- Difficulty
- Intermediate
- Build time
- 60-90 min
- Estimated cost
- $0-$15
- Age range
- 11-17
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The moving block lifts a safe 100-gram classroom load through 10 cm with smooth rope travel and a clearly lower measured pull than a single fixed pulley.
Learning goals
- Identify how downward pull on the free rope end produces upward movement of a loaded block.
- Construct and explain a linear pull-to-slower linear lift system.
- Measure how the number of supporting rope segments changes performance.
- Diagnose losses caused by pulley bearing friction and rope bending.
Before you build
Materials, tools, and safety
Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult help recommended for sharp or heated tools.
Tools
- Ruler
- Removable tape for motion marks
Low-cost swaps
- Use equivalent brick-compatible parts from any kit.
- Use cardboard beams and straw bearings for a larger demonstration model.
- Use thread spools or smooth rings as low-load pulleys and a paper cup for the moving block.
Project-specific safety
- Keep fingers, hair, and loose sleeves clear of moving parts.
- Turn the mechanism by hand; do not attach a high-speed motor.
- Lift only small loads over a tray and never place hands or faces below a suspended mass.
Orient the build
Place the build so downward pull on the free rope end is on your left and upward movement of a loaded block 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
Build the overhead frame
Brace a wide stand taller than the planned 10 cm lift.
Test it with downward hand pressure before hanging anything.
Step 2
Assemble the fixed block
Mount two pulleys on independent low-friction axles at the top.
Keep their rope grooves aligned.
Step 3
Assemble the moving block
Mount two pulleys in a compact lower frame with a central load hook.
Balance the hook between pulley planes.
Builder checkpoint: After assemble the moving block, the first subassembly should stay aligned when handled gently.
Step 4
Anchor and thread rope
Secure one end to the fixed frame, then alternate moving and fixed pulleys.
Keep the rope uncrossed in every groove.
Watch for: If this stage binds or drifts, inspect frame flex before adding more parts.
Step 5
Mark input and output scales
Place rulers beside the free end and moving block.
Set both zero points with the load resting safely.
Step 6
Run an unloaded lift
Pull slowly through the full 10 cm output travel.
Correct any rubbing before adding mass.
Builder checkpoint: After run an unloaded lift, operate the build slowly and confirm that upward movement of a loaded block begins without binding.
Step 7
Measure the loaded pull
Add 100 grams and pull through a spring scale at constant speed.
Record peak and steady force.
Step 8
Compare a single pulley
Reroute through one fixed pulley with the same load and lift height.
Compare force and input distance.
Builder checkpoint: At the final checkpoint, The moving block lifts a safe 100-gram classroom load through 10 cm with smooth rope travel and a clearly lower measured pull than a single fixed pulley.
See the engineering
Why it works
- Input
- downward pull on the free rope end
- Output
- upward movement of a loaded block
- Motion
- linear pull-to-slower linear lift
- Energy losses
- pulley bearing friction, rope bending, side rubbing, frame flex
Why this works
Ideal mechanical advantage
If rope tension is similar in every segment, each segment supporting the moving block contributes upward force. The ideal mechanical advantage equals the number of supporting segments.
Look for: Count only rope segments that directly pull upward on the moving block, then compare pull and lift distances.
Where the energy goes
Efficiency and losses
The ideal model leaves out pulley bearing friction, rope bending, side rubbing, frame flex. 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 pulley bearing friction becomes visible or audible.
Math bite
Count supporting segments
Formula: ideal input force = load force / supporting segments
- 100 g load weighs about 0.98 N
- Supporting segments = 4
Substitute: input force = 0.98/4 = 0.245 N
Result: The ideal pull is about 0.25 newtons.
Input rope must move about four times the load distance.
Pulley and rope friction make real pull larger.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Lift the empty moving block through 10 cm at a slow rate.
Success looks like: Rope remains in every groove and the block rises without tilting.
Measure: Input force, input distance, and output distance.
Change: the number of supporting rope segments
Keep constant: load mass, rope, pulley set, lift height, and speed
- single fixed pulley
- two supporting segments
- four supporting segments
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The moving block tilts | Rope routing or load hook is off-center | Lift empty and compare both sides | Recenter hook and equalize rope paths |
| Pull force is unexpectedly high | A pulley binds or rope rubs a frame | Test each pulley separately | Realign axles and widen rope clearance |
| Rope leaves a groove | Pulleys are tilted or pulling angle is sideways | Watch entry while moving slowly | Align grooves and pull parallel to the block |
| The frame bends | The overhead beam lacks bracing | Apply load gradually and observe deflection | Add triangulation or reduce load |
Choose your tradeoff
Adding supporting segments lowers ideal force but increases rope length, friction, and setup complexity. Use free pulleys and straight rope runs before adding another stage.
Keep experimenting
Try another version
Two-segment lift
Use one fixed and one moving pulley.
Efficiency estimate
Compare ideal and measured force for each routing.
Powered drum
Add a ratchet winch to manage the longer input rope safely.
Build together
Classroom and access options
Classroom version
Teams can compare the number of supporting rope segments while keeping load mass, rope, pulley set, lift height, and speed. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Use high-contrast tape to distinguish input and output parts.
- Replace a small crank with a wider handle for an easier grip.
- Use thick cord, large pulley wheels, and high-contrast arrows showing the rope route.
Reflect on the design
- How did the number of supporting rope segments change the measured result?
- Where did pulley bearing friction affect the build most strongly?
- What evidence shows that ideal mechanical advantage explains the motion?
- Which change would improve upward movement of a loaded block without creating a new problem?
Glossary
- Ideal mechanical advantage
- If rope tension is similar in every segment, each segment supporting the moving block contributes upward force.
- Input
- The action or energy supplied to a system; here it is downward pull on the free rope end.
- Output
- The useful response produced by a system; here it is upward movement of a loaded block.
- 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
An original BrickLabClips interpretation of a standard mechanical mechanism.
- Mechanism verification: Standard kinematics were checked for motion direction, constraint, clearance, and likely friction points.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.
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