The rate at which velocity changes is called acceleration.
Acceleration measures how quickly an object changes its velocity. It can indicate an increase in speed, a decrease (which is actually called deceleration), or a change in direction. In physics, acceleration is typically calculated as the change in velocity divided by the time during which the change occurs. This relationship is often expressed in the formula:
a = Δv / Δt
where a is acceleration, Δv is the change in velocity, and Δt is the change in time. Thus, understanding acceleration is crucial in the study of motion and helps us to describe how fast an object is speeding up or slowing down.