Gears are wheels with teeth that slot together. When one gear is turned the other turns as well. If the gears are of different sizes, they can be used to increase the power of a turning force. The smaller wheel turns more quickly but with less force, while the bigger one turns more slowly with more force. Cars and bicycles use gears to achieve amazing speeds our bodies could never match without help.
The neat thing about gears is that they move in opposite directions. In other words, when one gear turns to the right (clockwise), the gear attached to it will turn to the left (counterclockwise). This pattern continues to repeat, regardless of how many gears are attached to each other. For example, in a gear train with four gears, gear A turns clockwise, gear B turns counterclockwise, gear C turns clockwise, gear D turns counterclockwise.