Apologies if this is a FAQ, I didn't see any references to "disabled"
and "physics" in the mailing list archive.

I just started gazebo with physics disabled by virtue of copying the
empty_worlds.launch and adding -p to the arguments.  Then I started
the pr2 simulator (roslaunch pr2_gazebo pr2.launch) and pr2_teleop.
When I do that and try to drive the robot around, it doesn't move.

Is this expected behavior or am I missing something.

It would not be terribly surprising to me to learn that if the laws of
physics were all repealed we wouldn't be able to get anywhere :-)

--wpd