Science Buddies: "Ask an Expert"

I am having trouble with the spring that goes into my Launch machine.
It is a dowl, with a washer at one end, and a 20 Newton spring, which goe into the PVC pipe and then a string at the end, pulled out of the end of the PVC which has a closure with a hole drilled large enough for the dowl to move back, and launch.
problem: it is not launching a ball bearing very far, only a foot? What am I doing wrong?

Hello and welcome to the forums!

I'm sorry to say, that without more information it's hard to diagnose a problem like this. Any chance you could post a diagram? Here are some basic questions.
1. Does the ball bearing fit snugly in the PVC pipe? If it's very loose, you will lose a lot of energy when it's fired. If it's too tight, friction will rob you of a lot of the force. Also, how long does the ball bearing travel through the pipe?
2. How does the mass of the ball bearing compare to the spring constant?
3. How far are you able to compress the spring?
Any more things you can think of to tell us will help.
Keith