Rapidity
In relativity, rapidity is an alternative to speed as a measure of motion. On parallel velocities (say, in one-dimensional space) rapidities are simply additive, unlike speeds at relativistic velocities. For low speeds, rapidity and speed are proportional, but for high speeds, rapidity takes a larger value. The rapidity of light is infinite. The rapidity concept is not widely (nor fashionably) used; speed has the advantage of more direct measurability.
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Famous quotes containing the word rapidity:
“Life is measured by the rapidity of change, the succession of influences that modify the being.”
—George Eliot [Mary Ann (or Marian)
“They look quite promising in the shop; and not entirely without hope when I get them back into my wardrobe. But then, when I put them on they tend to deteriorate with a very strange rapidity and one feels so sorry for them.”
—Joyce Grenfell (1910–1979)
“No one is ahead of his time, it is only that the particular variety of creating his time is the one that his contemporaries who are also creating their own time refuse to accept.... For a very long time everybody refuses and then almost without a pause almost everybody accepts. In the history of the refused in the arts and literature the rapidity of the change is always startling.”
—Gertrude Stein (1874–1946)