Universal Gravitation Model 
To build this model, students start with the ActionReaction 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. 

Vensim Version

STELLA Version

NetLogo Version

