Metric System

Discussion in 'Woodturning Discussion Forum' started by Bob Chapman, Jul 14, 2014.

  1. hockenbery

    hockenbery AAW Advisor Staff Member

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    The original definition of the kilometer was that it would be 10,000 of them from the equator to the pole along a meridian. A very similar definition to the knot since that is also a 90 degree arc of latitude.

    This would make the Meter 1/10,000,000 of that distance. When French made the calculations they came up with a meter that was .02 mm short and that became the standard.
     
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  2. Bill Boehme

    Bill Boehme Administrator Staff Member

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    It ought to be noted that the SI system (what we refer to as metric) isn't purely decimal. There are still 24 hours per day and 360 degrees in a circle. Nautical miles and knots make a lot of sense for navigation and are used for both ship and aircraft navigation. The grad unit for angle measurement never caught on ... 100 grads vs. 90 degrees in a quarter circle .... Why would 400 grads be any better than 360 degrees in a full circle. At one time the speed of light was defined as three hundred million meters per second ... then it was discovered that this isn't exactly correct so something had to give. The speed of light is a constant so the meter was defined as the distance light travels in 1/299792458 of a second. Imagine if that had been the original proposed definition of the meter ... It surely would have been DOA.
     
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  3. Pete Copeland

    Pete Copeland

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    Bill,

    Mostly good stuff there but you are wrong to suggest that the length of a day has any bearing on the characterization of the System International de Unité. If you insist on using the SI system, then the time it takes for the Earth to make one rotation is 86.4 kiloseconds. It's more convenient for folks who otherwise use SI units to use days or years as units of time (or if you a geologist like me, millions of years) than using the official SI unit, the second. Days are not SI, hours are not SI. Nothing but seconds is SI. That doesn't mean using days or years is a bad idea, but once you do, you are using a hybrid (or at the very least, derived) system. So, SI is 100% decimal. When important things we need to measure don't come out as even powers of ten, it is the fault of the things, not the measuring system.
     
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  4. Gerald Lawrence

    Gerald Lawrence

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    Just wondering what the length of a day or distance to the pole from the equator has to do with turning?
     
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    The metric system isn't any better nor worse than the
    How many days would it take to turn a pole that long? Woodturners usually don't measure things except using the thumb and eyeball system.
     
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  6. Mike Johnson

    Mike Johnson

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    Measuring the depth of a bowl is now pretty easy if you just hold a flash light across the rim
    of the bowl and turn the light on while counting how long it takes before the light illuminates
    the bottom of the bowl. :)
     
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