Related rates are changes that relate to each other, usually with respect to time. If a [[Function|function]] $F$ is defined such that $F = f(x)$, then the derivative of $F$ can be taken with respect to another variable. If $x$ is a function of $t$ ($x = g(t)$), Then $F = f(g(t))$, applying the [[Math/Calculus/Derivative/Chain Rule|chain rule]]: $ \frac{dF}{dt} = \frac{df}{dx} \cdot \frac{dx}{dt} $