Associated Topics || Dr. Math Home || Search Dr. Math

### Defining a Sphere

```
Date: Thu, 01 Dec 1994 22:27:38 -0400 (EDT)
From: Kendall
Subject: Sphere

Dear Dr. Math,  My math teacher asked me to send you this math question.
There seems to be different information about spheres in our old math book
and our new one.

A sphere has Zero flat faces, Zero vertices, Zero straight edges,
Zero curved edges and ONE curved face.

Harcourt Brace Jovanovich _Mathematics Plus_ 1992 shows:
The same information EXCEPT it says ZERO curved faces.

Is one right and the other wrong or has someone made a change? My teacher
needs to know which way it should be taught.

- Kendall
```

```
Date: 7 Dec 1994 01:35:35 GMT
From: Dr. Math
Subject: Re: Sphere

Hello there Kendall!

Many mathematicians have intense debates over how to define objects like
this.  The problem is that nobody is right and nobody is wrong, since you
can define anything you want to define, and then you see what those
definitions give you.

I must admit, I tend to agree with the first definition of the sphere,
because when I look at a sphere, I see a curved face.  When I try to
picture the sphere they described with ZERO curved faces, I have a tough
time with it.  It doesn't make sense to me.

Of course, I have an entirely different definition of sphere that I like.
I define it as the set of points that are equidistant from a given point.
That point is the center of the sphere.

So it's kind of a matter of personal preference, since every good
definition of something is equivalent to every other good definition of it.

I hope this helps the debate.
```
Associated Topics:
Elementary Definitions
Elementary Geometry
Elementary Three-Dimensional Geometry

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search