A metaphor is a figurative language device that represents one thing as if it were another, or compares two things not normally viewed as similar, such as time is a thief. This comparison draws attention to the way time is quick and stealthy. Simile
Velocity is the rate of motion, speed or action. An example of velocity is a car driving at 75 miles per hour. velocity. pl. velocity. pl. Rapidity or speed of motion; swiftness. Physics A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.
...the velocity is the 'rate of change of an object with respect to its position' it is a vector quantity, means there must specify a direction to which the object is moving. ..speed is a scalar quantity, means no need of specify the direction..these are the simplest definitions..