The time rate of change of position of a body without regard to direction. It is the numerical magnitude of a velocity and hence is a scalar quantity. Linear speed is commonly measured in such units as meters per second, miles per hour, or feet per second. It is the most frequently mentioned attribute of motion.
Average linear speed is the ratio of the length of the path Δs traversed by a body to the elapsed time Δt during which the body moved through that path, as in Eq. (1),
Instantaneous speed, defined by Eq. (2),