Grounding in buildings
When I'm standing in my room on the 10th floor, is my body at the same voltage potential as the ground pin? I don't think this is the case, because the ground wire doesn't make contact with the floor I'm standing


A building has usually rather low ground resistance. Think of all the plumbing and other metal structures, for example.


  So probably the 10th floor is at 110V and the ground pin is at 0V, and when I touch the ground pin I get a shock. 


If the ground resistance is (unusually) high, you won't get a lethal shock, because there will be no current flow. Note that you may get a small shock from your own electrostatic discharge, but that is not dangerous.