Hi Friends. Thank you all. My main challenge is the "Hello World" , but in a scenario of a spring , one meter from the floor , with a mass on the top , as conected systems , and having a animation of the fall ... The equations will be another issue , once we will have this parameters on the real time during the lunar landing. ( http://www.googlelunarxprize.org/teams/spacemeta ). I m still thinking if Mathematica is a good tool for it , but it smell really good. Thanks ...

The first step of Sean's first step is to chose variables describing the system and then write down the equations of motion, using F = m a or Lagrange's equations, etc.