  Almost all theories of physics have expressed physical laws by means of
differential equations. One can ask: why differential equations? What is
special about them? This article addresses these questions and is presented as
an inquiry-based lecture, where students and a teacher are engaged in
discussion. It has two goals: (1) To help undergraduate students understand the
rationale behind the use of differential equations in physics, (2) To show how
meaningful and interactive presentation of mathematics can help students take
pleasure in learning physics.
