Talk:Hertz

Megahertz and Kilohertz pages

Can the pages Megahertz, Kilohertz etc be more than stubs?

Should we redirect them here, where we can put a list of SI multiples? -- — Preceding unsigned comment added by Tarquin (talk • contribs) 12:26, 28 December 2002 (UTC)

No. I think we should also have picohertz, yottahertz etc. Just kidding. It might be useful think about consolidating all these SI pages so that the article is at the preferred SI standard with all the other prefixed stuff redirecting to it. Hm. That would mean that gram would redirect to kilogram, kilometre to metre, square kilometre to square metre etc. --— Preceding unsigned comment added by Mav (talk • contribs) 12:44, 28 December 2002 (UTC)

One picohertz is approximately equivalent to once per 31710 years. — JIP | Talk 15:11, 1 May 2005 (UTC)

For some strange reason the above comment had been deleted over fifteen years ago, with no real explanation. JIP | Talk 20:20, 12 December 2021 (UTC)

Megahertz should be left as-is, whereas the rest (e.g. Kilohertz) should simply be merged into Hertz.— Preceding unsigned comment added by 195.92.168.179 (talk) 17:45, 4 March 2004 (UTC)

maybe there should be a page like Orders of magnitude (power). Yonir 00:46, 27 August 2005 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Hertz/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

The rad/s to Hz conversion shown is confusing. It would be clearer to write: 1 rad/s = 2π Hz, or 1 Hz = (1/2π) rad/s, where as usual the units follow the numerical measures. (I tried to edit the article, but my command of the syntax wasn't good enough.) Spock2 19:46, 25 July 2007 (UTC)

Last edited at 19:46, 25 July 2007 (UTC). Substituted at 17:51, 29 April 2016 (UTC)

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Amazingly well written intro to this article.

Should be a featured article. — Preceding unsigned comment added by Rhodechill (talk • contribs) 04:14, 28 April 2017 (UTC)

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Blinking lights Image shows wrong frequency

The bottom light should blink with 2 Hz, but one full on-off cycle takes 1 second, so it is actually 1 Hz. The definition of Hertz is for full cycles, not half cycles, so while it is true that the light is on for 0.5 seconds, that doesn't make the frequency 2 Hz. 130.75.213.44 (talk) 10:53, 24 February 2021 (UTC)

Agreed. I have removed the image for now. Danstronger (talk) 23:00, 12 December 2021 (UTC)

This week the gif creator again added a gif that has wrong speeds. So I replaced it with the old image that was used until July 2020. It is used on numerous pages. 63.226.236.153 (talk) 09:19, 24 February 2022 (UTC)

Cycle is not a unit

Boppennoppy is correct. The authoritative source here is the SI Brochure, which defines the hertz (Hz) as 1 s^-1. The cycle is not a unit. Dondervogel 2 (talk) 15:58, 30 December 2021 (UTC)

"one per second" is a very awkward phrase that is not implied by "1 s^-1" and that makes the reader ask "one what?" "Cycle" is appropriate because Hertz is a unit of frequency and cycle is a generic term for whatever is repeating that has a frequency. "Cycle per second" is also the standard dictionary definition. "1 s^-1" is not a definition but an SI equivalent, as shown in the infobox. Danstronger (talk) 17:12, 30 December 2021 (UTC)

Four points:

• It would be correct to say that the numerical value of frequency, when expressed in hertz, is equal to the number of cycles per second, but that statement does not make the cycle a unit. Standardization bodies like BIPM and NIST do not mention the "cycle" and instead state that 1 Hz is equal 1 s^-1. In a sloppy kind of way it's OK to say they are the same, but sloppiness is not what I seek in an encyclopaedia. We should be precise.
• It hasn’t always been that way. There was a time when “cycle per second” (cps) was considered a unit, complete with kilocycle per second (kcps), megacycle per second (Mcps) and so on. But such units are obsolete and the article should make that clear.
• "One per second" is precisely what is meant by 1 s^-1 (in the same way that "one metre" is meant by 1 m). What else would it mean?
• It’s clear to me that Boppennoppy is trying to improve the article, making changes that are substantiated by reference to international standards. I understand your point of view as well (though I do not agree with it), but just because you are in a majority does not make you right. I suggest we seek a form of words that acknowledges both the precise definition (citing BIPM and NIST), and the sloppy one (citing whichever sources you consider appropriate).

