Final answer:
The number of times an event occurs within a unit of time is termed 'frequency', and the rate of change of velocity per unit time is called 'acceleration', measured in meters per second squared.
Step-by-step explanation:
The term that describes the number of times an event occurs within a unit of time is known as frequency. In physics, this concept is often applied to periodic events, such as oscillations or cycles. For example, the frequency of a pendulum's swing would be the number of swings it completes per second. When we apply this concept to motion, the rate of change of velocity per unit time is called acceleration, which is measured in meters per second squared (m/s²) in the International System of Units (SI). Acceleration is an important concept in Newtonian mechanics and is central to understanding motion.
Example of Rate per Unit Time
If a car's velocity increases from 0 m/s to 20 m/s in 4 seconds, the average acceleration would be calculated by dividing the velocity change (20 m/s) by the time (4 s), resulting in an acceleration of 5 m/s².