spike

[Benjamin Zimmer]

On 2/7/06, Mark Spahn <mspahn at localnet.com> wrote:
> The December 2003 Scientific American (page 35)
> has a citation that illustrates this meaning of "spike"
> perfectly, in the sense of both an upward-pointing spike=20
> and a downward-pointing spike.  In the description=20
> of what a sonic boom is,
>
>      A supersonic jet forms a shock wave at its nose,
>      which claps back together after its tail.  This pressure
>      suddenly spikes a couple of pounds per square foot
>      over ambient atmospheric pressure, then shoots
>      below ambient by about an equal amount, spiking
>      again before returning to ambient pressure.  A graph
>      of pressure over time would form the letter N.

See graph of N-wave here:

http://gis.esri.com/library/userconf/proc01/professional/papers/pap284/p284.htm

As I read it, the SciAm passage doesn't imply a "downward-pointing
spike". The pressure first spikes to get to ~2 psf over ambient
pressure, then drops to ~2 psf below, then spikes again to get back to
ambient pressure. So both spikes are sudden increases.

> Most dictionaries seem to ignore both the "sudden up-then-down
> (or down-then-up) movement" meaning and the "sudden increase"
> meaning of "spike".

Which dictionaries do you mean? Here's a sampling for the noun "spike":

MWCD11: an abrupt sharp increase (as in prices or rates)
Compact OED: a sharp increase in magnitude or intensity
Encarta: a sharp and brief rise in something
RHUD: an abrupt increase or rise

Senses for the verb are similar.


--Ben Zimmer

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