This is a unit of frequency. Frequency is the number of times that an event occurs in a given length of time. For example, a hummingbird’s heart can beat (a periodic action) as fast as 1,260 times per minute. That’s a frequency. Scientists can measure that frequency in hertz. One hertz is equal to one cycle per second. If hummingbird’s heart beats at 1,260 beats per minute, that’s 21 beats per second, a frequency of 21 hertz.
Many things can be measured in hertz, from waves beating on a beach to the frequency of sounds. Our range of hearing extends from about 20 hertz (which we hear as a very low pitch) to 20,000 hertz (a very high pitch). So a hummingbird’s heart might sound like a very low hum.
The unit hertz is named for Heinrich Rudolf Hertz, a German physicist who lived from 1857 to 1894. He proved the existence of electromagnetic waves — waves of energy including visible light, radio waves, microwaves and more. All of those waves can now be measured in hertz.
In a sentence
Playing sound frequencies around 25,000 hertz might annoy deer enough to keep them away from dangerous roads.