NetLogo User Community Models
by Ed Hazzard (Submitted: 08/30/2007)
This model is a modification of "Solar System" by Jerry James (2/13/03). It allows one to compare the orbiting times of the six historical planets. The original model focuses on the effect of a comet. This version focuses on the relative orbit times of the planets.
This model mimics the solar system. Setup creates the sun and five planets. Unlike in the real solar system, these orbiting bodies are in the same plane, and setup distributes the planets randomly. However, the planets are at the
To Run the Model
Just press Setup. Setup resets Zoom to 15, which shows all six planets. To view the motions of the inner planets, increase Zoom. The initial angle of each planet is preserved with a radial line.
Press Go. It may be useful to slow down the model using the speed slider above the graphic window. Or to search for a specific value, use the "go once" button.
If you want to confirm Kepler's Law that relates the radius of the orbit to the period, compare each planet to the earth. The Procedures show the radius of each planet's orbit, and the year monitors show the number of orbits (years) compared to the earth years.
The speed adjustment actually changes the size of time intervals at which the new planet positions are updated. This affects the accuracy of the orbits. At a speed setting of 10 there are about 1000 updates of the position of the earth per
While the Model is Running
To increase the speed of execution without affecting computation accuracy, turn the display off by pressing Display On/Off.
Computing the acceleration of object #1 towards object #2 due to gravity:
From F = ma = -GMm/r^2 and solving for the x and y components of acceleration a we get accx = -GMx/r^3 and accy = -GMy/r^3
Computing the inital conditions
After the planets are randomly placed at their proper orbiting distances from the sun, the initial velocities are computed
The initial accelerations are computed as described above, with each planet having the effects of the sun's and all the other
At each time interval a new x and y position for each planet and the comet is computed based on the x and y velocities for
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