What is a derivative and how does it measure change?

Imagine you're driving up a winding mountain road. Sometimes you crawl, sometimes you zoom. A derivative is just a fancy name for one simple question: right now, this instant, how fast are things changing? Not over the whole trip — right HERE. That's the whole idea. Everything else is just clever ways to find that number.
Let's start with something you already know: speed. If you drive 60 miles in one hour, your average speed is 60 miles per hour. Easy. You took the distance and divided by the time. That's "change in position" divided by "change in time." A derivative is basically this same recipe — just zoomed way, way in.
