"Gravity"
By Fred Rodney
1984
ARCADIAN 6, no. 5 (Mar. 30, 1984): 41, 42
AstroBASIC


This Arcadian program was found in the Bob Fabris Collection; it includes a 
text title screen.


From the submission letter to Bob Fabris:


Dear Robert Fabris,

"The enclosed tape, inspired by the Commodore 64's "Visible Solar System," is 
an AstroBASIC program that you may wish to publish in the 'Arcadian.'"

I hope that it can supply future programs that will deal with other aspects of 
space and physical laws.  I hope others will submit programs too, to make a 
kind of "Arcadian" series of educational programs.

Fred Rodney

P.S.  The "Gravity" program enclosed was written by me and is, to the best of 
my recollection, an original program that does not intentionally use 
unauthorized material from other sources.  The program is for the enjoyment and 
use of "Arcadian" readers.


Fred also included extensive instructions in his original BASIC LISTing.  They 
are much more elaborate and detailed than the insturctions originally included 
with the "Arcadian."  Here are Fred's original instructions:


*Gravity* by Fred Rodney

You command the first fleet of interplanetary space probes.  You launch them 
from aboard your command post on the space shuttle Enterprise.  All probes are 
capable of hovering over any planet at 2000 feet (except Pluto) and each can 
escape back into space to perform gravitational tests elsewhere.  The probes, 
however, cannot escape from the gravity and heat of the sun.  All probes that 
enter the solar atmosphere for tests will disintegrate, but not before sending 
you the data you seek.  You are left, upon disintegration, with a scene of the 
night sky from a telescope on your space shuttle.  Since you have an unlimited 
supply of space probes, the disintegration of a few should not concern you.  
Begin with a probe on Earth, for reference.

INSTRUCTIONS: Load the program and the *() array. There is one byte of RAM left 
on both sides of the array (buffer) so be careful. Run the program. First, you 
should see the night sky followed by the program title, a little music, and the 
exhaust from the launch of your shuttle craft. Then a map of the solar system 
will appear as a reference, with the massive sun on your left. Finally, a menu 
will appear. Choose a planet to probe from this list by entering the proper 
number on your keypad (Pluto is not listed because its gravity is not known). 
After you enter your choice, the map will reappear, highlighting your choice 
(showing its relative position in the solar system). The screen will then shift 
to a scene of the planet's surface, with your probe positioned at 2000 feet 
above the surface. The name of the planet will be on top with its relative 
gravitational constant (Earth=1) and a seconds clock on the left. After 
signaling, the probe will release a weight and the clock will time the weight's 
moment of impact based on the formula: H=1/2gt^2 or t=sqrt(H+1/2g). The menu 
will reappear and further tests on other planets may be made.

Because of the Astrocade's limited memory, you can only test for gravity with 
this program. Therefore, this program is called a chapter in a proposed series 
of educational programs that were inspired by the Commodore 64's "Visible Solar 
System" cartridge. Future programs will visually compare other features of the 
solar system and perhaps a venture to another star. Arcadian readers are 
encouraged to submit "chapters" to this Astrocade Educational "Library." All 
programs should be factual and fun, and in this context, this program includes 
a few graphic surprises, using nothing more complicated than an &(9) port 
setting.

---------

One final note: Don't attempt to set your watch by this program's clock. The 
final time readings are correct and can easily be checked with a calculator. 
And this is what really matters. Limited memory precludes the use of the 
Astrocade's RM variable, I simply felt that the added "frills" were more 
important because an educational program must be interesting to be used, 
especially by children. Leave exact seconds (rate of seconds to be precise) to 
the Analog Clock by George Moses. In addition to the above, the relative 
gravity constants have a range of 175 with the sun included, but is only *17 
without the sun. Most of the activity takes place within this small range, but 
with the sun included, a difference must be demonstrated within the range of 
*17 without having to go overboard to demonstrate the tremendous gravity of the 
sun,

*The column of pixels in the center of the map represents the asteroid belt.

