How do gears work?
Gears are wheels with teeth that push each other round. When the teeth of two gears mesh, turning one gear turns the other. The teeth must fit together exactly — so gears go at just the right distance apart. Look closely: meshing gears always spin in opposite directions!
Try Gear Friends for freeComplete MightyCog booklet collection: 82 PDF booklets for $12.99. Instructions only; individual booklets remain free.
Explore the printable packTry it yourself
Turn one gear clockwise. Which way does its neighbour go?
Build it: 11 builds that teach gears
- ⚙️ Gear Friends: Three gears holding hands — spin one and they all dance. (level 1 of 5, about 8 minutes, 6 steps)
- 🌀 Propeller Push Car: Push the car and the propellers on its back spin three times faster than the wheels! (level 1 of 5, about 12 minutes, 8 steps)
- 🔢 Odometer Cart: Five turns of the wheels make the flag go round just once — a cart that counts! (level 1 of 5, about 15 minutes, 9 steps)
- 🎠 Idler Parade Car: A parade of gears rides on top — each one spins the opposite way to its neighbour! (level 1 of 5, about 20 minutes, 13 steps)
- 🌉 Speed-Cancelling Gear Bridge: A 40–8–40 gear train: the middle turns five times, but the ends stay together. (level 2 of 5, about 15 minutes, 5 steps)
- 🔀 Dual Output Gear Bench: One central input drives two unequal outputs: count each branch independently. (level 2 of 5, about 20 minutes, 14 steps)
🧪 Gear Speed Lab: Two cranks, two gear pairs: one makes things FAST, one makes things STRONG. (level 2 of 5, about 20 minutes, 13 steps)- 🔬 Compound Counting Bench: Two five-to-one stages multiply: count 25 input turns for one output turn. (level 2 of 5, about 20 minutes, 7 steps)
- 🌪️ Ripcord Top Launcher: Pull a toothed rack and watch two gear stages turn the top. (level 2 of 5, about 20 minutes, 18 steps)
- 📏 Rack Travel Bench: Turn a small gear and measure the straight travel of a captured rack. (level 3 of 5, about 25 minutes, 13 steps)
- ⏯️ Geneva Step Counter: Turn the handle smoothly — the pointer moves in jumps: click… wait… click! (level 3 of 5, about 30 minutes, 9 steps)
In the classroom
- E2 Turning Things (Explorers, Foundation)
- E4 Swing & Rhythm (Explorers, Foundation)
- I9 Signals & Remote Control (Inventors, Intermediate)
Common engineering questions
How can I try gears at home?
Turn one gear clockwise. Which way does its neighbour go?
Which builds teach gears?
11 MightyCog builds teach it: Gear Friends, Propeller Push Car, Odometer Cart, Idler Parade Car and Speed-Cancelling Gear Bridge and more. Start with Gear Friends: 6 steps, about 8 minutes.