Cribbed from Wilkopedia's section on the Citibank tower in New York,
built in 1977:
To help stabilize the building, a tuned mass damper was placed in the
mechanical space at its top. This substantial piece of stabilizing
equipment weighs 400 tons and has a volume of 255 cubic feet (7 m³).
Designed to counterbalance the effects of wind by making the building
sway, it is a concrete block that slides on a thick layer of oil and
converts the kinetic energy of the building into friction. This mass
reduces the building's movement from wind deflection by 50%. Citigroup
Center was the first skyscraper in the United States to feature a tuned
Full article on the building here:
Yes, pretty wide. The widest I can think of is the reflecting pool at
the Christian Science Center in Boston, which is 686 feet long. The
water spills over a granite curb that surrounds the entire pool. The
earth's curvature over 686 feet is only 1/32". Walking through the plaza
on a windy day it's obvious that on this scale the wind is a much
greater influence than the earth's curvature.
The only time I ever got involved in compensating for such an rch in
something I was building was about a dozen years ago when I was making,
testing and calibrating some of cesium atomic clock controlled
oscillators which provide autonomous timing signals onboard each of the
We had to adjust the frequency of those units in the lab "off" by a
little less than one part in ten to the eleventh (IIRC) to account for
the relativistic and gravitational time shifts which occur when they
were whizzing around at orbital speeds and altitudes.
Further corrections are provide elsewhere in the GPS sytem to accomodate
for the satellites's orbits being a bit elliptical, so the velocities
aren't constant throughout each spacecraft's orbit.
AFAIK thats the only example of a consumer product, the GPS navigation
systems in common use today, which relies on stuff having to be built
and adjusted to those levels of accuracy.
Clearly, you don't get it.
But, sadly, I made another mistake.
It's far from 1/2", as pointed out by an amc'er. It's proly .05, just based
on ratios. <sigh>
But still, whenever I see a really tall skinny building now, I think of a
long truncated upside-down pyramid.
So g-d Elson AIN'T right!! :)
Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
Well, see this page for backup on my calculations :
Now, using their same equation ...
Ahh, this is too hysterical to do in miles, so I converted everything to
So, A^2 = (3963 * 5280) ^2 + 100 ^2 (for a 100 foot length)
Then, you have to subtract the radius of the earth, in feet (3963 *
convert feet to inches ...
I get .0029" of curvature over 100 feet. If I haven't made a mistake
here, then it does
come up smaller than what I was computing before. This isn't the only
compute this, and takes a couple of shortcuts.
Running the same computation for 1000' gives .287"
1500' gives .645"
Even at these incredibly small angles, the non-linearity of the function
clearly in the last 2 numbers.
The Earth's curvature is 8' per mile from what I remember... But taking the
diameter of the planet and using a CAD program, you could figure out the
difference based on height I suppose...
I always argue with a friend of mine that a 1 mile long "flat" runway would
actually rise well above ground level (4' on each end) unless it wasn't
truly flat - If it was built to the Earth's curve, it would actually be flat
to a level (which works on gravity) but not flat to a perfectionists rules.
...What's the point of this thread again? <G>
Joe Agro, Jr.
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