form of symbology to represent such hypothetical scenarios: we replace
the Greek letter “delta” (, meaning “change”) with the roman letter “d” (meaning differential ).
A simple way of picturing the meaning of “d” is to think of it as meaning an infinitesimal interval of
whatever variable follows the “d” in the equation72. When we set up two differentials in a quotient,
we call the d
d fraction a derivative. Re-writing our average flow rate equations in derivative (calculus)
form