What is defined as the change in velocity per unit of time?

Acceleration is defined as the change in velocity per unit of time. It measures how quickly an object is increasing or decreasing its speed or changing its direction. In physics, acceleration is an important concept, as it helps to quantify the motion of objects under the influence of forces. For instance, a car speeding up from a stop or a ball being thrown upward experiences acceleration.

The other concepts presented relate to different areas of physics. The theory of relativity is focused on the relationship between space and time rather than directly addressing the concept of velocity change. Newtonian motion refers to classical mechanics and the laws of motion developed by Sir Isaac Newton that govern the motion of objects but are not themselves a direct measurement of change in velocity. Aerodynamics is the study of the behavior of air as it interacts with solid objects, particularly the forces involved in the motion of objects through the air, but it does not define acceleration.