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Exploreum in Mobile has one.  there is a hard rubber disk at the  
bottom of the 'piston' tube, that both gives a seal to the  
compression stroke when the bowling ball lands, and to slightly  
cushion its fall.  (another at the top - see below re: jerking the  
rope).  we replaced the disk after about 5 years of very hard use.   
it was built by Hands-On...correct that, it was designed by Hands-on.

very very popular exhibit.

the connecting tube erich references, on ours, was the same size as  
the tennis ball tube.

outdoors, you might have a serious issue with the plex degrading in  
the sunlight.  and you definitely want to keep an eye on the rope  
attached to the bowling ball - it breaks and people will go boom on  
the floor.

one interesting observation i can add; to get the tennis ball to go  
higher, many, many of the visitors would jerk the rope as hard as  
they could, as if the more force they exerted on raising the bowling  
ball,  the higher the tennis ball would shooot.  Of course  since  
the  force of compressed air was only a funciton of how far the ball  
dropped, their extra effort did absolutely nothing.  you'd think it  
would be intuitive,  but it wasn't.
	




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