Hertz

Hertz (Hz) is a unit of frequency, measured in s^-1, or one over seconds. It is used to measure how many times something happens in a second. Hertz are an important unit for defining waves, where frequency is one of the defining characteristics.

A more specific unit, related to the Hz, is the RPM (rotations per minute). Two useful conversions: 1 RPM = 0.0167 Hz and 60 RPM = 1 Hz

Electrical grid

The electrical grid in North America and Japan runs at 60 Hz, while the European grid runs at 50 Hz. This means that the voltage on the electrical grid hits its maximum value 60 (or 50) times in a second.