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Frequency

From Tilcayo Cats, the lean encyclopaedia by Tilcayo Knowledge Systems
This article is about frequency in physics. For the use of the word in statistics, see § In statistics.

Frequency is the number of times an event happens in a given unit of time. For something that repeats regularly, the frequency is the number of back-and-forth movements (oscillations) in each unit of time.[1] The International System of Units measures frequency in hertz (Hz); one hertz is one cycle per second.[2]

Frequency and period

The time it takes for one complete oscillation, or cycle, is called the period, written T.[3][4] Frequency and period are closely linked: the frequency f is one divided by the period, f = 1/T.[5] An everyday example shows the idea: if someone is paid twice a month, the frequency of payment is two per month and the period between payments is half a month.[6]

Unit

One hertz means one cycle each second.[2] The hertz is also tied to how the second itself is defined. The Bureau International des Poids et Mesures defines the second, the SI unit of time, by fixing the frequency of a particular change in the caesium-133 atom at exactly 9,192,631,770 Hz.[7]

Waves and sound

For all waves, including sound, the speed of the wave equals its frequency multiplied by its wavelength, written v = fλ.[8] The wavelength is the distance between neighbouring matching parts of a wave, such as two crests.[9] In music, shorter strings vibrate faster, so they make sounds of higher pitch.[10]

In statistics

In statistics, frequency means the number of times a particular answer or value occurs in a set of data. The relative frequency is that number divided by the total number of values in the sample.[11]

See also

References

  1. ↑ Ling, Samuel J.; Sanny, Jeff; Moebs, William (2016). "15.1 Simple Harmonic Motion". University Physics Volume 1. OpenStax, Rice University. Retrieved 18 October 2026. Frequency ( f ) is defined to be the number of events per unit time. For periodic motion, frequency is the number of oscillations per unit time.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ↑ 2.0 2.1 Ling, Samuel J.; Sanny, Jeff; Moebs, William (2016). "15.1 Simple Harmonic Motion". University Physics Volume 1. OpenStax, Rice University. Retrieved 18 October 2026. The SI unit for frequency is the hertz (Hz) and is defined as one cycle per second{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. ↑ Ling, Samuel J.; Sanny, Jeff; Moebs, William (2016). "15.1 Simple Harmonic Motion". University Physics Volume 1. OpenStax, Rice University. Retrieved 18 October 2026. In the absence of friction, the time to complete one oscillation remains constant and is called the period ( T ) .{{cite book}}: CS1 maint: multiple names: authors list (link)
  4. ↑ Ling, Samuel J.; Sanny, Jeff; Moebs, William (2016). "15.1 Simple Harmonic Motion". University Physics Volume 1. OpenStax, Rice University. Retrieved 18 October 2026. A cycle is one complete oscillation .{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ↑ Ling, Samuel J.; Sanny, Jeff; Moebs, William (2016). "15.1 Simple Harmonic Motion". University Physics Volume 1. OpenStax, Rice University. Retrieved 18 October 2026. The relationship between frequency and period is f = 1 T .{{cite book}}: CS1 maint: multiple names: authors list (link)
  6. ↑ Urone, Paul Peter; Hinrichs, Roger (2022). "16.2 Period and Frequency in Oscillations". College Physics 2e. OpenStax, Rice University. Retrieved 18 October 2026. For example, if you get a paycheck twice a month, the frequency of payment is two per month and the period between checks is half a month.{{cite book}}: CS1 maint: multiple names: authors list (link)
  7. ↑ "SI base unit: second (s)". Bureau International des Poids et Mesures. Retrieved 18 October 2026. The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency Δν Cs , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s –1 .
  8. ↑ OpenStax (2020). "14.1 Speed of Sound, Frequency, and Wavelength". Physics. OpenStax, Rice University. Retrieved 18 October 2026. The relationship between the speed of sound, its frequency, and wavelength is the same as for all waves: v = f λ
  9. ↑ OpenStax (2020). "14.1 Speed of Sound, Frequency, and Wavelength". Physics. OpenStax, Rice University. Retrieved 18 October 2026. Recall that wavelength is defined as the distance between adjacent identical parts of a wave.
  10. ↑ OpenStax (2020). "14.1 Speed of Sound, Frequency, and Wavelength". Physics. OpenStax, Rice University. Retrieved 18 October 2026. In musical instruments, shorter strings vibrate faster and hence produce sounds at higher pitches.
  11. ↑ Illowsky, Barbara; Dean, Susan (2023). "2.2 Histograms, Frequency Polygons, and Time Series Graphs". Introductory Statistics 2e. OpenStax, Rice University. Retrieved 18 October 2026. The relative frequency is equal to the frequency for an observed value of the data divided by the total number of data values in the sample. (Remember, frequency is defined as the number of times an answer occurs.){{cite book}}: CS1 maint: multiple names: authors list (link)
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