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What we have created is basically a rope pulley system (obviously, without the pulleys).
This system is sometimes known as a trucker's hitch, and it is used to apply tension in a rope in order to secure heavy loads. However, in the video, I use the system to generate an advantage in order to tow my van.
Pulley systems allow you to trade force for distance, thus gaining a mechanical advantage.
The truckers hitch used here, is equivalent to using two moveable pulleys on a free axle (the two loops of rope) and a fixed pulley on a fixed axle (the tree or post).
In a frictionless world, this would yield a mechanical advantage of 3 (effectively increasing the force of my pull by three), but also meaning I have to travel 3 times as far as my van does.
However, we do not live in a frictionless world, and the friction in the trucker's hitch system is further increased by the fact it does not actually use pulleys, but relies onto the rope sliding into other loops of rope.
This generates a fair amount of friction and - to be perhaps on the slightly conservative side- I thus estimate the mechanical advantage yielded to be slightly over two. This will obviously vary depending on what type of rope is used (some will generate less friction than other).
Friction generated by a rope on a rope is generally not a good idea, and this will eventually weaken your rope considerably. However, for the purpose of an emergency, this sytem will do fine, and it can help you get out of a tight spot. Keeping a rope in your car is a far cheaper alternative than having to call someone to tow you out (and obviously, if another car happens to pass by, the rope can also be used to set up a tow between the two cars).
This system is sometimes known as a trucker's hitch, and it is used to apply tension in a rope in order to secure heavy loads. However, in the video, I use the system to generate an advantage in order to tow my van.
Pulley systems allow you to trade force for distance, thus gaining a mechanical advantage.
The truckers hitch used here, is equivalent to using two moveable pulleys on a free axle (the two loops of rope) and a fixed pulley on a fixed axle (the tree or post).
In a frictionless world, this would yield a mechanical advantage of 3 (effectively increasing the force of my pull by three), but also meaning I have to travel 3 times as far as my van does.
However, we do not live in a frictionless world, and the friction in the trucker's hitch system is further increased by the fact it does not actually use pulleys, but relies onto the rope sliding into other loops of rope.
This generates a fair amount of friction and - to be perhaps on the slightly conservative side- I thus estimate the mechanical advantage yielded to be slightly over two. This will obviously vary depending on what type of rope is used (some will generate less friction than other).
Friction generated by a rope on a rope is generally not a good idea, and this will eventually weaken your rope considerably. However, for the purpose of an emergency, this sytem will do fine, and it can help you get out of a tight spot. Keeping a rope in your car is a far cheaper alternative than having to call someone to tow you out (and obviously, if another car happens to pass by, the rope can also be used to set up a tow between the two cars).
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[[Video(http://insertlinkhere.com, {width:425, height:350})]]using a long rope (100'+), tie one end to car, wrap other end 3 times around a tree 90' away. one person tensions and holds the rope looped on the tree (creating a friction lock). 2nd person goes to the midpoint of the rope and pulls on the rope *perpendicular* to its length (deflecting it from straight). the 2nd person has a very large mechanical advantage: 0.5 sin(x) / (1-cos(x)) is the mechanical advantage, where x is the number of degrees the rope is deflected. for example with a 100' length, the middle person can deflect the rope 10' (about 6 degrees), this pulls the car 1' with a 10x mechanical advantage. your mechanical advantage is reduced the more the rope is deflected, but the 1st person should be able to quickly take up the slack on their end so the process can be repeated.