What exactly is a physics engine?

[RealmSeeker]

Is a physics engine only collision detection and apply some forces or is there more to it?

EDIT: fixed typos

[chaosavy]

there is a bit more to it depending on the engine, some will have character controllers. What a character controler is basically a representation of a walking "being" so it can go up stairs and up slopes, etc. Also some will have vehicle representations, different types of objects (some that when colliding with other objects will cause "apply some forces" some that won't). Also physics engines tend to have ray scene queries. They also tend to have hinges and joints.

[RealmSeeker]

Think it will mean I have to check it out myself.

What engine would be suggestable for:
- characters
- carrages (e.g. with horses)
- boats/water
- flying object e.g. planelike objects

[spacegaier]

As already mentioned it highly depends on the engine, but some also support the physical correct simulation of fluids or cloth.

E.g. have a look at the PhysX features to get an idea of what big physics engines are capable of: http://developer.nvidia.com/object/physx_features.html

[RealmSeeker]

If you take use of a physics engine, it looks like to start with it as soon as possible as I know class structures in general already.

Or would people advice, fool around with only the OGRE first and later implement physics into it/start over?

[chaosavy]

I did Ogre only for quite some time at first then moved onto using phyisics once I got to the point of wanting my objects not to fly through each other