Where does velocity collide?

The rate at which a body's position changes with time, taken as a vector: a magnitude, which is the speed, and a direction. Galileo fixed the quantity in 1638 by showing that a body falling from rest gains equal increments of it in equal times, and Newton's second law of 1687 made its rate of change the thing a force produces. A body moving in a circle at constant speed has a changing velocity, because the direction turns, and so is accelerating. Every other meaning on this page keeps the rate and drops the direction. Only here is velocity something with an arrow on it.[1][2][3]

Unit

A body, at an instant, relative to a frame of reference

Recovery means

Not applicable, velocity is a state of motion; the question is what force is changing it

Measured by

Metres per second; displacement over a timed interval, Doppler shift, integrated accelerometer readings

The speed at which the edge of a spreading population, gene or infection advances across space. Fisher fixed it in 1937 for an advantageous gene moving through a population: local growth plus random dispersal produces a travelling wave, and the front moves at a constant speed equal to twice the square root of the growth rate times the diffusion coefficient. Skellam applied the same equation in 1951 to muskrats spreading across central Europe and showed the radius of the invaded area growing linearly in time, as the theory predicted. Velocity here belongs to a front, not to any individual: the animals wander at random, and it is the boundary of the occupied region that moves in a straight line.[4][5]

Unit

The boundary of an occupied region, over years or generations

Recovery means

Not applicable, the criterion is arrival: when the front reaches a place, and whether a barrier slows it

Measured by

Kilometres per year from the square root of invaded area, or from first-detection dates along a transect

The number of times a unit of money is spent in a period, defined as total spending divided by the money stock. Fisher fixed the equation of exchange in 1911 (money times velocity equals prices times transactions) and treated velocity as a slow-moving fact about payment habits, so that a change in money moved prices. Friedman's 1956 restatement turned velocity into the outcome of a demand for money that depends on interest rates, wealth and expected inflation, and the quantity theory into a claim that this demand is stable. Bordo and Jonung showed in 1981 that velocity in five countries fell for decades as banking spread and then rose as substitutes for money appeared, which is to say it is an institution, not a constant. Nothing is moving through space. Velocity is a ratio of two flows.[6][7][8]

Unit

An economy, over a quarter or a year

Recovery means

Not applicable, the criterion is stability: whether velocity is predictable enough for money to forecast spending

Measured by

Nominal GDP divided by a money aggregate such as M1 or M2; turnover of deposits

In retail, the rate at which a product sells through a store (units per store per week) used to decide whether a new line keeps its shelf space. Sandoh and Larke built a 2002 model for exactly that decision in Japanese convenience stores, where a product's sales velocity in a trial period decides whether it is delisted. In business-to-business selling the same word names the speed at which opportunities move through the pipeline, and the practitioner formula multiplies the number of opportunities, their value and the win rate and divides by the length of the sales cycle. Paschen, Wilson and Ferreira's 2020 review of AI along the sales funnel treats the stages and their conversion rates as the object to be accelerated. Velocity here is a throughput, and the thing moving is revenue.[9][10]

Unit

A product in a store, or an opportunity in a pipeline, over a selling period

Recovery means

Not applicable, the criterion is a threshold: enough velocity to stay listed, or enough to make the quarter

Measured by

Units per store per week; pipeline value times win rate divided by cycle length

The rate at which data is generated and must be ingested and acted on, one of the three dimensions, with volume and variety, that Laney used in a 2001 META Group research note to describe the strain on data management. Gandomi and Haider's 2015 review fixed the current usage: velocity is the speed of data creation and the corresponding demand for real-time analysis, and the three Vs are a description of the data, not of anything done with it. A sensor stream and a clickstream have velocity; a data warehouse loaded nightly does not. Velocity here is a property of an input, and the response to it is architecture: stream processing instead of batch.[11]

Unit

A data source or pipeline, in events per second

Recovery means

Not applicable, the criterion is latency: whether analysis keeps pace with arrival

Measured by

Events or bytes per second at ingestion; end-to-end latency from event to decision

The amount of work a Scrum team finishes in one sprint, counted in story points or another relative unit, and used to forecast how much of the backlog the team can take on next. Cohn fixed the practitioner definition in 2005: estimate every story in points, sum the points for stories completed in a sprint, and plan the next sprint from the running average. The Scrum Guide itself never uses the word, and the 2020 edition leaves the measure to the team. Hearty, Fenton, Marquez and Neil built a Bayesian model in 2009 that predicts velocity from a project's history and warns that it drifts. Velocity here is a team's own yardstick, in a unit the team invented, and comparing two teams' numbers is meaningless by construction.[12][13][14]

Unit

One team, over one sprint, in that team's points

Recovery means

Not applicable, the criterion is predictability: whether the next sprint's velocity matches the average

Measured by

Sum of story points for stories accepted as done in the sprint; rolling average over recent sprints