Final answer:
The lower limit of acceleration that people can perceive is approximately 0.128g, much lower than the extreme accelerations experienced in military or spaceflight scenarios like jet fighter ejections, where accelerations can reach 45 g's.
Step-by-step explanation:
The lower limit of acceleration perceptible to people is set by observation and experiment at approximately 0.128g. This value represents the threshold at which human beings can generally start to sense acceleration. It is significantly smaller than the extreme accelerations experienced by fighter pilots or astronauts, which can be many times greater than Earth's gravitational acceleration (9.80 m/s²). For example, during emergency jet fighter ejections, accelerations can reach as high as 45 g's, equivalent to 45 × 9.80 m/s² or approximately 440 m/s². This is a much higher acceleration than we can comfortably perceive or withstand long term. It's crucial to understand such accelerations to protect humans during high-speed travel such as in military applications and spaceflight.