Put a 12 and a 36 on the board (4 holes apart). Clip a flag on each. Put the crank on the 12.

Now swap: crank the 36 once. How many times does the 12 turn? ______ Which one is faster? ______

Turn the first gear clockwise ↻. Draw an arrow on every other gear to show which way it spins. Then build it and check!

Find the rule: with an odd number of gears the last one turns ________; with an even number it turns ________.

Crank the driver once and count how many turns the follower makes.

What do you notice about the last two columns? ________________________________

Engineers call this the gear ratio. Bicycles, clocks and mixers all use it.

1. Build the fastest machine you can: one crank turn should spin the last gear as many times as possible. Explorer kit: use a double gear!
2. Draw your machine below and write how many turns you counted.
3. Build the slowest machine. Which one is easier to turn?

Gear hunt at home: where are gears hiding? (bicycle, clock, mixer, toy car …) ________________________