thin wheel with teeth that engage with a chain | a wheeled vehicle that has two wheels and is moved by foot pedals |
tooth on the rim of gear wheel | a single complete execution of a periodically repeated phenomenon |
roller that has teeth on the rims to pull film or paper through | a periodically repeated sequence of events |
| a series of poems or songs on the same theme |
| an interval during which a recurring sequence of events occurs |
| the unit of frequency; one hertz has a periodic interval of one second (named for Heinrich Rudolph Hertz) |