Date: Sat, 30 Jun 2012 06:32:28 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: EPA and Vanagon Emissions
In-Reply-To: <4FEEA6AE.5060704@turbovans.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Hi Scott - gerry is down, by the way, along with three million other
power customers between IL and VA.
At 03:11 AM 6/30/2012, Scott Daniel - Turbovans wrote:
>how come there is only one time system around the world ? Why is it
>all seconds, minutes, and hours everywhere..
Convenience, I should think, especially of navigation and
commerce. It's tied in with angular measure, since an hour is
fifteen degrees, and a minute of latitude is very close to one
nautical mile (and a nautical mile is one minute of longitude at the
equator). Once you've decided on 24 equal-length hours and 360
degrees the minutes flow from geography and seconds from minutes.
Cultures start caring about precise time measurement about the same
time as they take up astronomy, I suspect. Navigators start caring
strongly about a definite correspondence between linear, angular, and
time measure as soon as they start trying to navigate by
astronomy. Once they're able to carry an independent time measuring
device with them (a chronometer, that is) they also need a prime
meridian to make reference to in calculations of longitude.
>and doesn't some culture somewhere have another system for units of time ??
Well, there's Swatch Internet time, and some of a geekish cultural
persuasion use it. I believe some Chinese ancient society used a
hexadecimal measurement of the day. Right after the French
Revolution France was using a decimal time system, but it didn't last
long. I believe they were also pushing for 400 degrees in a circle
at one point, not sure. Surveyers use that, they call them grads
instead of degrees. And various military outfits use mils
(milliradians) for specific purposes, because for small angles each
mil gives you one meter (or whatever unit) height per thousand distance.
But I'm not aware of any culture engaged in world communications or
commerce that hasn't adopted the HMS system.
>When was the concept of hours and minutes invented, and by whom ?
Romans had a twenty four hour day, divided into twelve day and twelve
night hours, the hours being of varying length by season. About as
handy to calculate with as their forgetting to invent the zero and
cyclic numerals. Constant-length hours and minutes I couldn't
say. If I had to make a wild guess, it would be some combination of
Greeks and seamen, since Greeks had quite an interest in astronomy
and seamen in navigation which is bound up with same.
>Wait until I say why things fall over . Or what feature makes
>something tippy and something else stable .
>That's too easy. People should be able to say what makes something
>tippy or not, if they think about it.
Huh? They fall over because their center of gravity is outside their
base of support. High-aspect-ratio objects (of uniform density) are
tippy because it's easy to achieve that with a small
push. Low-aspect-ratio objects with low centers of gravity are
difficult to tip.
>And when you see that, you will realize that a wheel is actually
>composed of a a point that is continuously falling .
Have to disagree there. Something in orbit around a planet or some
other mass is a point that's continuously falling (accelerating
toward the planet), but its horizontal vector is sufficient that the
arc of its fall never reaches the planet. But this depends on a
balance of inward acceleration and horizontal vector such that the
point neither escapes nor plunges to the surface.
A wheel on the other hand is a static object composed of an infinite
number of points all of which would like to be falling but none of
which are, because they're constrained by the structure of the
wheel. Even when the wheel is rotating (assuming it's balanced) each
infinitesimal point is precisely balanced by another 180 degrees
opposite which is being lifted, so the two cancel each other out. If
the wheel is unbalanced and allowed to rotate freely, yes; it will
oscillate with the heavy side alternately falling and rising until it
comes to rest with the heavy side down.
Yours,
David
