Count passing teeth
A smaller gear must turn farther to pass the same number of teeth.
Gear Factory
Mesh gears to compare tooth counts, rotation direction and output turns.
Grades 3–5 · Physics
Your goal
Make the output turn about 0.50 times counterclockwise while the driver turns 1 times clockwise. Use a tooth ratio of 12 to 24.
Reduced motion is on. The controls still update the scene.
Driver made 0 clockwise turns. Output made 0.00 counterclockwise turns. Each output turn requires 24 teeth to pass the mesh.
Each click records one complete clockwise driver turn. White rim markers show the resulting orientation. Ideal rigid gears have matching tooth spacing and no slipping. The purple idler has 12 teeth.
Related resources
Study as flashcards
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Learn with Gear Factory
Gear Factory gives elementary learners a workshop for exploring connected rotation. Choose the tooth counts of a driver and an output gear, add or remove an idler, and turn the driver through complete revolutions. The illustrated gears and turn counter help children connect a smaller tooth count with faster turning. Each mesh reverses the direction of rotation, so an idler changes direction while leaving the overall speed ratio unchanged. Guided goals ask students to predict output turns and test their reasoning with different gear combinations.
What to look for
Track each mesh
Each pair of external meshing gears turns in opposite directions.
Try an idler
An extra gear reverses direction again without changing the overall speed ratio.
For teachers and curious learners
Use tooth ratios and meshing directions to predict gear motion. Ask students to predict what will happen, change one setting, and explain what they observe. Learn gives a starting point. Practice and Challenge offer new goals with the same scene.
Ideal rigid gears use matching tooth spacing with no slipping. An optional 12 tooth idler changes the final direction without changing the overall tooth ratio.