# Hertz facts for kids

Kids Encyclopedia Facts
A sine wave with varying frequency

The hertz (symbol: Hz, definition: 1/s) is a unit derived from time which measures frequency in the International System of Units (SI). Frequency is how often something happens. A frequency of 1 hertz means that something happens once a second. The note Middle C (the C in the middle of the piano) is 261.65 (262) Hz. This means there are 262 vibrations every second, which is heard as the note Middle C, when that piano key is played.

Humans are able to hear sounds between 20-20 000 Hz. Owls are able to hear sounds between 200–12000 Hz.

The basic unit is 1/second. The unit is named after a German physicist Heinrich Rudolf Hertz.

## Multiple units

1000 hertz is 1 kilohertz. 1000 kilohertz is 1 megahertz, 1000 megahertz is 1 gigahertz: (see table)

Unit Equal to:
Kilohertz (KHz) 1000 Hz
Megahertz (MHz) 1000 kHz
Gigahertz (GHz) 1000 MHz
Terahertz (THz) 1000 GHz
Petahertz (PHz) 1000 THz
Exahertz (EHz) 1000 PHz
Zettahertz (ZHz) 1000 EHz
Yottahertz (YHz) 1000 ZHz

## Examples

• The frequency of the Earth's spinning (once per ~24 hours) is about 12 microhertz (much smaller than 1 Hz).
• The hertz is sometimes used to measure the power of a processor in computing and electronics.
• Amateur radio in the United States Of America is at different frequencies between 1.8 and 1300 MHz
• Air traffic control uses frequencies between 3 and 25 MHz as well as frequencies between 108 and 136 MHz
• Musical note middle G (G4) has a frequency of 392 Hz.

## See also

In Spanish: Hercio para niños

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Hertz Facts for Kids. Kiddle Encyclopedia.