Here's a silly but fun thing you can do this summer when you are really bored. Tennis ball cannons are frequently referred to as a tennis ball launcher or a Polish cannon. Although tennis ball launchers are a little different when it comes to function, like run and fetch with your dog, they more or less have the same role, shooting tennis balls into the air.  Tennis ball cannons can generally be made with homemade materials or parts that can be found around the house. Most people use or build them for fun at the park or simply playing games with others who have them.  However, as a word of advice to those wanting to build one, it can injure you.  Even if you build a canon correctly and use it correctly, it can still injure you.

Here are some safety tips once you have built a tennis ball cannon:

 * Employ common sense. Do not use it if you're not an adult.
* Treat the finished cannon as if it were a gun, and always point it in a safe direction.
* Act responsibly.

Components of a Tennis Ball Cannon

* Duct tape

* 6 tin cans, 2 5/8" diameter, 5 1/2" tall
* 1 tin can, 2 5/8" diameter, 3 1/8" tall
* Lighter or matches
* Lighter fluid
* can opener, one that can cut the rounded ends of the can
* can opener, one that can punch a hole on a can
* Tennis ball

Final dimensions of tennis ball cannon are 33 1/8" tall, and 2 5/8" in diameter. Getting the right tin cans for the tennis ball cannon is vital.  The key factor is that the diameter of the cans must be 2 5/8", so be sure you measure the cans to use before you buy them. A 15 ounce can of Green Giant Asparagus Spears that is 5 1/2" tall and is exactly 2 5/8" in diameter, so it is what you should be searching for.  If you find shorter than 5 1/2" tall that's acceptable but it is easier to use longer ones as you'll need fewer cans.  These cans need to have flat bottom and top, and not rounded ones, so that you can remove them with a can opener.

How to put it together

1.  Using the first type of can opener, cut off the top and the bottom of the six large cans, so that each one ends up looking like a small tube with no top or bottom.
2.  With the other type of can opener, take the small can and poke 6 holes in the top. The top will look like a grill with those little triangle-shaped holes.  This is the only way you have to open the can, so you have to strongly shake the contents out.  Do not remove the bottom of the can.
3.   On the side of the small can near the bottom, just about an inch from the bottom, poke a hole about 1/8" in diameter.  This hole will be used for pumping in the lighter fluid.
4.   With the small can at the bottom and its grill-like end facing on top, use the duct tape to connect all the cans together end to end making a barrel, but make sure that the grill-like end is inside the cannon and you'll only be able to see it when you look down the barrel of the cannon.  The bottom must be solid and not cut at all.  Once all the cans have been joined and taped securely, wrap two to three layers of duct tape starting from above the lighter fluid hole, going all the way to the end of the cannon but take care not to cover the hole.  Don't be afraid of adding two or three extra layers more if you feel that your duct tape won't hold (will melt or get loose) from the heat when you fire the cannon.

Instructions for use

Before you progress to firing the tennis ball cannon, be sure you read and understand all these instructions first.
1. Hold the tennis ball cannon vertically, and then squeeze about a half ounce of lighter fluid into the hole.
2. Hold the tennis ball cannon upside down with your right hand, waving it in large sweeping motion for about six or seven times to get the lighter fluid to distribute throughout the tennis ball cannon.  Don't worry if a few drops of fluid come out to the end during your waving motion.
3. Place a tennis ball in the end of the cannon and push it down with your hand as far as the bottom of the top can.
4. Aim the tennis ball cannon in a safe direction, pointing straight up.
5. Hold a lit lighter up to the small hole in the bottom can, this flame would cause the lighter fluid fumes to swell, producing great pressure to shoot the ball out the end.

Again, tennis ball cannon should be used responsibly and sensibly. No matter if it is used for fun at the park or showing off for some friends, make sure you play it safe.