We saw that when the scene is animated, the particle doesn't move, just like the first scene in this tutorial. However, contrary to the first scene, our scene now results in a simulation being launched, forces accumulated, and an ODE computes the new positions and velocities! To be sure of that, we will add one particle to the MechanicalObject. The particle of index "0" will still be constrained to its original position.
We have resized the MechanicalObject, and added another particle at the position (1, 0, 0).
The particle marked by a pink square is still fixed, while the other falls due to gravity.