Final answer:
The SI units of acceleration are m/s², representing the rate of change of velocity per second and can be due to changes in speed or direction.
Step-by-step explanation:
The units of acceleration are m/s², which stands for meters per second squared or meters per second per second. This unit represents how many meters per second the velocity of an object changes every second. Acceleration, being a vector, has both a magnitude and direction, and it can occur due to changes in the speed or direction of the velocity. A familiar example of acceleration due to gravity is 9.8 m/s² on Earth's surface.