Materials: wooden dowels, wood glue, tape, magnets, ball bearings.
1. Take two wooden dowels, squeeze them together with bricks on each side, and put wood glue in the middle in the inner seam.
2. Tape some square neodymium magnets down the middle along the wooden dowels. How many you put and the spacing is up to you.
3. Place the ball bearings down the line, putting as many or as little as you want.
4. Toss a ball bearing on the first magnet station and it will move each ball bearing down the line, and there will be a small energy build up.
5. It doesn't work very well as it didn't shoot very powerfully with 4 magnet stations, so keep that in mind if you try to make this.