Can the tiny fast output start the same heavy crate as the big slow output?
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See it another way
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.
After you watchCan the tiny fast output start the same heavy crate as the big slow output?
The short answer
Where two gears mesh, their teeth pass the contact point in matched one-for-one steps. That makes turning speed depend on tooth count: for the same driver motion, an output gear with fewer teeth completes more turns, while one with more teeth completes fewer. A gear train cannot create energy; the story's matched load test reveals how that limit appears when the outputs face the same resisting crate.
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
At the mesh point, one tooth passing on the driver forces one tooth to pass on the output. A fixed 18-tooth driver therefore sends 18 teeth through the contact each turn. A 6-tooth output must circle three times to pass those 18 teeth, an 18-tooth output circles once, and a 36-tooth output circles half a turn. The tooth ratio predicts speed exactly. To test something speed alone does not show, the interactive story adds equal spools and equal loads only after the reader predicts an outcome.
What people get wrong
A quickly spinning output can look like a free machine upgrade, but gears have no hidden energy source. Tooth count can rearrange how an input appears at the output; it cannot make the total input grow. The fair way to find what that means for a resisting load is to use equal-size crank handles, apply equal effort, keep the spool and crate matched, and change only the output gear.
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
- Before the load test, ask which facts the child knows from the speed toys and which property has not been measured yet.
- At the prediction page, treat fast, slow, and together as serious models. Ask for a reason before applying the same push to both equal-size cranks.
- After the reveal, ask why equal spools and equal crates made the comparison fair.
For grown-ups
For two ideal external gears, equal tangential speed at the pitch point gives omega2/omega1 = N1/N2. The story establishes that unloaded speed relation before the gate, then withholds the paired rotational-load result for a source-bound prediction experiment. Equal hand effort through equal-size crank handles supplies equal input torque, while equal spool radii isolate the gear-ratio variable. The post-gate explanation introduces torque, stall, and ideal power conservation; real efficiency remains below one.