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Topic: REPOST: New Sketchpad files available via FTP/Gopher
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Annie Fetter

Posts: 524
Registered: 12/3/04
REPOST: New Sketchpad files available via FTP/Gopher
Posted: Mar 2, 1994 4:07 PM
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[Originally posted Fri Feb 18 13:34:18 1994]

The following is the README file from a set of Sketchpad files now
available on the Forum ftp/gopher site (soon to be a Mosaic site, as

The sketches are currently in Mac form only, as a self-extracting, binhexed
archive, and can be found as


I hope to have a zipped PC version of the file available early next week.

If you have any problems with these files, or have any questions about how
to retrieve things via ftp or gopher, please let me know.



What follows are descriptions of sketches made by Bill Finzer, Rob Berkelman,
and Dan Bennett while employed at Key Curriculum Press in Berkeley. If you
would like more information about the sketches, feel free to contact me
(Rob) at or by calling Key Curriculum Press at
1-510-548-2304. We hope you enjoy the sketches as much as we enjoyed creating
them. We would love to see any work that you have done with these or
other ideas using Sketchpad.


Four ants located in the plane--each crawls continuously toward the next
ant. What paths do the ants describe? The sketches and scripts in this
folder show how to investigate this with Sketchpad. Try generalizing to
more ants, or (?) fewer ants.

Chase Four
This is a completed sketch. Move the starting places of the ants to
see the paths change.

Chase Four Starter
Use this sketch as a starting place from which to run the script.
This enables you to set your own number of steps that the ants take.

Chase Four.Script
Use this script in conjuntion with ``Chase Four Starter'' to move your
own ants.


These two sketches demonstrate useful Sketchpad animation techniques.
``Clock'' shows how to the hour and minute hands at different rates.
``Clock Switch'' shows how to turn analog motion into digital switches.

Derivative and Integral:

Sketchpad can nicely demonstrate elementary calculus concepts as
these two sketches show. In each sketch two graphs of curves
appear, approximated by a few data points. The bottom graph shows
the derivative of the top graph; i.e. the y-coordinate of each
point on the bottom represents the slope of the segment joining the
two points above it in the top graph.


You can move the points in the derivative graph and see the effect on
the graph at the top.


You can move the points in the top graph and see the effect on
the derivative.


Jean Marie Laborde (the creator of Cabri Geometri) has shown how
to model force fields. These two sketches demonstrate the techniques.


Here a capacitor is modeled with five positive charges on one side
and five negative ones on the other. You can ``see'' the nearly
uniform field between the two rows of charges.

Plus and Minus Charges

A test charge is moved around in the presence of fixed positive
and negative charges.

Exponential Sketch

This is a dynamic model of the exponential function where
the base of the exponential function is equal to the ratio
of length of two line segments. The equation is also
dynamically updated.

FPU Necessary:

Don't try these sketches on a slow machine. Too frustrating!

Compleat Sine Wave

You can use this sketch in demos in trig class to illustrate the
roles of amplitude, phase, and frequency in a sine curve.

Fourier Series

This geometric model of a Fourier series allows you go specify
the amplitude of components and shows you a neat way to visualize
how the wave is generated.


Here we have a sketches showing the platonic solids in true
perspective. You have control over the placement of the picture
plane, the station point, and the horizon. An animation button
rotates the figure for you. Some of the sketches show in 3D if
you have a pair of 3D glasses. (The colors may be a bit off on
your monitor.)

Linear Sketch

Here is a draggable line on an xy-coordinate system that
dynamically updates the equation of the line.


The midpoint quadrilateral, constructed by connecting the midpoints
of any quadrilateral, is always a parallelogram. Under what
conditions is it a rhombus? Use this sketch to investigate.

Navajo Rug

This is a sketch of a tessalation made in the pattern of a
Navajo rug.


This sketch was created recursively, replicating a segment
and an angle thus creating various polygons when the angle
is changed.

Parallelogram Area vs.Per

This is a figure which is minimally constrained to be a
parallelogram with constant area and perimeter.

Pendulum Experiment

Here is an animation of a pendulum. You can vary its length and
amplitude. Take some data. What is the dependence of the period
on these two parameters. Does it behave like a physical pendulum?


This is a dynamic perspective drawing of a road and
a railroad track receding into the distance.


This is a dynamic polygon generator created using the same
techniques as in N-gon but using two different angles and two
different lengths of segments, all of which are changing at
different rates.

Stochastic Geometry:

Here we have five scripts that demonstrate ways to use Sketchpad to
investigate random phenomena.

2D Fractal Mountain Script

Generate a random, fractal skyline.

3D Landscape Script

Generate a 3-D landscape using random fractals.

Random Walk.Script

Select a starting point and a segment that specifies how large the
steps are. The depth of recursion indicates how many steps will be
taken. Each step is in a random direction.


Select any two segments and run the script. You will get a
collection of random length toothpicks within the parallelogram
defined by the segments.

Thrown Ball

With a simple script, you can model the motion of a ball in a uniform
gravitational field. With a bit more work, you can find the focus and
directrix of the resulting parabola. Finally, you can animate a ball
along the path. This sketch could present some very good challenges for
advanced students!

Wittgenstein Thought:

These two sketches illustrate a problem posed by Wittgenstein.

A stick passes through a sleeve (in which it can smoothly slide).
The sleeve is nailed to the wall. As one endpoint of the stick
describes a circle, what does the other endpoint describe?

Be sure and look at Witt Engine before Witt Path.

Witt Engine

Here is a straightforward demonstration of the problem.

Witt Path

In this sketch the path is shown dynamically as you vary
the parameters.

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