- Difficulty
- Intermediate
- Build time
- 55-85 min
- Estimated cost
- $0-$6
- Age range
- 10-17
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The marble completes a 1.5-metre route from a 40 cm drop in at least 10 seconds on four of five runs.
Learning goals
- Identify how release from a fixed 40 cm height produces a delayed but complete marble arrival.
- Construct and explain a gravitational descent-to-slow rolling motion system.
- Measure how one track slope or friction strip changes performance.
- Diagnose losses caused by rolling friction and wall rubbing.
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 paper strips and a large wooden ball when small marbles are not appropriate.
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 side, keep the route below shoulder height, and collect small balls immediately after testing.
Orient the build
Place the build so release from a fixed 40 cm height is on your left and a delayed but complete marble arrival 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 fixed limits
Mark a 40 cm start height and measure 1.5 m of track material.
Place the finish cup.
Step 2
Build the release gate
Use a sliding card that starts the marble without a push.
Practice three identical releases.
Step 3
Create a baseline slope
Connect the full path in one steady descent.
Time three runs before adding delays.
Builder checkpoint: After create a baseline slope, the first subassembly should stay aligned when handled gently.
Step 4
Add broad turns
Replace straight sections with supported switchbacks.
Keep every section slightly downhill.
Watch for: If this stage binds or drifts, inspect track deformation before adding more parts.
Step 5
Tune a friction zone
Add one removable strip of paper, felt, or tape texture.
Avoid anything that can trap the marble.
Step 6
Mark split points
Divide the path into equal thirds and label them.
Assign one timer or use video.
Builder checkpoint: After mark split points, operate the build slowly and confirm that a delayed but complete marble arrival begins without binding.
Step 7
Run five scored trials
Record total and split times plus any stop.
A stopped run does not qualify.
Step 8
Optimize one variable
Change one slope or friction zone and repeat.
Keep height, length, marble, and gate fixed.
Builder checkpoint: At the final checkpoint, The marble completes a 1.5-metre route from a 40 cm drop in at least 10 seconds on four of five runs.
See the engineering
Why it works
- Input
- release from a fixed 40 cm height
- Output
- a delayed but complete marble arrival
- Motion
- gravitational descent-to-slow rolling motion
- Energy losses
- rolling friction, wall rubbing, gentle impacts, track deformation
Why this works
Controlled energy dissipation
The marble must lose gravitational energy gradually through rolling friction and redirection. Abrupt obstacles can slow it, but they also increase random stops and rebounds.
Look for: Record split times for thirds of the track and locate where most delay occurs.
Where the energy goes
Efficiency and losses
The ideal model leaves out rolling friction, wall rubbing, gentle impacts, track deformation. 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
Calculate average speed
Formula: average speed = path length / time
- Path length = 1.5 m
- Time = 12 s
Substitute: speed = 1.5 / 12 = 0.125 m/s
Result: The marble averages 0.125 metres per second along the track.
Local speed changes from section to section.
Path length and hand timing are approximate.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Time three runs on a steady-slope baseline.
Success looks like: Four of five scored runs finish in at least 10 seconds without stopping.
Measure: Total time, split times, stops, and wall contacts.
Change: one track slope or friction strip
Keep constant: height, path length, marble, release, catch, and room
- baseline
- lower middle slope
- added removable friction strip
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The marble stops | A section is level or friction too high | Nudge it and mark the exact point | Increase local drop or reduce roughness |
| It becomes fast near the end | Too much height remains late | Compare split times | Flatten the final third and spend height earlier |
| Times vary | Release or track flex changes | Film the gate and supports | Stiffen the route and standardize release |
| It falls out on turns | Entry speed is high or walls low | Watch from above | Widen, bank, and raise the outside edge |
Choose your tradeoff
Aim for slow motion in every section, not one dramatic delay. Increasing friction can lengthen time, but the reliability penalty grows quickly near the point of stopping.
Keep experimenting
Try another version
Eight-second target
Use a 1-metre route.
Fifteen-second target
Reach four of five reliable runs.
Section model
Predict total time by summing average split times.
Build together
Classroom and access options
Classroom version
Teams can compare one track slope or friction strip while keeping height, path length, marble, release, catch, and room. 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 an oversized track, tactile split markers, and roles for release, timing, spotting, and recording.
Reflect on the design
- How did one track slope or friction strip change the measured result?
- Where did rolling friction affect the build most strongly?
- What evidence shows that controlled energy dissipation explains the motion?
- Which change would improve a delayed but complete marble arrival without creating a new problem?
Glossary
- Controlled energy dissipation
- The marble must lose gravitational energy gradually through rolling friction and redirection.
- Input
- The action or energy supplied to a system; here it is release from a fixed 40 cm height.
- Output
- The useful response produced by a system; here it is a delayed but complete marble arrival.
- 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.