To build this model, students start with the Action-Reaction model and make modifications to it. They are told that a future model (Coulomb's law) will require them to reference this model. It is hoped that a comparison of the models will help them internalize the similarities and differences in the two mathematical relationships. Samples of modifications to this basic model may be found at Universal Gravitation Model Extensions.

THE MODELS

Vensim Version Vensim PLE Software Right-click to download the model Universal Gravitation Vensim

STELLA Version isee Player Software Right-click to download the model Universal Gravitation STELLA PC Universal Gravitation STELLA Mac

NetLogo Version NetLogo Software Right-click to download the model Universal Gravitation NetLogo

NETLOGO MODEL STELLA MODEL [Diagram Level | Equations Level | Graphs ] position_1(t) = position_1(t - dt) + (rate_of_change_of_pos_1) * dt INIT position_1 = Initial_Position_1 rate_of_change_of_pos_1 = velocity_1 position_2(t) = position_2(t - dt) + (rate_of_change_of_pos_2) * dt INIT position_2 = Initial_Position_2 rate_of_change_of_pos_2 = velocity_2 velocity_1(t) = velocity_1(t - dt) + (rate_of_change_of_vel_1) * dt INIT velocity_1 = 0 rate_of_change_of_vel_1 = accel_1 velocity_2(t) = velocity_2(t - dt) + (rate_of_change_of_vel_2) * dt INIT velocity_2 = 0 rate_of_change_of_vel_2 = accel_2 accel_1 = net_force/mass_1 accel_2 = -net_force/mass_2 Distance_between = position_2-position_1 Initial_Position_1 = 0 Initial_Position_2 = .2 mass_1 = 6E6 mass_2 = 6E6 net_force = 6.67E-11*(mass_1*mass_2)/(Distance_between)^2 Time Specs Settings Range: 0-2; dt = 0.05; Integration Method = Runge-Kutta 4

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