How is velocity defined in physics?

Velocity in physics is defined as the rate at which an object changes its position, specifically, it is the vector quantity that describes both the speed and direction of the object’s motion. This definition is encapsulated in the concept of displacement per unit time, where displacement refers to the change in position of an object from its initial point to its final point, and is a vector quantity that has both magnitude and direction.

When we consider the other definitions, while distance per unit time does measure how fast an object is moving, it is not directional and therefore describes speed rather than velocity. Speed is a scalar quantity that does not incorporate direction, making it less comprehensive than the concept of velocity.

Similarly, the idea of speed per unit distance is not a standard definition in physics—it does not convey a meaningful, conventional unit of measurement related to motion.

Lastly, acceleration per unit time expresses how quickly velocity changes over time rather than defining velocity itself. It pertains to the change in velocity, which is another distinct concept.

Overall, the choice that correctly captures the full definition of velocity is displacement per unit time, as it incorporates both the magnitude and direction of movement.