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Chapter 2 The Model
I used to love mathematics
for its own sake, and I still do, because it allows for no
hypocrisy and no vagueness....
~Stendhal (Henri Beyle), The
Life of Henri Brulard
The model I’m going to describe is based on
one simple formula: y = a^3/ (a^2 + x^2). This formula has
been around since the early 1600’s and has an interesting
history of three prominent mathematicians of the 1600’s and
1700’s that studied it. Chapter 13 is devoted to just the
history of the formula, and while the history is fascinating it
adds no value to the model.
The name of the curve that the formula
develops is called “The Witch of Agnesi”. In the research I’ve
done I have found nine or ten different versions of formulas
called The Witch, and
while they all produce a similar curve, I am only using the one
stated above. This version of the formula was created by Maria Agnesi and has a drawing that shows her thought process. This
drawing begins the framework for the model.


Figure 2-1
I am going to start with her drawing and
explain some of the basics. I will then begin to convert her
drawing to a three dimensional model, step by step.
The math required is 7th or 8th
grade with a small amount of trig thrown in. I am including
many drawings that I think will help in the visualization of
what is happening. Each drawing is a step towards understanding
what is happening.
If you are familiar with statistics you are
probably thinking this curve looks like a “Normal” or “Gaussian”
Curve”. It was this shape that drew me to it, and while it
looks like a Gaussian Curve it has its differences. See chapter
12 for the differences.
This is a mechanism that would produce the
original curve.

Figure
2-2
(C) is confined to move around the
circumference of diameter a.
With this model I have three ways to draw
the curve.
1.
At the top I can move [X] left (-) or right (+)
This changes
angle (c) which in turn moves [Y] up or down.
This just like
the formula states
2.
On the Left side I can move [Y] up and down
This also
changes angle (c) and causes [X] to move left or right
3.
Turning the Knob changes angle (c) which causes [Y] and
[X] to change.
A marking pen is attached to where
point [X] and [Y] cross and will draw the curve
on any movement
of [X], [Y] or (c).

Figure 2-3 Click on Figure to see animation.
This
shows the model with the curve drawn.
While I have not built this device I am
certain it would not be hard to make and it would be capable of
drawing the curve as shown. Building the model would pose one
problem that you may have already picked up on. The horizontal
lines (or bars in the model) and the line of bar for (c) would
need to be very long just to produce the curve above. To build
it correctly would require lines or bars of infinite length.
The fascinating thing about this model is
if you could build it (with the infinite lengths) just turning
the knob would give you a show beyond your wildest imagination.
If you were to start with the knob at the zero position (with (
c ) at the top) and start turning the knob slowly clockwise [X]
will begin to move. As it draws the curve you will notice that
[X] starts moving faster to the right with each degree. As you
approach the 90 degree mark [X] would be miles away, millions of
miles then billions of miles moving father and faster with each
slight turn of the knob. You are now at 89.999999999999999999
degrees moving faster and farther. Then at 90 degrees you have
finally reached infinity (whatever that is). Amazing! But
what happens if I turn the knob .00000000000000000000001 degree
further? When you just begin to turn the knob past 90 degrees
[X] instantly goes from plus infinity to minus infinity.
Making the Model Circular
The model we are going to build attempts to
get around the infinity problem by making the model circular.
You might be thinking that this will really complicate the model
and we will get bogged down in doing a lot of trigonometry, but
actually the math is no more difficult than the original model.
The key to this is to work in radians instead of angles.
Some of the people that have seen this
model struggle when dealing with radians.
If you are not familiar with radians or it
has been a long time since you have used them, here is a quick
refresher on them. Note: “r” is the radius of the circle.

Figure
2-4
Working in radians allows me to talk in
units of length that simply wrap around the model without
working with angles and the trigonometry associated with them.
The use of radians becomes important
in the
next step of the model HUH 2; it is circular, not flat like HUH
1.

Figure
2-5
In the 2nd step model, HUH 2, we
take the flat [X] plane that forces us to deal with infinity,
into a circular world that hopefully will confine infinity but
still retain infinity’s most important property of “length
unknown and unknowable”. HUH 2 takes a somewhat more rational
approach, using “distance unknown and unknowable”. We
currently view space and infinity as pretty much the same
thing. When we reach the end of space we are at infinity. If
space were circular when we get to the end we simply start over
with the distance traveled continuing to increase. Fig. 2-5
shows what would happen if I turned the knob 90 degrees
clockwise. On the larger circle I would have made it ¼ the way
around while on the small circle I would have made it ½ way
around.

Figure
2-6
Fig. 2-6 shows what a mechanical version
might look like.
The circular form of the model does not
draw the nice looking bell curve like the linear model does.
Actually the curve that gets drawn looks kind of ugly as shown
in Figure 2-7.

Figure
2-7
The shape is developed from “Z” that is an offset amount
from the base [X] and is trying to form the bell curve inside the starting
diameter.
Figure 2-8 shows what the mechanical device would
draw:

Figure
2-8
If you look at Fig. 2-6 and think
about turning the knob, when you get close to the 90 degree
point the model will begin to bind up.

Figure 2-9
Fig. 2-9 shows the beginning of the
problem, as the knob turns from the center of the large circle
from 0 to 90 degrees, pi/2 radians are needed. But on the
smaller circle pi/2 radians is 180 degrees. When we turn the
knob 90 degrees we get what is shown in Fig. 2-10

Figure
2-10
I am going to have pi/2 too many radians
and no place to put them when I turn the knob another 90
degrees.
We now have the core of our model. This is
a very simple visual model with the only problem being that it
won’t work.
Summary:
-
Think in Radians. If you don't
understand them take the time now before continuing.
-
Think about how to deal with the
excess radians (the next chapter has suggestions)
Chapter 3 will show what is needed to make
it work. |