Re: A Question of Physics 101
- From: "efgh" <efgh@xxxxxxxxxxxxx>
- Date: Sat, 21 Apr 2007 15:06:38 GMT
"Roy Smith" <roy@xxxxxxxxx> wrote in message
In article <ncpWh.23932$PL.22433@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Glen <gNOSPAM@xxxxxxxxxxxxxxxxxxxx> wrote:
"GROVER" <joseph.golaine@xxxxxxxxx> wrote in messageI was in HS when they built the Verrazano Bridge in NY. I remember one
Since I've been enjoying the topics and discussions of this news
group, and I see that there are many posters who are quite bright, I
decided to pose a question concerning the laws of physics to
stimulate the group's curiosity.
The question is: If you hang two plumb bobs, say 50 feet apart are the
I would say they are as close to parallel as one would care for them to
If you want to get technical, they are not exactly parallel due to the
curvature of the earth. One would assume that the bottom of the plumb
is pointing at the exact centre of the earth due to gravity and since
on a ball, they wouldn't be exactly parallel. At 50 feet apart, the
difference wouldn't be enough to care about.
of my teachers explaining that the uprights had to be 6" out of parallel
due to the curvature of the earth. I don't know if the number is
accurate, but that is what I recall (after forty years or so).
Let's do some quick math.
The towers are about 700 feet tall, and the Earth's radius is about 4000
miles. 700 feet / 4000 miles is about 1 part in 30,000.
Since arc length is proportional to radius, the tops of the towers are 1
part in 30,000 further apart from each other than their bases. The towers
are about a mile (call it 5000 feet) apart, so the tops are about 5000 /
30,000, or 1/6 of a foot further apart than the tops. Call it two inches.
Now, let's got to the video tape. Wikipedia says:
Due to the height of the towers (690') and their distance apart (4260'),
curvature of the earth's surface had to be taken into account when
the bridge -- the towers are 1-5/8 inches farther apart at their tops
Not bad for back of the envelope, huh?
You're a star. :)
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