We just learned about the Air Gap in a motor.
Another type of thing used in machines is the Rack and Pinion.
A pinion is a gear, which we learned is a circle with teeth on the end.
The rack is a long flat line that has teeth on it, that match up with the gear.
When the gear spins around, it goes along the rack one way or the other.
These can be used as pinion wheels for something like a train that goes along a rack track, or sometimes as a pinion wheel that climbs up and down a pole that has a rack on it.
(from: wikipedia - rack and pinion)
Kid Facts - Blast from the past: Shock Diamond
