- Difficulty
- Beginner
- Build time
- 45-75 min
- Estimated cost
- $0-$6
- Age range
- 10-16
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The marble completes a route at least 1.5 metres long and reaches the catch cup on four of five releases.
Learning goals
- Identify how release from a fixed starting height produces controlled marble arrival in a target cup.
- Construct and explain a gravitational descent-to-guided rolling system.
- Measure how one track slope changes performance.
- Diagnose losses caused by rolling friction and joint impacts.
Before you build
Materials, tools, and safety
Reuse-material cost: $0-$3 with reused materials. Supervision: Adult help recommended for sharp or heated tools.
Tools
- Ruler
- Pencil
- Scissors
- Timer or phone stopwatch
Low-cost swaps
- Use reclaimed paper and packaging while keeping material limits equal for every team.
- Replace metal test weights with labeled bags of coins or washers.
- Use folded cardstock channels and a large wooden ball when small marbles are unsuitable.
Project-specific safety
- Keep load and drop tests below shoulder height and away from faces.
- Clear the test zone before releasing moving objects or suspended loads.
- Contain every edge, keep the run below shoulder height, and store marbles away from young children after testing.
Orient the build
Place the build so release from a fixed starting height is on your left and controlled marble arrival in a target cup is on your right. Call the side facing you the front, the far side the back, the tabletop the bottom, and the opposite face the top.
Build it
Step-by-step instructions
Step 1
Set the constraints
Mark start, finish, 1.5-metre minimum path, and maximum 60 cm drop.
Place the catch cup first.
Step 2
Build the start gate
Make a card slider that releases without pushing.
Test it on one short straight track.
Step 3
Add the first slope
Tape a shallow channel and support its midpoint.
Roll once and watch for twisting.
Builder checkpoint: After add the first slope, the first subassembly should stay aligned when handled gently.
Step 4
Build a broad turn
Overlap two channels and raise the outside wall.
Keep the joint smooth in the travel direction.
Watch for: If this stage binds or drifts, inspect wall contact before adding more parts.
Step 5
Add a controlled drop
Limit vertical drop to 10 cm and build a receiving funnel.
Contain every side.
Step 6
Connect to the finish
Use the remaining height gradually and align the last track with the cup.
Pad the landing.
Builder checkpoint: After connect to the finish, operate the build slowly and confirm that controlled marble arrival in a target cup begins without binding.
Step 7
Run five trials
Reset only the marble and release gate.
Record the first failure location.
Step 8
Tune the weakest point
Change one slope, wall, or joint and repeat five trials.
Keep the rest of the route fixed.
Builder checkpoint: At the final checkpoint, The marble completes a route at least 1.5 metres long and reaches the catch cup on four of five releases.
See the engineering
Why it works
- Input
- release from a fixed starting height
- Output
- controlled marble arrival in a target cup
- Motion
- gravitational descent-to-guided rolling
- Energy losses
- rolling friction, joint impacts, track flex, wall contact
Why this works
Energy management on a track
Height gives the marble gravitational potential energy. Track slope and turns decide where that energy becomes speed and where friction or impacts remove it.
Look for: Mark three checkpoints and note where the marble is fastest, slowest, or most likely to leave the track.
Where the energy goes
Efficiency and losses
The ideal model leaves out rolling friction, joint impacts, track flex, wall contact. These effects turn some input energy into heat, sound, vibration, or unwanted motion, so measured performance will be lower than an ideal calculation.
Look for: Run the build slowly and locate the first place where rolling friction becomes visible or audible.
Math bite
Find completion reliability
Formula: reliability = successful runs / total runs × 100%
- Successful runs = 4
- Total runs = 5
Substitute: reliability = 4 / 5 × 100% = 80%
Result: The run is 80 percent reliable in this test.
More trials give stronger evidence.
A changed release or damaged track affects results.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Roll through each new section at low speed before connecting the full route.
Success looks like: Four of five complete releases reach the catch cup.
Measure: Completion, travel time, derailment point, and wall contacts.
Change: one track slope
Keep constant: marble, route, start height, gate, supports, and catch cup
- baseline slope
- 2 cm lower
- 2 cm higher
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The marble stops at a joint | An overlap faces the wrong way or rises | Roll slowly by hand | Tape the upstream section over the downstream section |
| It flies off a turn | Speed is high or outside wall low | Watch from above | Flatten the entry and raise the wall |
| The route changes between runs | Supports flex or tape lifts | Press gently at each support | Brace and retape |
| The marble misses the cup | Final alignment is off | Run only the last section | Widen the funnel and center the outlet |
Choose your tradeoff
Repair the earliest unreliable section first. Steeper slopes overcome friction but increase impact speed, so distribute height rather than spending it all at the start.
Keep experimenting
Try another version
Three-section run
Use one slope, one turn, and a cup.
Ten-run reliability
Reach nine successful runs out of ten.
Sound checkpoints
Add safe paper tabs that make different sounds.
Build together
Classroom and access options
Classroom version
Teams can compare one track slope while keeping marble, route, start height, gate, supports, and catch cup. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Assign varied roles such as designer, builder, tester, recorder, and presenter.
- Provide pre-measured materials and a visual checklist when helpful.
- Use a larger ball, 6 cm-wide tracks, tactile checkpoint labels, and team roles for release and observation.
Reflect on the design
- How did one track slope change the measured result?
- Where did rolling friction affect the build most strongly?
- What evidence shows that energy management on a track explains the motion?
- Which change would improve controlled marble arrival in a target cup without creating a new problem?
Glossary
- Energy management on a track
- Height gives the marble gravitational potential energy.
- Input
- The action or energy supplied to a system; here it is release from a fixed starting height.
- Output
- The useful response produced by a system; here it is controlled marble arrival in a target cup.
- Efficiency
- The fraction of input energy that becomes useful output instead of friction, sound, heat, or unwanted motion.
Build your dreams
One build can start the next.
Share what you learned, change one variable, and help another builder understand what worked.
Explore more guidesSources and build notes
A common classroom engineering challenge implemented with original constraints, diagrams, and measurement guidance.
- Classroom challenge basis: A controlled-variable engineering activity with original constraints, scoring ideas, and measurement guidance.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.