Here I will describe a cannon that can drive ping pong balls fast enough to go through plywood and aluminum cans. This "vacuum cannon" has been demonstrated in college physics classes, since it involves many basic physics concepts such as Newton's laws of motion, air pressure, and particle dynamics. There are some great videos online of these college class demonstrations, but details of construction are a bit sketchy. Some sources claim achieving a ping pong ball speed well over the speed of sound (340 m/s, or 760 mph), but others perform a mathematical analysis that indicates a limiting speed of about 280 m/s ( 625 mph). I made a ballistic pendulum and conducted many speed measurement tests, my average speed was 378 m/s (845 mph). So I am going to claim supersonic speed, and admit there is some controversy.
So here is the warning: At this speed, even a ping pong ball is very dangerous. We are talking about a projectile travelling as fast as rifle bullets. If you elect to build this device, you must treat it with respect and use appropriate safety measures. These include:
Set it up so nobody can be in front or behind the cannon.
Wear safety glasses and eye protection.
Do not put any part of your body in front of or behind the cannon.
Also - the cannon can and will fire at unexpected times, especially as you experiment at the beginning.