In the summer of 1666, Isaac Newton saw an apple fall in his garden, and promptly invented the theory of gravity. That, at least, is the story.
And, however oversimplified this version of events may be, it makes as good a starting point as any for an introduction to calculus.
Because the apple speeds up as it falls.
It even raises the whole question of what we mean, exactly, by the speed of the apple at any given moment.