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

 Search Thread: Advanced Search

 Messages: [ Previous | Next ]
 Art Mabbott Posts: 142 Registered: 12/3/04
Re: Cable around the Equator
Posted: Nov 5, 1996 7:23 AM
 Plain Text Reply

What also challenges your sanity is that it matters not the size of the
original sphere....it could be the size of the earth as in the original,
or the moon, or a beach ball or even the size of a golf ball. My kids
have a tough time accepting the "real mathematics" as the correct (sane)
answer. They initially don't believe their numbers. But we work at it.

Art Mabbott
******************************************************************************
From the Net: mabbotta@belnet.bellevue.k12.wa.us
From the Web: http://belnet.bellevue.k12.wa.us/~mabbotta
__ _______
| | / | Newport High School
| `-'* | 4333 128th Ave. S.E.
| | Bellevue, WA 98006
|_ | (206) 455-6136 (Work)
\__________| (206) 746-5449 (FAX)
(206) 883-6087 (Home)

On Tue, 5 Nov 1996, Juan Miguel Vilar wrote:

> Not only was his math impeccable, it was also correct! I think that
> it passes correctly the sanity check, where is the problem?
>
> Juan Miguel Vilar
>
>
> On 5 Nov 1996, mfr1 wrote:
>

> > How can adding 50' of slack to the cable spread evenly around the equator
> > add 8' at each point? Your math was impeccable but your answer does not
> > 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
11/4/96 mfried1@earthlink.net
11/4/96 Alan Lipp
11/5/96 Pat Ballew
11/5/96 Art Mabbott
11/5/96 mfried1@earthlink.net
6/17/12 Taylor
11/5/96 Bernard Domroy
11/5/96 Juan Miguel Vilar
11/6/96 Charles Biehl
11/6/96 Pat Ballew
11/6/96 DougKuhlmann-PhillipsAcademy-Math

© The Math Forum at NCTM 1994-2018. All Rights Reserved.