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Why do reporters (and sometimes police officers) say that somebody was going at a high rate of speed when they actually mean high speed?

In physics, speed is already the rate of distance over time, otherwise known as velocity. Rate of speed is velocity over time, otherwise known as acceleration. By saying high rate of speed they would be implying picking up more speed.

Is there a social reason for using high rate of speed rather than high speed?

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  • The way I read it, "accelerating momentum" could just as easily refer to increasing the mass while keeping the velocity constant.
    – mmyers
    Commented Aug 26, 2010 at 17:47
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    Good question. I agree with your analysis and cannot find any reason why anyone would say "high rate of speed" other than pure ignorance.
    – Lightness Races in Orbit
    Commented Jan 18, 2011 at 5:20
  • @mmyers: How? If you're increasing the mass while keeping the velocity constant, you're just increasing the momentum, not accelerating it.
    – ShreevatsaR
    Commented Jan 25, 2011 at 14:41

5 Answers 5

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Because more words = more official-sounding. It's a bad phrase that has taken root in irrelevant situations. Adding "rate" adds nothing in most contexts.

However, the word rate also means "value" or "number". From Cambridge:

rate (MEASUREMENT)

noun

a measurement of the speed at which something happens or changes, or the number of times it happens or changes, within a particular period

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    Now it's 3 times worse using the first definition: "high 'measurement of the speed' of speed". Or just as bad original using the second definition: "high 'number of times' [the] speed 'changes within a particular period'".
    – Ants
    Commented Aug 26, 2010 at 18:07
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    @Ants: Thank you. From the literal bottom of my decimated heart. :)
    – Goodbye Stack Exchange
    Commented Aug 26, 2010 at 18:24
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    "the number of times it happens or changes, within a particular period" is more or less the 'speed', so "high rate of speed" still means "high speed of speed", whatever definition you pick.
    – ShreevatsaR
    Commented Jan 25, 2011 at 14:34
  • @GoodbyeStackExchange the word rate also means "value" or "number". No. The definition you quoted does not say that. It says the speed at which something happens or changes. "Rate of speed" means "acceleration", which is how fast your speed is changing. "Speed" has units of distance per time (eg miles per hour). "Rate of speed" has units of distance per time per time. As an example, if your speed was increasing by 5 mph every second, your rate of speed would be 5 miles per hour per second, so a speed (5 mph) per a time (1 second). "Rate of speed" as used should be just "speed".
    – Bohemian
    Commented Jan 31, 2022 at 22:29
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The very first sense for the noun rate in Merriam-Webster is “reckoned value : valuation”. The word has more meanings than the one used in physics. One could therefore make the argument that a rate of speed is a speed which is reckoned (i.e. by measuring or reasoned estimation) rather than guessed.

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  • That's the first sense, but surprisingly to me none of the example sentences seem to reflect that sense (rather than, say, 4a).
    – ShreevatsaR
    Commented Jan 25, 2011 at 14:40
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In the Ontario Highway Traffic Act, S 128, the term "Rate of Speed" is used throughout. I suspect this term did not originate in Ontario, but the usage has become official due to its inclusion in legislation.

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  • I think you could make a case for getting off a speeding ticket if the law uses “high rate of speed” if the officer can’t report what your acceleration was, which is what your rate (ie change) of speed is. You would need a physics professor to testify. It could be fun.
    – Bohemian
    Commented Jan 29, 2021 at 7:41
  • @Bohemian I think they mean the given rate of speed, not the rate of change of speed with respect to time.
    – mchid
    Commented Jan 31, 2022 at 18:37
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    @mchid "rate" means difference/change per time. Speed is the distance change per time, that's why speed has units mile per hour - a distance per a time. So the rate of speed is the change in speed per time, which we call acceleration and has units of distance change per time per time, for example "miles per hour per second". So, "rate of speed" and "rate of change of speed with respect to time" mean exactly the same thing - one is just the long winded version of the other. Only North Americans say "rate of speed" when they really mean "speed". The rest of world just says "speed".
    – Bohemian
    Commented Jan 31, 2022 at 22:19
  • @Bohemian Yes, I understand this. Speed is the scalar unit or the magnitude of velocity but they are referring to the given rate at which speed is of (distance/time) and not the rate of speed itself. Also, if you write it out: the rate of the change of speed with respect to time, you get Δs/t. However, if we simply write the "rate of speed", not the rate of change Δ of speed (s) and not with respect to time (t), then the rate of speed is simply s isn't it?
    – mchid
    Commented Feb 1, 2022 at 16:18
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As a scientist, I would point out that saying "high rate of speed", when one simply means "high speed", is not merely redundant but outright wrong. Speed is already a rate in itself (the rate at which distance changes).

According to my dictionary*, the relevant definition of rate is

the speed with which something moves, happens or changes

*New Oxford American Dicitionary (2nd Edition)

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    Well actually IMO, "rate of speed" doesn't mean acceleration; it's just meaningless. It makes sense to talk of "rate" for processes (like "rate of growth"), but if you want to talk of acceleration, you must say "rate of change of speed" rather than "rate of speed" (which means "speed of speed", which is meaningless).
    – ShreevatsaR
    Commented Jan 25, 2011 at 14:37
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    @ShreevatsaR: True, now that I think of it.
    – Jimi Oke
    Commented Jan 26, 2011 at 1:38
  • Isn't it understood to be the given rate of speed: the rate that is speed?
    – mchid
    Commented Jan 31, 2022 at 18:41
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This is classic genteelism.

Speed is the rate of change of position.

Although "Rate of speed" is technically meaningless, it does, however, usually convey the intended meaning (for better or worse).

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    “Rate of speed” is not meaningless. In fact, it has a precise and unambiguous definition: acceleration. Acceleration is defined as the rate of change of speed, which is in turn defined as the rate of change of location.
    – Bohemian
    Commented Jan 29, 2021 at 7:38
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    Ok, but you've defined acceleration twice: "rate of speed" and "rate of change of speed". Those are two different things. (Actually I still think "rate of speed" is not really a thing or at best it is redundantly describing "speed".)
    – shaunmartin
    Commented Nov 27, 2023 at 20:49
  • No, I haven't define it twice. "Rate" means "change per time". "Rate of something" is shorthand for "Rate of change of something (with respect to time)". They are the same thing. Speed is the rate of change of position. Acceleration is the rate of change of speed.
    – Bohemian
    Commented Nov 28, 2023 at 0:17

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