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GRAVITY
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Nick Hutton takes a walk around the galaxy with some learned friends.

A few weeks ago, when we were still enjoying a good summer, I was sitting in my garden. As I leafed through last months esteemed organ (that's ACU folks), a large pome-granite fell from the tree I was sitting under and struck me on the head. "Eureka!" said I, as the product of all those dim and distant A Level Physics lessons came flooding back to me. Simultaneously I had the inspiration for this months listing.

The following program will allow you to analyse the behaviour of celestial bodies and the interaction thereof. It uses Newton's laws of force and motion to simulate a theoretical corner of the universe. For a full and complete breakdown of all its features I'll hand over to my learned friend Sir Isaac Newton (who usually plays only shoot-em-ups on his CPC). Take it away Isaac.

I.M. Thanks Nick.

Well as Nick said, with this listing you can sit back and watch as my laws of force and motion are put into practice. To get started then select option 1. The built in example, this illustrates the Earth Moon orbit. Or press 2. if you want to input your own data from one of the tables or just make some up. If you wish to draw a graph of the paths which will be plotted to screen then select option 3. The simulation will run but instead of the initial data being at the top of the screen, you will see a list of co-ordinates to plot. These co-ordinates are colour coded to correspond with the celestial bodies on the screen. It is then a simple matter to draw up a sensible scale on graph paper and then plot every ten or perhaps twenty values.

If you have an Epson compatible screen dump somewhere amongst your disk collection then press CTRL to get a seventeen K screen file onto disc, sorry not tape. It is then up to you to obtain your hard copy from the aforementioned screen file.

Newtonian Physics does take a few minutes to sink in so why not enter one of the printed examples elsewhere on this page. This should give you an idea of what sort of data is required. For a complete explanation of these examples 111 let my colleague Mr Johannes Kepler take the floor. (He was given his CPC6128 last year for his 419th birthday).

J.K. All Hellow readers, and thank you Isaac. I'd like to get back to my 6128 so I'll be as brief as possible. Now onto the examples:

1. Earth Moon Orbit
After entering the data you will be able to see the Moon travelling alongside the Earth. The Moon has the required mass and velocity to orbit without being pulled into the Earth, but is is not massive enough or fast enough to escape the Earth's gravitational field.

2. Binary Star system

This example will simulate the interaction of two binary stars like Delta librae in the constellation of Libra. The stars have the required mass, velocity and gravity to orbit around a common centre of gravity.

3. Slingshot satellite manoevre

When we wish to observe a distant planet in detail we must use an exploration satellite. Voyager II was launched to observe many such planets, but to travel directly to each planet it would have needed a vast amount of fuel. To reach distant planets, scientists had to develop another method of propulsion.

So the slingshot manoeuvre came into being. A satellite uses the gravitational field of a more massive planet to fling it off at great speed onto the next object which is to be studied. The data provided will give a reasonable simulation of this carefully calculated operation.

By the way this method of travel will be used by the Magellen solar probe, when it slingshots around Jupiter on it's way to the Sun.

4. Anti Gravity

What would happen when one planet drifted towards another planet and the force of gravity were reversed? Well, now you can find out Observe as both celestial bodies drift towards one another, and then as the force of anti-gravity takes effect and they slowly glide apart.

That's about it example wise, so it's back to Nick for a little more about the programs functions.

NH

Just type in listing one, as it appears and run it. Ifyou want to enter your own data or input one of the examples then select option 2. If you wish to use the built in example choose option 1.

By the way the machine code interrupt driven screen saver is printed separately as well as in listing 1. I'm sure many of you will find it useful as a stand alone piece in code. It lives fairly high up in memory but this positioning can be easily altered to suit your own needs. Perhaps you could relocate it in the non-volatile area of RAM around &AF00. You can select option 4 to quite the simulation and resent your machine.

Ifyou discover some really interesting astronomical manoeuvre then why riot send in the data. Great fun can be had crashing Halleys comet into the Earth, so why not have a go at plying God with the universe. So until next time its goodbye from Nick, Esaac and Johannes.

ACU #9101

GRAVITY (AMSTRAD COMPUTER USER)
(c) AMSTRAD COMPUTER USER

AUTHORS: Nick Hutton and Isaac Newton

★ YEAR: 1990
★ LANGUAGE:
★ GENRE: ARCADE

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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.