How is acceleration best defined?

Acceleration is best defined as a body's rate of change of velocity. This definition captures the fundamental concept of acceleration, which is the measure of how quickly an object is speeding up or slowing down. It is a vector quantity, meaning it has both magnitude and direction, and it reflects how an object's velocity (which combines both speed and direction) changes over time.

Mathematically, acceleration is often expressed in units like meters per second squared (m/s²), which indicates how much the velocity of an object increases or decreases per second. Understanding acceleration is crucial in various fields, including physics and engineering, as it helps in analyzing motion, predicting the behavior of moving objects, and ensuring safety in systems involving movement.

In contrast, other definitions do not accurately capture the essence of acceleration. The increase of displacement refers to distance traveled rather than how fast that distance is changing in terms of speed. Expressing units as km/h refers specifically to speed, which measures how fast an object is moving but does not account for changes in that speed. Lastly, defining acceleration as the rate of change of time is not accurate since time itself is not changing to cause acceleration; rather, acceleration is concerned with how velocity changes over a given time interval.