Which concept describes the rate of change of an object's velocity?

The concept that describes the rate of change of an object's velocity is acceleration. Acceleration is defined as the change in velocity over a specific period of time. This means that if an object is speeding up, slowing down, or changing direction, it is experiencing acceleration. In mathematical terms, acceleration is calculated as the difference in velocity divided by the time taken for that change to occur.

For instance, when a car speeds up from a stop, the increase in its velocity over the time taken to reach a certain speed is its acceleration. Similarly, if the car applies brakes and reduces its speed, that decrease in velocity also represents acceleration in the negative direction.

In contrast, magnitude refers to the size or extent of a quantity without regard to its direction, inertia refers to an object's resistance to changes in its state of motion, and velocity is a vector quantity that indicates the speed of an object in a given direction. These concepts support understanding motion but do not define the rate at which velocity changes, which is explicitly the definition of acceleration.