Falls are generally divided into short falls and long falls from a height. Long falls include e.g. falls from a balcony, a tree or a parachute fall where the chute does not open. It is easy to conceive of long falls being fatal. Short falls generally occur on the ground outdoors or within the confines of a room, and the human mind has difficulty comprehending that short falls can be fatal. Short falls can indeed be fatal, as documented in the accompanying article by Chang et al. ^{Reference Chang, Elliott-Benjamin, He and Zhang1} The commonest injuries were contusions and hemorrhages. While death is not often instant, it follows due to accumulation of two fluids: blood and brain edema. The authors find subdural, subarachnoid and intraparenchymal types of hemorrhage.

The human head weighs roughly 5 kg (11 pounds), and the energy imparted to the head in a fall depends on the strike velocity and the softness of the contacting surface. The strike velocity v is higher than one might expect, and is easily calculated from the height h and the acceleration of gravity a by the equation v² = 2ah. Counterintuitively, a 12-inch (30 cm) fall already gives rise to a strike velocity of >5 mph (8 km/h), whereas a 44-inch fall gives a strike velocity of >10 mph or 16 km/h. We walk comfortably at about 3½ mph or 5 km/hr, and thus a 44-inch fall is like running into a wall at 3 times the walking speed.

Falling over can kill as well. This happened to the actress Natasha Richardson and actor Gary Coleman. Children can fall to their deaths from heights of <1 m. ^{Reference Plunkett2} Falling over adds to the strike velocity because the body is not only falling but rotating around a fulcrum, the feet. The physics of this was well reviewed in human pathology in a seminal article on contrecoup by Dawson et al. ^{Reference Dawson, Hirsch, Lucas and Sebek3} The accompanying article adds to our knowledge about the lethality of falls from the point of view of forensic pathology, where the lethality filters the input. In our minds, we filter falls according to imagined scenarios, not the lethal consequences, and we often underestimate falls as lethal occurrences.