In Poe's famous horror tale, The Pit and the Pendulum, the hero, who finds himself strapped flat to a horizontal surface, notices an almost motionless pendulum hanging from the ceiling 12 m above him. After some time, he also realizes that the pendulum is descending very slowly toward him with, according to the story, the amplitude of the swings and the speed at the lowest point in each swing both increasing inexorably. What is swinging is in fact a small razor-edged crescent of steel which will eventually sweep across the man's heart.
Let's analyze this terrifying situation more closely to see if Poe's spell-binding description actually makes physical sense. To do this, we must make some assumptions which