School of Physics Lecture Demonstration Manual

Mo-1 Bed of Nails

Published: Tuesday 05 June 2007 - Updated: Thursday 24 March 2011


To demonstrate the essential difference between pressure and force by distributing the lecturers weight over a bed of nails.



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Bed of Nails

Balloon Buster


Bed of Nails


This demonstration illustrates that the distribution of a weight over a large enough area reduces the pressure below the piercing breakpoint of the skin. The apparatus consists of a specially constructed bed of approximately 900 nails evenly spaced on a 1cm X 1cm grid. It is recommended that the lecturer places two chairs either side of the bed of nails and initially supports his weight via these chairs. Once he has carefully positioned his feet on the bed of nails he may release his grip from the chairs easing his weight slowly onto the nails. Initially the force required to burst a single balloon may be found. This is compared to the case where the lecturers weight is distributed over about 300 nails.

Safety notes

Sharps Safety 


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