Which of the following describes velocity?

Velocity is defined in physics as a vector quantity that describes both the speed of an object and the direction in which it is moving. This means that to fully understand velocity, you must consider not just how fast an object is traveling (which is its speed), but also the path or direction it is taking. For instance, if a car is moving at 60 miles per hour to the north, this specific description incorporates both the speed and direction, making it a complete representation of the object's motion.

The other choices focus on related concepts but do not fully capture the definition of velocity. For example, the change of position over time refers to the basic idea of motion, while total distance traveled only accounts for how far an object has moved without considering direction. Speed without direction describes the magnitude of motion but lacks the directional component that is essential to the definition of velocity. Thus, the most accurate description of velocity is that it is a variable that specifies both speed and direction.