a particle moving along a hoizontal line has position s$($t$),$ where s is measured in meters, t in seconds.

$($a$)$ What is the meaning of the derivative s$\text{'}($t$)?$ What are its units?

$($b$)$ What is the meaning of the derivative s$\text{'}\text{'}($t$)=($s$\text{'})\text{'}($t$)?$ What are the limits$?$