Universal Gravitation Extensions 
Since the first Universal Gravitation model was created, there have been several variations created.
This page provides links to pages which show the model and its graphs, a quick description of why the
model was created and the model's faults, and the models themselves. 
Name  Description  Rightclick to Download Models 
Basic Model  In the Basic Model, objects start at 0 and +0.2. Forces are "hardwired" for one direction. These objects pass by each other and accelerate rapidly away.  STELLA PC STELLA MAC Vensim 
Model with Stop  The Basic Model is modified so that the objects stop when they are within a certain radius. We still see a massive acceleration as they meet.  STELLA PC STELLA MAC 
Gravity on Earth  The Basic Model is modified to show an object falling to Earth. Students verify 9.8 m/s^{2} as Earth's gravitational acceleration on an object.  STELLA PC STELLA MAC Vensim 
Gravity inside Earth  This model answers the classic problem about an object passing through Earth. Note that Earth is treated as stationary. How could the original model be modified so that we could see the motion of the object and Earth's movement (if any)?  STELLA PC STELLA MAC Vensim 
Objects Recoil  Now the objects recoil when they contact, then return. Note that the "hardwiring" for direction has been fixed.  STELLA PC STELLA MAC Vensim 
Ball and Ring  What if a ball and ring are suspended near each other in deep space, far from any other gravitational influences? What behavior would we observe?  STELLA PC STELLA MAC Vensim 