Dondervogel 2 (talk) 17:54, 30 December 2021 (UTC)

I know it's not exactly what you wanted but I added a sentence about hertz being an SI derived unit (which I agree is important) to the lead. I think it's important to distinguish between a definition, which is explanatory English, and an "expression in terms of SI base units" which is the column heading in the NIST reference. Both have their virtues, but "cycle" is part of the definition, even if it's "not a unit", and I think it's correct for the article to start with a definition. Danstronger (talk) 18:52, 30 December 2021 (UTC)

Many people, when they read "one per second", have a natural tendency to ask (themselves), "one what per second?" And the associated tendency is to insert some general term for a periodic event such as "cycle". But consider a digital readout on a clock showing the number of seconds passing since some starting time. The number on the display is increasing at a rate of ONE per second—which makes perfectly good sense. Since (temporal) frequency is the quotient of the number of periodic events and the corresponding elapsed time, the dimension is number/time, 1/T, where "1" is the symbol for the dimension number, to be shown in the same special font (e.g. Helvetica) as that used for other dimension symbols. [It is not the numeral 1.] The SI (implicit) "unit" for (the quantity) number is one, 1. For time, it is second, s. So the SI unit for frequency is 1/s or "one per second", also written as s^–1.

By the way, the same "problem" occurs with quantities like number density: number per volume. Some people will ask (themselves) "number of what per volume?" And will have an urge to insert some "downstream-from-the-SI" symbol such as mcl (molecule), pcl (particle), or some other descriptive symbol—analogous to inserting cyl (cycle) in the case of frequency. If we are dealing with number density, the correct unit is 1/m³, "one per cubic metre", or m^–3. On the other hand, if we are dealing with amount density, the appropriate unit is "entities per cubic metre", ent/m³ or ent m^–3, where "ent" stands for one entity—which should be recognised as the appropriate atomic-scale unit for amount, paralleling the dalton for mass. One mole is exactly 6.02214076 x 10²³ ent. The Avogadro constant (not number) is exactly 1/ent, one per entity.

[I have been trying to get ent recognised as the appropriate atomic-scale unit for amount for over a decade. The atomic-scale unit for amount-specific ("molar") mass is then Da/ent, which, for all practical purposes, is identical to g/mol and kg/kmol. But that is another long story.] Boppennoppy (talk) 16:33, 10 November 2024 (UTC)

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Relationship between angular velocity and rotational frequency

The relationship between angular velocity, ω, with unit rad/s, and rotational frequency, f, with unit Hz (1/s), is universally given as:

ω = 2π f

which is dimensionally incorrect, with a mismatch of units: rad/s on the LHS and 1/s on the RHS. The rotational frequency is the time rate of change of the number of revolutions, N_rev = θ/rev, where θ is the angular displacement and rev is an angle of one revolution. Thus:

f = dN_rev/dt = d(θ/rev)/dt = (dθ/dt)/rev = ω/rev = ω/(2π rad)

So the dimensionally correct (and consistent-unit) relationship is:

ω = rev f = (2π rad) f

Note that, for numerical values in consistent units:

[ω/(rad/s)] = (2π rad) f /(rad/s) = 2π f /(1/s) = 2π [f /Hz]

In other words, it is the numerical values of ω and f (when expressed in rad/s and Hz, respectively) that are related by the ubiquitous formula, not the physical quantities themselves.

PS The well-known formula is "correct" in SI units, where the so-called "angular velocity" is the physical angular velocity divided by one radian—in other words, the time rate of change of the number of radians, with unit 1/s (but not Hz).

Boppennoppy (talk) 18:59, 10 November 2024 (UTC)