Universal Gravitation Model

 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 GravitationVensim STELLA Version isee Player Software Right-click to download the model 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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