Thanks for these modifications.
It seems to be a problem while if r > 0.6, g don't change anymore.
As the gravitation field is concerned, would it be possible to have it as an option because I work with 15 years old students and it will be difficult for them to understand the meaning of such a field ?
Can we have instead a cursor where m of the object can be changed and the value of force would appears in the simulation ?
thanks in advance,