is used up, another batch is promptly supplied. Just like the train, our cells hum along smoothly when the amount of energy that is provided is equal to the amount of energy needed to function. Now it’s the second day of your grandfather’s new job. A few minutes after the first delivery of coal, he gets a surprising knock on the door. More coal. He thinks, Well, it’s a bit early, but that way I’ll have some extra. He sets it aside next to the furnace. A few minutes later, another knock. More coal. And another. The knocks keep coming, and the coal keeps being delivered. ‘I don’t need all of
...more
