This is an apparatus for a high school physics class used when helping students develop a model for uniform acceleration. When we do the lab we play a metronome and students mark the position at one or two second intervals. They create a position vs. time graph and get a really nice quadratic relationship.
I printed in ABS with 10% infill and 0.27 mm layer height. I had to do some cleanup of the center on the side facing the build platform. Once cleaned up I used super glue to affix a cone to each side.
For the rails we used electrical conduit from Lowes. It comes in 5 foot sections. The rails are held in position using bricks. It is important to note that if the incline is too steep the apparatus will slide rather than roll resulting in bad data. I suppose the data are not bad per se, but they would not reflect uniform acceleration.
Check out this blog post for a little more detail on the lab.
UPDATE: This can be greatly enhanced by coating the cones in Plastidip. The increased friction removes all sliding even for very steep inclines.