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    Re: Need dip-throw a rock?
    From: Gary LaPook
    Date: 2011 Jun 22, 17:29 -0700
    I thought that I was the only one who played petanque.

    gl

    --- On Wed, 6/22/11, Bill Morris <engineer{at}clear.net.nz> wrote:

    From: Bill Morris <engineer{at}clear.net.nz>
    Subject: [NavList] Re: Need dip-throw a rock?
    To: NavList@fer3.com
    Date: Wednesday, June 22, 2011, 3:58 PM

    I thought I would discover how well the rock-throwing method might work for me in practice. To avoid discussion about the behaviour of feathers and the shape of rocks, I used petanque balls. These are polished steel balls of 72 mm diameter and weighing 500 grammes, used in the game of petanque (q.v.).

    I threw them horizontally from the bridge of our ship "Baradozic" ("Little Paradise" in the Breton language - my wife is from Brittany)and used a stop watch reading to 0.01 second to time their fall onto level ground a measured 5.8 metres below.

    The mean time of 25 throws was 1.29 seconds, with a standard deviation of 0.087 seconds, so that we could expect 95 percent of the times to fall in the range 0.95 to 1.63, as indeed they comfortably did (1.04 to 1.47).

    Taking the local acceleration due to gravity to be 9.805 metres/s/s gives a height of 8.16, an error of nearly 30 percent. This would give a dip error of 0.8 arcmin.

    The error is in the right direction. If one assumes a timing error of 0.1 seconds (and you don't have to be old and decrepit to have such an error when operating a stop watch), we get a much closer 6.9 metres.

    The linked photograph shows the bridge of the Baradozic ;-)>

    Bill Morris
    Pukenui
    New Zealand
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