I feel that matter has properties which physics tells you. - George Gamow

It was a bank holiday, and Mr Tompkins, the little clerk of a big city bank, slept late and had a leisurely breakfast. Trying to plan his day, he first thought about going to some afternoon movie and, opening the morning paper, turned to the entertainment page. But none of the films looked attractive to him. He detested all this Hollywood stuff, with infinite romances between popular stars. If only there were at least one film with some real adventure, something unusual and maybe even fantastic about it. But there was none. Unexpectedly, his eye fell on a little notice in the corner of the page. The local university was announcing a series of lectures on the problems of modern physics, and this afternoon's lecture was to be about Einstein's Theory of Relativity. Well, that might be something!

But since the velocity is equal to the height of the thin rectangle, and the time interval to its base, this product is equal to the area of the rectangle.

Repeating the same argument for each thin rectangle, we come to the conclusion that the total distance covered during the time interval (o,t) is equal to the area of the staircase or, in the limit, to the area of the triangle ABC.