain, Canberra, AU discussion

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    Captain Cook Fountain, Canberra, AU

    Not a whale in the middle of the lake. None of it is natural (the lake or the spray). Actually the Captain Cook Fountain welcoming people to Canberra, the capital of Australia. And given the right wind conditions the spray can completely wash your car on the bridge!


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    Lets go through this logically. The fountain sprays water a little over 100m in the air, the bridge which at its closest point is 218m away from the fountain is a little above water level. So let's assume the water has 100m to fall while travelling 218m sideways in order for it to actually hit your car.

    Now here are some simple high school physics formulas:

    (final velocity)^2 = (initial velocity)^2 * 2 * acceleration * distance

    This tells us that the final velocity of the water after falling 100m will be about 44m/s.

    And another:

    (final velocity) = (initial velocity) + (acceleration * time)

    Which tells us that the time taken for the water to reach this velocity (and therefore fall this distance) is about 4.5s. Let's be really generous and assume some air resistance on the water and say it takes 10s to fall this distance instead of 4.5s.

    So, the water has to travel 218m in 10s. That's equivalent to 21.8m/s, or about 78.5km/h and don't forget that I was been really generous on the time taken for it to fall so in all reality the water has to have a sideways velocity of much more than this (probably > 100km/h) in order for it to fall on the bridge.

    To get it moving that speed over that distance and time, the wind would have to be going a LOT faster than that.

    Canberra is not subject to constant wind speeds of > 100km/h, perhaps the occasional gust in a REALLY BAD storm but not often and certianly not constantly.

    It is highly unlikely that the water will hit the road and wash your car. Also I've lived in Canberra all my life and have never heard of it happening anyway. I'm pretty sure they would have taken this into account as well when actually deciding on the placement for the fountain.

  3. #3

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    Your application of simple high school physics formulas is very good except for this bit.

    Quote Originally Posted by dellamorte

    Let's be really generous and assume some air resistance on the water and say it takes 10s to fall this distance instead of 4.5s.
    Water at the top of the fountain would be in the form of droplets and rather then being subject to air resistance i would say it actually becomes part of the air and would be free to go with the wind at any speed for any distance.

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    Default Sure

    I do agree with you on this point and indeed when crossing the bridge you sometimes feel a mist. But a constant stream of water strong enough to clean your car which is going 70km/h over the bridge - that doesn't happen and that was my original point.

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