Subject: How can I create a tennis ball launcher using propellants?

The assignment is to create a tennis ball launcher that is inexpensive.  I 
have never done anything of this sort, and was hoping that you could get 
me started with some ideas.  I would like to be able to use propellents in 
my project.  If you think this is possible, what propellents should I use?
Where can I get these materials?  If you cannot give me this information, 
I would greatly appreciate it if you could give me the names of some web 
sites that would be helpful. Thank you.  

Re: How can I create a tennis ball launcher using propellants?