Gears: the gear ratio

What the experiment shows

A motor turns the small gear. The big one meshed with it turns half as fast and in the other direction — this is how gearboxes work.

How to run it

1. Run the example and compare how the gears turn.
2. Count the turns: how many turns of the small gear make one turn of the big one?
3. In the editor change the ratio in the “Transmission” panel — for example to −1.

Questions to discuss

• Why do the gears turn in opposite directions?
• For lifting a load, is a big or a small gear on the output better?

The science

The teeth of both gears move at the same speed, so the angular speeds are inversely proportional to the tooth counts: ω₂/ω₁ = −z₁/z₂ = −12/24. What we gain in speed we lose in force: the big gear is slower but delivers more torque.

Try it at home

Look at the gears on a bicycle: which sprocket makes it easier to go uphill? Or make two cardboard gears with paper-clip teeth.

What to change in the editor

• Draw your own gear with “Sketch → Extrude”.
• Add a third gear.