How to use the Planetary Motion program.

The planetary motion simulation displays what the orbits of Venus, Earth, and Mars would be, given different masses. The graviational law of physics states that the larger a mass of an object is, the more gravitational attraction it has with other objects. This can be displayed with this program. When the user makes the mass of a planet very large, the other planets are "drawn" towards the massive planet, and are eventually flung from the solar system.

Planets.tcl is an interface for a planetary motion program, written by Paul Woodward and modified by Rich Solstad. When the interface is run, the user is presented with three planets, and is asked to increase the mass of each of the planets by a certain factor. An option is also given to let the user decide if planetary trails will be shown or not. If they are not, then the planets will simply be three large circles orbiting the sun; if they are displayed, then the planets are shown as lines, and the paths they have taken are displayed. The user also has the option of clicking on any of the three planets to view information on that planet. One, two, or all three planets can be displayed at once, and the user can compare and contrast statistics about each of the planets this way. Once everything has been entered, the user clicks the "Start" button, and watches what the resulting orbits of the planets would be, given the changed masses. A control bar is presented in the upper-left hand corner of the screen, allowing the user to "stop" the simulation, or to "pause" it. If the user pauses the simulation, it will resume only when the "resume" button is pressed.


1) Pressing the "pause" button during a simulation sends a signal to the underlying planets program, telling it to temporarily stop. This sometimes isn't done instantaniously, so the program doesn't always stop exactly where you wanted it to.

2) The program has limited functionality at this point. In a newer version, the user may be allowed to do things like change the number of planets in the system, change their starting locations, etc. Currently, only mass can be changed.


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