A marble run is one of those STEM projects where the process is as engaging as the goal. Children do not just want to build a run that works — they want to watch the marble travel through every twist and turn, to hear it clink against each element, and to extend the run further and further until the marble's journey becomes an epic adventure. The physics is real: gravity, friction, momentum, and energy transfer are all on display in every run.

Building Materials

• Cardboard tubes (paper towel, wrapping paper) cut in half lengthwise as channels.
• Foam pipe insulation cut lengthwise (excellent marble channels, available at hardware stores).
• A cardboard box or foam board as the vertical mounting surface.
• Tape to mount channels at angles.
• Marbles or small balls.

Design Process

1. Plan on paper: sketch the path the marble will take.
2. Start at the top: mount the first channel at a gentle downward angle.
3. At the end of the first channel, add a second channel (angled the other way) to catch the marble and redirect it.
4. Continue alternating direction down the board.
5. Test after each channel is added — don't wait until the whole run is built to find the first problem.

Frequently Asked Questions

Why does my marble stop in the middle of the run?

A marble stops when it loses enough momentum to overcome friction — usually at a transition point between channels. The most common cause is the angle being too gentle (not steep enough to maintain speed) or a gap between channels where the marble loses energy. Steepen the problem channel slightly, ensure the marble lands at the start of the next channel rather than the side, and check that there are no gaps where the marble can escape. Small adjustments — a few degrees of angle — often make the difference.

Related science: Marble Maze | Roll Balls Down Ramps | Paper Bridge