Science Buddies: "Ask an Expert"

I tutor a 4th grader who needs to build a roller coaster in a shoebox. The goal is to keep a marble on tyhe ramp for the longets time without getting stuck or falling off. Any suggestions?

Hmmm... well, there are several routes one could go, but the trick would seem to be to have the shallowest possible slope that the marble will reliably continue to move on. Anything buildable by a 4th grader that depends on building up a lot of speed going down and then coming back up is likely to be too unreliable, I would think.