The unit of acceleration in the FPS (Foot-Pound-Second) system is feet per second squared (ft/s²).

Here's why:

* Acceleration is the rate of change of velocity over time.

* Velocity is the rate of change of displacement over time, measured in feet per second (ft/s) in the FPS system.

* Therefore, acceleration is the change in velocity (ft/s) divided by the change in time (s), resulting in feet per second squared (ft/s²).