How can I make objects behave as if they were solid? If I start blender, I see the default scene, with a cube, a lamb, and a camera. If I add a new cube, and the cursor is in or near the center, it goes on top of the original cube, or floats around roughly where the original cube is located, passing through it as if neither object were really solid.

But say I want to make the cubes behave as if they were both solid? How can I make blender treat objects as if they were solid?
You can turn your objects into rigid bodies.



If two rigid bodies are on the same place they will push away form each other.

In this example a cube and a sphere are on the same place. This is what happens when you hit AltA to start a simulation: The cube gets pushed away... (a plane is there to catch them as a rigid body, but passive type)