To much air would get past the ping pong ball, so it wouldn't move fast enough.
Originally Posted by kls-ccc
The pipe needs to be enough bigger than the ball that a little air will get past it, but not so much bigger that to much of the air goes around it.
Visualize it as blowing a ping pong ball down a pipe with 14.7 psi of air pressure.
The ping pong ball will go much faster down a pipe that has an inner diameter just slightly larger than the ball than it will down a larger pipe.
If more government is the answer, then it's a really stupid question.