Here's an easy to make ping pong ball launcher that you can build from stuff you may have laying around your house. It will easily fire ping pong balls over 25 feet.

Step 1: Gather Your Resources

You'll need:

A toilet paper roll tube
Ping pong ball(s)
Two paper clips
Two rubber bands
Small plyers
3/4" clay marble (made from something like Sculpey clay) or a wooden ball.

Step 2: Bend the Paper Clips

Straighten the paper clips into this shape.

Step 3: Mark the Tube

Lay the straightened paper clips on the tube near the edges like this. You want them close to the edges so they keep the ping pong ball from slipping out, but wide enough apart that the striker ball won't hit them.

Use a pencil to draw a line where the paper clips touch the tube.

Step 4: Poke the Holes

Poke four holes about 1/2 inch from the end of the tube on each of the lines you marked in the previous step.

Step 5: Insert the Paper Clips

Insert the two paper clips into the holes you created.

Step 6: Drill the Hole

Using utmost security precautions, drill a 1/8 inch hole through your clay marble/wooden ball.

Step 7: Build the Striker

Loop the two rubber bands as shown so they are knotted together. Next push the rubber band through the clay marble/wooden ball until the rubber band knot is jammed in the middle of the ball.