A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have high tensile strength and can be used for dragging and lifting. Rope is thicker and stronger than similarly constructed cord, string, and twine.
Construction
Rope may be constructed of any long, fibrous material (e.g., rattan, a natural material), but generally is constructed of certain natural or synthetic fibres. Synthetic fibre ropes are significantly stronger than their natural fibre counterparts, they have a higher tensile strength, they are more resistant to rotting than ropes created from natural fibres, and they can be made to float on water. But synthetic ropes also possess certain disadvantages, including slipperiness, and some can be damaged more easily by UV light. Common natural fibres for rope are Manila hemp, hemp, linen, cotton, coir, jute, straw, and sisal. Synthetic fibres in use for rope-making include polypropylene, nylon, polyesters (e.g. PET, LCP, Vectran), polyethylene (e.g. Dyneema and Spectra), Aramids (e.g. Twaron, Technora and Kevlar) and acrylics (e.g. Dralon). Some ropes are constructed of mixtures of several fibres or use co-polymer fibres. Wire rope is made of steel or other metal alloys. Ropes have been constructed of other fibrous materials such as silk, wool, and hair, but such ropes are not generally available. Rayon is a regenerated fibre used to make decorative rope. Successive layers are twisted in opposite directions so that the rope resists unlaying when placed under load. The twist of the strands in a twisted or braided rope serves not only to keep a rope together, but also enables the rope to more evenly distribute tension among the individual strands. Without any twist in the rope, the shortest strand(s) would always be supporting a much higher proportion of the total load.
Size measurement Because rope has a long history, many systems have been used to specify the size of a rope. In systems that use the inch (Imperial and US customary measurement systems), large ropes over 1 inch (25.4 mm) diameter – such as those used on ships – are measured by their circumference in inches; smaller ropes have a nominal diameter based on the circumference divided by three (as a rough approximation of pi). In the metric system of measurement, the nominal diameter is given in millimetres. The current preferred international standard for rope sizes is to provide the mass per unit length, in kilograms per metre. However, even sources that otherwise use metric units may still give a "rope number" for large ropes, which is the circumference in inches.
Use
Rope has been used since prehistoric times. It is of paramount importance in fields as diverse as construction, seafaring, exploration, sports, theatre, and communications. Many types of knots have been developed to fasten with rope, join ropes, and utilize rope to generate mechanical advantage. Pulleys can redirect the pulling force of a rope in another direction, multiply its lifting or pulling power, and distribute a load over multiple parts of the same rope to increase safety and decrease wear. Winches and capstans are machines designed to pull ropes. Knotted ropes have historically been used for measuring and performing mathematical calculations. For example, Ancient Egyptian rope stretchers used knotted ropes to measure distances, medieval European shipbuilders and architects performed calculations using arithmetic ropes, and some pre-colonial South American cultures used quipu for numerical record-keeping.
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