This is just a small-scale version of a magnetic rail gun. it moves a set of connected magnets across electrically charged rails. If you had larger magnets and a higher voltage it could bend the connecting bar and be somewhat like a cannon.
wire coat hanger
9 volt battery
2 disk magnets
Cut your cardboard about 6 inches wide, and 10 inches long. Then glue 2 strips of foil to the cardboard long ways, but not touching. leave about 2 inches hanging of the end of your cardboard.
Now, take the 2 wires and attach one end each to the battery using tape. Then take the other free ends and tape them to the ends of the foil.
Take your coat hanger and cut a pice that reaches about to the middle of the foil strips, mine is about 3 inches. Now you have to make the ends flat so the magnets will be strait. i used a hammer, but it is probably better to file them down.
Take the magnets and attach them to the ends of the wire. The polarity has to be facing opposite directions.
Step 4: Finished!!
Set the magnet rail thingy on the foil and it magically moves! if it goes the wrong direction, just start it at the other end. If you don't think its going fast enough, it can be fixed by higher voltage, but don't, it won't be my fault if you hurt yourself. use common scence