Using Ogre or Irrlicht is like trying to get back at your neighbor by Bombing his house from space. Its overkill for small tasks. However, they are both frameworks that easily wrap up the API so its easy to use.

Quote:What would be the FREE game engine or combination of 3d and physics engine to achieve that goal very easy and fast ? (It should also be possible, later to make some "better" models, and the physics should then still be adequate)

A physics engine and a graphics engine are two completely different things. They are both abstract but have a unified way of dealing with objects. Matrices are the same, vectors are the same etc. And all a model is, is an accumulation of those math structures. So it does not matter which engine you choose, each one will support your models.

Quote:When i look at a tutorial of how to use Irrlicht with Newton Game Dynamics (http://gpwiki.org/index.php/Irrlicht:Physics), am i right when i thing that combining 3d-graphics and physics can be a various task, depending on the engines to be combined ? So, is it better to use a game engine, where this combination is already done?

For the most part, those two engines mentioned have a physics abstraction layer. What that is, is a unified way to use any physics engine you plug into it (be it ODE, PhysX, Newton, etc). Programming to an abstract interface will leave your code relatively change-free, when you switch to another physics engine. So, it is usually better to pick an engine and go with it because their goal is to provide an interface that will not change.

To quickly develop a 3D game, I'd use Panda 3D and Python. This thread might be interesting to you.