Research reaches breaking point

A report in the New Journal of Physics describes how spaghetti lubricated in olive oil is shedding light on why knotted ropes or strings snap where and when they do.

‘Finding the breakage point on a rope with some degree of accuracy is very difficult. Materials like nylon break so fast that it is impossible to see where or why a break occurs, even with a high velocity camera,’ said Dr. Giovanni Dietler of the University of Lausanne in Switzerland. ‘Instead, the best material to see a breakage turns out to be well cooked spaghetti.’

Mountaineers, sailors and anglers know that knotted ropes break easily near to the site of the knot. By looking at why a rope or string breaks at that site, it is hoped that stronger fabrics can be produced to overcome this problem.

The researchers, based at the University of Lausanne and at Poznan University of Technology in Poland, analysed consecutive frames of film to see where the breaking process begins.

They found that the breaking point was localised at well-defined points close to the entrance to the knot, where the spaghetti was very bent.

The researchers then carried out computer simulations of tightening knots to see what effect this had.

‘It was found that the breakage occurred where the bend in the filament was the greatest,’ said Professor Piotr Pieranski of Poznan University in Poland.

Knowing that the higher the curvature in the rope, the more chance there is of it breaking can lead to producing materials with new weaving patterns that reduce the curvature.

This same principle could also be applied to produce stronger plastics by minimising the curvature in polymer chains or by avoiding knots within the molecule.

‘By comparing localisation of breakage points in knotted spaghetti with those reported in molecular simulations of knotted individual polyethylene chains, we were struck by the conservation of the same basic physical principles from macro to nano scale,’ said Dr. Andrzej Stasiak from the University of Lausanne.