|LECTURE DEMONSTRATION MANUAL | Instructional Research Lab : ucla physics|
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M.3.5 The Dreaded Bed of Nails
A "volunteer" removes glasses and jewelry and lies on a bed of 4000 nails. A male volunteer can take off his shirt so that his bare skin is against the nails. A plywood sheet is placed over him and several concrete blocks piled on top. The demonstrator then smashes the blocks with a sledge hammer.
Several physics principles are involved here. The force from any one nail is reduced by spreading the weight over many nails. The inertia of the blocks partially protects the person below from the force of impact. The smashing of the blocks absorbs much of the energy of the blow.
Using too few nails in this demo was a form of torture. In the illustration below Roman consul Marcus Atilius Regulus is tortured to death by Carthaginians in about 255 BC. The illustration was painted in about 1415 in Paris.