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?

  • The way I read it, "accelerating momentum" could just as easily refer to increasing the mass while keeping the velocity constant. – mmyers Aug 26 '10 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 with Monica Jan 18 '11 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 Jan 25 '11 at 14:41

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:



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 Aug 26 '10 at 18:07
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    @Ants: Thank you. From the literal bottom of my decimated heart. :) – Neil Fein Aug 26 '10 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 Jan 25 '11 at 14:34

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.

  • That's the first sense, but surprisingly to me none of the example sentences seem to reflect that sense (rather than, say, 4a). – ShreevatsaR Jan 25 '11 at 14:40

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).


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 Jan 25 '11 at 14:37
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    @ShreevatsaR: True, now that I think of it. – Jimi Oke Jan 26 '11 at 1:38

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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