Forces experienced by falling people

When people hit the ground after a long fall, they tend to get hurt. If they fall a great distance, they are usually hurt very seriously. One scientific study has found that the threshold for human survival is a the pressure on impact less than 50 pounds per square inch.

1. Convert this threshold to metric units: Newtons per square centimeter
2. Pick one member of your group: suppose it lands flat on its back. What is the total area over which the impact will occur?
3. What total force corresponds to the threshold for survival?

Consider this account of a real fall.

"[O]n the frigid 23rd of March, 1944, ... Flight Sergeant Nicholas Alkemade, an RAF rear gunner [had his bomber set afire] by a German night fighter on a raid over Hamburg. [H]e found that he was unable to reach his parachute, stowed forward in the flaming fuselage. Deciding he didn't care to burn alive, he jumped without a parachute just as the aircraft exploded above him. His altitude was 18,000 feet. Falling at a terminal velocity of about 120 mph during this 3 1/2 mile fall (which lasted about 90 seconds), he struck the snowy branches of a pine forest and then landed in less than 18 inches of snow, only twenty yards from bare open ground. Incredibly, his only reported injuries consisted of superficial scratches and bruises, and burns received prior to the jump."

4. What was Sgt. Alkemade's velocity just before he hit the snow?
5. Assume that his acceleration through the snow was a constant size. What was his acceleration?
6. How long did it take him to move through the snow?
7. Estimate Sgt. Alkemade's change in momentum.
8. Estimate the total force on Sgt. Alkemade.
9. Should he have survived?

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.