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CD School House 9.0 - Wayzata Technology (1994).iso
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gravity.doc
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1989-01-14
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GRAVITY v1.0 - (C)opyright Steve Safarik, Chico CA. Jan 08 1989
This program was inspired by the Macintosh program "Gravitation" which
can be obtained from Jeff Rommereide at PO Box 600, Sicklerville NJ,
08081.
Registration of this version is as follows: Regular users - $10.00;
Government, Corporate, and Educational users - $20.00. Only one regis-
tration per address is necessary. Please send payment to Steve Safarik,
1076 Tracy Ln, Chico CA 95926. Support the Shareware concept!
This program was designed to let a person experiment with
the orbits of planets as they may occur in the universe.
The motions of planets can be very interesting to watch as
each planet affects other planets via its gravitational force.
First time users:
Use the arrow keys and ENTER to make a selection from
the menu bar. The first thing to do is to select an
example from the Samples menu. Watch it run, then
experiment by changing the values of various planets
with the Editor. Values which can be changed are: Mass,
X position, Y position, X velocity, Y velocity, Trace
Enable, and Stationary Enable. The center of the screen
is X=0, Y=0, with increasing X values to the right, and
Y values increasing upwards.
Advanced users:
Under the File menu, you can save and restore setups
entered via the editor which are pleasing to you.
Under the Misc menu, you can toggle several items: Tracers
on all planets allowed or disallowed; Drawing of the grid
points on/off; and finally, write to the screen directly to
memory for close IBM compatibles, or through the BIOS for
less compatible machines that print garbage on the screen
instead of the correct picture.
Under the Utility menu, you can adjust several constants
which affect the way planet positions are calculated. The
Gravitational Constant is a measure of the strength of the
gravitational field; and the Time Factor determines the
length of time a force acts on a planet. The Time Factor
relates to the accuracy of the positions of the planets,
smaller values being more accurate. Larger values will
speed up the motions of the planets.
Also under the Utility menu, you can change the type of
display hardware to be used in case yours is incorrectly
detected. The display to use can also be specified on the
command line. Start program with GRAVITY /? for a list of
available switches.
Speed notes: I've tried to make this program as fast as
possible, but there are a few trade-offs I had to make. For
one, accuracy must be sacrificed to gain speed. You can
twiddle with the Time Factor yourself to see this. If you
want to speed up the action, you can do three things:
1) Increase the Time Factor and live with slightly less
accurate orbits, 2) Change the display mode to a lower
resolution, such as CGA, or 3) Buy an 8087 math coprocessor.