the-BA : Did it fray...?

A boat slips its moorings and drifts away. The owner’s insurance company wants to know if the cause was neglect or sabotage. Was the rope worn through by rubbing against something? Or was it old and rotten, so it snapped under tension? Maybe rats or mice gnawed through it. Or was the rope deliberately cut? A clean cut would be rather obvious, but suppose the saboteur thought of that, so used a saw instead?

Have you ever wondered how to distinguish between cut, sawn and snapped materials?

You might like to …

• compare the ends of various solid materials that have been cut with a sharp blade, sawn or snapped by force; look for any distinguishing marks or features that could give clues about which method was used
• investigate the effects of snapping a solid in different ways, for example hitting it hard, bending in one direction, bending repeatedly back and forth, or pulling; again, look for tell-tale signs on the broken end (Caution: Beware flying fragments when breaking a material)
• apply your tests to ropes; compare different methods of breaking, and different types of rope, for example hemp and nylon; you will need to study the broken fibres more closely
• study ‘Exhibit A’, a broken rope, to decide how it became broken (your teacher or technician must know how it was broken, but you must not); carefully explain how you come to your conclusion; your evidence must stand up in court, and should be backed up with other samples for comparison to prove your point.

Image courtesy of www.FreeFoto.com

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