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What is a Block and Tackle?
Mary McMahon
Mary McMahon
A block and tackle is a simple but highly effective lifting device, thought to be invented by Archimedes. These systems were used extensively for construction in the ancient world, and continue to be used today for a variety of applications, especially at sea, where non-motorized lifting systems are highly useful. A basic block and tackle includes a single fixed pulley, or block, and at least one additional pulley, linked with rope, to form a complete set. Depending on the size of the load being lifted, additional sets may be used to further distribute the weight.
The engineering of a block and tackle uses pulleys to distribute the weight of a heavy object. By lightening the load, the pulleys make it possible for one person or a small crew to move a potentially very heavy object relatively safely. In a single set, a hook from the free swinging pulley is attached to the object being lifted, and the pulleys are threaded with rope. The user pulls on the free end of the rope until the object has been moved. In more complex systems, the rope may run through a series of pulleys to make the end load even less.
For each additional block and tackle added to the set, more rope must be used. While additional sets can be useful, after a certain point they will create friction, interfering with the easy movement of the lifting system. Thus, assembling a block and tackle system does include some judgment calls, because the user needs to decide how to balance the need to create a lighter load with the extra rope and friction multiple pulleys create. It is also important to have safety measures in place such as belays to prevent the load from falling while it is being lifted.
The mechanics behind a block and tackle involves a force for distance trade. What this means is that, the more involved the pulley system, the longer the rope to work is has to be, translating into more total distance that the user must pull it. However, the force of the user's work is more powerful with a longer rope, because of the weight distribution that it permits. Many other everyday items involve force for distance trade-offs, including things like nail clippers which operate on the lever principle, and car brakes, which use hydraulics.
Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.
Learn more...
Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.
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![A simple rope pulley, part of a block and tackle system.]()
By: ZerborA simple rope pulley, part of a block and tackle system. -
![Several wooden pulleys that are part of a block and tackle system on a boat.]()
By: Philippe LERIDONSeveral wooden pulleys that are part of a block and tackle system on a boat.
Discussion Comments
@BigManCar - I know what you mean. It's always surprising what people come up with when they need to get something done.
This kind of technology was partially responsible for all of the incredible, huge buildings in places like Europe and Asia, which came along well before any kind of crane or other construction equipment.
I love to travel and see historical buildings. It is incredible the level of detail and workmanship that goes into them on any level, but when you think about how little they had to work with technologically, you appreciate it that much more.
What always amazes me about things like this is the fact that somebody had to think it up in the first place.
It is one thing to find new or interesting ways to use something like this, but imagine how smart the person was, thousands of years ago, who sat down and came up with this in the first place. It completely changed the amount of work people were able to do with just human or animal power.
A lever like this can be incredibly powerful if you set it up correctly. When I was in the Army, we would sometimes go on very rough roads, or sometimes in areas with no road at all, in large, heavy trucks. The would get stuck sometimes, and there was no way a tow truck was getting back there.
We had a block and tackle setup with a bunch of ropes and pulleys that you would attach to trees or other heavy things, and then to the stuck vehicle. Get a bunch of guys on the rope, and you could pull it right out. Amazing.
As one of the lower-ranked guys out there, I usually had to put the whole thing back in the bag when we were done. Funny thing was, that usually took longer than pulling out the massive, heavy truck.
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