momentum
- 1The impetus of a body in motion, or of an idea or course of events.
The reform effort lost momentum once its main sponsor left office.
The cyclist used the momentum from the descent to climb the next hill.
Note
Here motion is carried over to people, plans and stories. In Thomas Hardy's Two on a Tower (1882), an intention to marry, timid at first, "accumulated momentum with the lapse of hours." In Hawthorne's Mosses from an Old Manse (1843), travelers are full of momentum caught from the cars. In older use it could even mean a moment, its Latin twin.
- 2The force or strength that something builds up as it moves.
The runners picked up momentum on the gentle slope before the final stretch.
A spinning flywheel stores momentum that can be released to drive the machine.
Note
Less a quantity than a build-up: the force something acquires by moving, and the reason a rolling or falling object grows harder to stop. Where the mass-times-velocity quantity is calculated, this sense is described. It takes verbs of accumulation: a body gains or picks up momentum rather than having a value of it.
- 3The tendency of a moving body to keep moving, equal to the product of its mass and its velocity.
The momentum of a moving particle equals its mass times its velocity.
Engineers calculate the momentum of each component to predict how the parts will behave after impact.
Note
Physics gives the word its exact form: mass multiplied by velocity. Because velocity has a direction, so does momentum. The momentum of a system of bodies is therefore found by adding the individual products as vectors, not as plain numbers. The word is Latin mōmentum, a doublet of moment and movement, and it has two plurals, momenta and momentums.
- 4In market analysis, the presumed tendency of an asset's existing price trend to keep accelerating in its current direction.
Analysts noted that the rally had lost momentum as trading volume thinned.
The strategy buys assets showing strong momentum and sells those whose trend is fading.
Note
Traders borrowed the physicist's word for a bet rather than a law. In technical analysis, momentum is a surmise: the reading that a price already moving fast will keep accelerating the same way. Unlike the physics quantity, nothing guarantees it persists. That is why analysts speak of a rally losing momentum, and treat it as a signal to weigh, not a measurement.
Practice
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Origin
From Latin "mōmentum", making it a doublet of "moment" and "movement".