How do a gear and its rope drum work together to lift a crate?
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O Wow Moment: What's a Gear to Do?
See a museum gear-up and gear-down test compare speed with lifting effort, making the same speed-for-force trade visible with real LEGO gears.
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What else makes you wonder?
Why are real gear teeth curved instead of square?
A tooth shape can change how smoothly contact moves from one pair of teeth to the next.
What changes when a third gear sits in the middle?
Track both the tooth ratio and the number of direction reversals separately.
What happens when ten gear pairs are chained together?
Ratios multiply, but tiny friction losses also collect at every mesh and bearing.
More to explore
After you watchHow do a gear and its rope drum work together to lift a crate?
The short answer
Gears trade turning speed for axle twist. At their shared contact, equal tooth traffic sets the speed ratio, while the same contact push acts at different distances from the axles. A lifting machine also has a rope drum: a wider drum winds more rope per turn and makes the load resist with more twist.
Try this next
- What if both gears had 18 teeth? Predict the output turns for one crank turn, then set the speed-ratio toy to the matching middle state.
- What if the output had 9 teeth? Use tooth traffic: an 18-tooth driver sends 18 teeth past the contact. Predict how many 9-tooth loops the output needs.
- What if an idler sat between the driver and output? Count direction reversals separately from tooth ratios. Predict which feature changes and which stays set by the first and last gears.
Now you — bend it
- What if Keep the driver at 18 teeth and choose a 9-tooth output.Count how many complete 9-tooth loops are needed to pass the driver's 18 teeth through the mesh.
- What if Add one same-size idler between the 18-tooth driver and 6-tooth output.Track the number of direction flips and the final tooth ratio as two different questions.
- What if Imagine each of ten gear meshes passes on 97 percent of the power it receives.Losses compound: the useful fraction is 0.97 multiplied by itself once for each mesh.
Can you prove it?The output turn ratio equals driver teeth divided by output teeth. — Use the speed-only toys to test 6, 18, and 36 output teeth against the fixed 18-tooth driver. The expected output turns are 3, 1, and one half per driver turn.
Design your own test:Choose an output tooth count and predict its turns per crank by dividing 18 by that count before checking a model.
Explain it to a 6-year-old: At the touching spot, both gears pass the same teeth, so a little gear loops around more times than a big one.
The whole story
How it works
An 18-tooth driver makes a 6-tooth output turn three times, an 18-tooth output once, and a 36-tooth output half a turn. A general lever toy shows why the same push farther from an axle gives more twist. The story then combines a gear-size change with a drum-size change and asks the reader to predict the whole machine.
What people get wrong
A gear that supplies more axle twist does not settle the pull at the end of a rope. The rope drum radius matters too. Compare the entire path from hand crank to crate.
The catch
Ideal gear equations ignore losses. Real teeth rub and flex, bearings drag, and some input becomes heat and sound, so a real train delivers less output power than it receives. Gear size, tooth strength, alignment, lubrication, and spool radius also matter in a practical lifting machine.
Questions kids ask
Why does a smaller output gear spin more times?
The same number of teeth must pass the shared contact on both gears. A smaller gear has fewer teeth around one loop, so it must complete more loops to pass the same tooth total.
How do you calculate the output speed?
Divide the driver tooth count by the output tooth count. An 18-tooth driver turning a 6-tooth output gives 18 divided by 6, or three output turns for every driver turn.
Can a gear train create extra power?
No. Gears have no energy source. An ideal train only redistributes the input, while a real train also loses some energy to friction, flexing, sound, and bearing drag.
What does a middle idler gear change?
An idler can reverse the final rotation direction or bridge a gap. By itself, it does not change the speed ratio set by the first and last gears.
Talk about it
- Ask how the same push changes its twisting effect when it acts farther from an axle.
- At the gate, ask what changed in the gear and what changed in the rope drum.
- After the reveal, ask why gear size alone did not predict rope pull.
For grown-ups
For ideal external gears, angular speed scales as the inverse tooth ratio and torque as the tooth ratio. Rope pull then equals output torque divided by drum radius. The gated experiment tests composition of these two relations with matched input handles and equal crates. Real efficiency is lower than one.