“Momentum may be roughly described as quantity motion. A body moving at a speed of say twenty an hour, has a certain quantity of motion. If the body goes forty miles an hour there is twice as motion; or if twice as much matter goes twenty miles hour, there is also twice as much motion. Momentum is measured by the quantity of matter moving at a rate mass \times velocity.”

—  William Kingdon Clifford

"Energy and Force" (Mar 28, 1873)

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William Kingdon Clifford 48
English mathematician and philosopher 1845–1879

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