Calculus. Surely any child who has ever ran, or ever seen a hill, knows about velocity and slopes - concrete instances of the abstract concept. But I would say

Calculus. Surely any child who has ever ran, or ever seen a hill, knows about velocity and slopes - concrete instances of the abstract concept. But I would say that that's not math, any more than speaking means you know grammar, or digesting means you know biochemistry. Math is formalization. For calculus, it's slopes at a point without dividing by zero (using the cheat of limits).