Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Cable around the Equator
Replies: 10   Last Post: Jun 17, 2012 2:29 PM

 Messages: [ Previous | Next ]
 Pat Ballew Posts: 356 Registered: 12/3/04
Re: Cable around the Equator
Posted: Nov 6, 1996 2:42 AM

Sane or not, it is correct, but more surprising perhaps, would be
that if Ma Bell did the same thing to the circumference of every
planet in the solar system (add 50 ft to the circumferenc) the height
of every one of the cables thus hung would be exactly the same height
from the surface of the planet.
Insane... yes, Insanely beautiful that reality defies our
perceptions, but not our mathematical logic.

Pat Ballew
MIsawa, Japan

Subject: Re: simple geometry puzzle -- SPOILER
Date: 11/5/96 4:43 PM

How can adding 50' of slack to the cable spread evenly around the equator
pass the sanity check! This is why we must not blindly accept mathematical
results. That is the lesson to be learned from this geometry problem.

lipp@educ.umass.edu wrote in article
<Pine.PMDF.3.91.961104130200.557939369A-100000@oitvms.oit.umass.edu>...
>
>
> On Mon, 4 Nov 1996, mfr1 wrote:
>

> > Ma Bell wants to place a telephone cable around the equator. She adds
50
> > feet to the length of the cable beyond what is required. This slack in
the
> > cable allows the cable to be strung up above the ground. How high up
from
> > the surface of the earth will the cable stand? You can assume that the
> > earth is a perfect sphere.
> >
> > In your mind, run a sanity check on your answer to see if it makes

sense.
> >
> Surprisingly, you will be able to walk under the cble easilty. Since the

> circumference of a circle is C = 2piR, each increase in R obf 1 foot
> increases the circumference by 2pi feet. since the cable has been
> increased by 50 feet the radius of the cable-circle will be increased by
> 50/2pi or about 8 feet!
>
> Alan Lipp
>

Date Subject Author