Rope
From Freepedia
- Rope is also the title of a movie by Alfred Hitchcock
A rope is a length of fibers, twisted or braided together to improve strength, for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength (i.e., it can be used for pulling, not pushing). Common materials for rope include manila, hemp, hair, nylon, and steel. Sometimes woven straps or chains are used where rope could be used, especially in securing loads to vehicles.
Other fibrous plant materials sometimes used include cotton, linen, coconut-husk fiber (coir), jute, and sisal. Other synthetic fibers in use include various forms of polypropylene, polyethylene (e.g. Spectra ® a high modulus polyethylene), aramid (e.g. Kevlar ®), and polyester (e.g. Dacron ®). Some ropes are constructed of mixtures of several fibers or use co-polymer (mixed) fibers.
Rope has been an essential tool since prehistoric times. Today, steel wire rope has largely supplanted fiber rope in heavy construction and industrial applications because of higher tensile strength. Fiber rope is still used extensively in light industry and in activities like sailing and climbing.
In order to fasten ropes, a large number of knots are used. Some rope material, like hemp, is stronger when wet with water.
A pulley is used to convert the pulling force to another direction, and multiple pulleys may be used to increase the mechanical advantage, allowing the pulling or lifting of heavy loads with limited force and strength of rope. Winches and capstans are machines designed to pull ropes.
Contents |
Styles of rope construction
Twisted ropes and hawsers
Twisted rope, also called laid rope, is historically the prevalent form of rope, at least in modern western history. Most twisted rope consists of three strands and is normally right-laid, or given a right handed twist. Large heavy duty ropes are sometimes called hawsers. Twisted hawsers were often made of 4 strands of right laid rope, laid left, or given a left handed twist, this was sometimes called cable-laid. More strands are sometimes used.
Twisted ropes are built up in three steps. First, fibers are gathered and spun to form yarns. A number of these yarns are then twisted together to form strands. The strands are then twisted together to form the rope. The twist of the yarn is opposite to that of the strand, and that in turn is opposite to that of the rope. This counter-twisting helps keep the rope together. Any rope of this type must be bound at its end by some means to prevent untwisting.
Twisted ropes have a preferred direction for coiling. Normal right laid rope should be coiled with the sun, or clockwise, to prevent kinking. Coiling this way imparts a twist to the rope. Braided ropes (and objects like garden hoses, fiber optic or coaxial cables, etc.) that have no lay, or inherent twist, will uncoil better if coiled into figure-8 coils, where the twist reverses regularly and essentially cancels out.
Before modern rope making machines were invented, these ropes were constructed in a rope walk. This was a very long building where strands the full length of the rope were spread out and then laid up or twisted together to form the rope. The cable length was thus set by the length of the available rope walk. (See also the unit of length called cable length.)
Braided ropes for sailing, climbing, and safety
"Laid" or twisted ropes tend to untwist under load causing the load to spin if not otherwise supported. Therefore, ropes used for sailing, climbing, and rescue applications are usually braided to avoid this problem.
Braided ropes can be divided into two primary categories: dynamic ropes and static ropes. Static ropes have low stretch properties. The typically stretch less than 6% under normal loading conditions. They are used for controlling sails and for rappelling, especially in caving because the rope itself is climbed, rather than the rock. They are also used for carrying or hauling equipment and attaching pieces of equipment together. Dynamic ropes are made to stretch as much as 50% of their unloaded length, which is crucial for limiting the maximum force experienced by a climber that falls when using one (and also the maximum force experienced by any piece of gear securing the climber to the rock or ice). The main ropes (called lead ropes when the climber is leading) that a climber uses are dynamic.
Braided ropes are generally made from nylon, polyester or polypropylene and have kern mantle construction. Nylon is preferred for durability and good resistance to ultraviolet light. Polyester is about 90% as strong as nylon but has better UV resistance and less change in length when wet. Polypropylene is preferred for low cost and light weight (it floats on water). Kernmantle ropes have a core (kern) of long fibers in the center, with a braided outer sheath (mantle) of woven coloured fibers. The kern provides most of the strength, the mantle protects the kern and determines the handling properties of the rope (how easy it is to hold, to tie knots in, and so on). In dynamic ropes, the core fibers are usually twisted, and chopped into shorter lengths which makes the rope more stretchy. Static ropes are made with untwisted core fibers and tighter braid, which causes them to be stiffer in addition to limiting the stretch.
Braided ropes without a core have a much lower strength to weight ratio, but are cheaper than kernmantle ropes. Thus, they are used for low cost applications and where strength is less important, such as general utility applications in the home. Braided ropes are made in a wide range of diameters, from 1mm to over 13mm for rescue applications.
How to handle rope
Image:Cordages-mutin.jpg Rope made from hemp or nylon should be stored in a cool dry place. It should be coiled and not twisted. If rope is found to be fraying you can melt some wax onto the end or in the case of nylon rope just melt the end so it fuses together. For fibre rope, fixing frayed ends can be more difficult. A strong twine should be used to lash the frayed end together to produce a whipped rope; this will help the end from coming apart again and make tying knots easier. If a load-bearing rope gets a sharp or sudden jolt or shows signs of deteriorating the rope should be replaced immediately and should be discarded or only used for non-load-bearing tasks.
Punitive uses
- Ropes are also used to tie down punishees, especially for severe corporal punishment
- Furthermore ropes can be used (as so-called pervertibles) as a whipping device, of widely different impact depending on length, weight and whether the target zone is bare; working in knots or hard objects gives at a fiercer bite.
One realizes its potential sting when considering the dreaded cat o' nine tails was usually made of rope, as were the milder knittles. Thus aboard ships, a rope's end was frequently applied as an implement for the lightest on the spot discipline of boy and adult sailors, but considered merely a tangible warning as even a few informal strokes of the bosun's cane for somewhat worse offenders were not deemed worthy of a formal record.
- In the Royal Navy, the terms Bimmy, Teazer, Togey and Sennet whip were all usual for a similar implement for summary discipline used on boys' backsides: a rope of about 18 inches long was dipped in hot tar to make it heavier and brittle, usually with a knot on the striking end (the term 'bull's eye was used when that hit precisely between the buttocks, so either on crack or family jewels, both far more tender then the fleshy mounds) - naughty boys were ordered to bend over on the spot presenting their posterior to be lashed with it for such futiilties as taking to long to get in or out of the bath tub (then still wet and stark naked); however the terms were equally used for a thin whip made for leather shoe laces pleated to a single end
- The rope is also a metonymical expression, as the noose, for capital punishment by hanging.
See also
- Jump rope for rope skipping
- Lashing knot
- Whipped rope
- Ropework
