Beer bottles are often used as weapons in interpersonal violence. Considering a bottle full of beer or an empty bottle with no beer inside, have you ever thought about which one is likely to cause more injuries?
Stephan Bolliger, Steffen Ross, Lars Oesterhelweg, Michael Thali and Beat Kneubuehl were awarded the Ig Nobel Prize in 2009 for this topic. They tested the breaking energy of some beer bottles in a drop-tower to estimate the breaking energy of the bottles, and whether it exceeded the energy required to cause serious injury to a victim. The results showed that the full beer bottles bursted at energies of 30 J, whereas the empty beer bottles shattered at energies of 40 J. Thus, the empty beer bottles withstood about 10 J more than the full beer bottles before breaking, and these breaking energies surpassed the minimum fracture-threshold of the human neurocranium (14.1 J).
The phenomenon of empty beer bottles breaking at higher energies than full ones can be explained by two factors. Firstly, beer is an almost incompressible fluid. Even a slight deformation of the bottle due to the impact of the steel ball can lead to an increase in the pressure inside the bottle and its destruction. Another factor is that beer is carbonated. This gas can cause the bottle to explode under certain pressure conditions. The gas pressure in the bottle gives rise to an additional strain on the bottle, whereas an empty bottle obviously does not possess these qualities, and externally induced strain on the bottle walls will therefore cause the bottle to break. Thus, empty beer bottles are sturdier than full ones, but both full and empty bottles are theoretically capable of fracturing the human neurocranium. Prohibition of these bottles is therefore justified where there is a risk of human conflict involved.