Engineering activity
Gear Train Builder
Make spinning gears from cardboard circles with notches! Spin one and watch the other spin too.
Materials and setup
- cardboard
- paper fasteners
- scissors
- markers
- ruler
How this changes by age
Pre-K (ages 3–4)
Make spinning gears from cardboard circles with notches! Spin one and watch the other spin too.
Steps
- Cut two circles from cardboard — one big and one small.
- Cut small V-shaped notches around the edges of both circles (parent helps with cutting).
- Pin each circle to a piece of cardboard with a paper fastener through the center.
- Push the circles together so the notches mesh like teeth.
- Spin the big circle. What happens to the small one? Does it spin the same way?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Discover that connected gears make each other spin
- Observe that meshed gears spin in opposite directions
- Practice fine motor skills with cutting and pinning
Kindergarten (ages 5–6)
Build a gear train with three cardboard gears. Discover how turning one gear makes the others move and how size affects speed.
Steps
- Cut three cardboard circles: small, medium, and large. Cut teeth notches around each edge.
- Pin all three to a cardboard base with paper fasteners, teeth meshing in a line.
- Mark a dot on each gear to track rotation.
- Turn the large gear one full rotation. How many times does the small gear spin?
- Draw arrows showing which direction each gear turns.
- Color your gears and label them: driver gear, middle gear, driven gear.
- Tell a grown-up one thing that surprised you.
Learning objectives
- Build a working gear train with three interlocking gears
- Observe that small gears spin faster when driven by large gears
- Track and record the direction and speed of gear rotation
Early elementary (ages 6–8)
Engineer gear systems that change speed and direction. Count teeth to predict gear ratios and verify with experiments.
Steps
- Cut gears with specific tooth counts: 8-tooth, 16-tooth, and 24-tooth (mark teeth with a pen).
- Pin gears to a cardboard base. Mesh the 8-tooth with the 24-tooth.
- Turn the 24-tooth gear once. Count how many times the 8-tooth gear spins. (Should be 3!)
- Calculate the gear ratio: big gear teeth / small gear teeth = speed multiplier.
- Try different pairings: 8-16, 16-24, 8-24. Record each gear ratio and actual spin count.
- Build a gear train that makes the final gear spin 6 times for every 1 turn of the driver.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Calculate gear ratios using tooth counts
- Predict output speed from gear ratios and verify experimentally
- Design a gear train to achieve a specific speed multiplication
Upper elementary (ages 8–10)
Design compound gear trains for specific speed and torque requirements. Calculate gear ratios, analyze the speed-torque trade-off, and build a functional mechanism.
Steps
- Research gear ratios and the speed-torque trade-off: speed up = less torque, slow down = more torque.
- Cut precision gears with 10, 20, 30, and 40 teeth. Mount on cardboard with paper fasteners.
- Build a 2-stage gear train. Calculate the compound ratio: (stage 1 ratio) x (stage 2 ratio).
- Challenge 1: design a gear train with a final ratio of exactly 4:1 speed increase.
- Challenge 2: design a gear train with a final ratio of exactly 4:1 torque increase (slow down).
- Test torque by hanging weights from a string wrapped around each gear. Which train lifts more weight?
- Write a report explaining when engineers choose speed gearing vs torque gearing in real machines.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Calculate compound gear ratios across multiple stages
- Analyze and demonstrate the speed-torque trade-off in gear systems
- Design gear trains to meet specific mechanical requirements
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
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