What Is a Block & Tackle?

What Is a Block & Tackle? image by Photo and drawing courtesy of Wikipedia Commons at http://en.wikipedia.org/wiki/File:Mercator06.jpg
What Is a Block & Tackle? image by Photo and drawing courtesy of Wikipedia Commons at http://en.wikipedia.org/wiki/File:Mercator06.jpg

Overview

A system of multiple pulleys connected to a load by a rope and hook, the block and tackle is a fundamental tool for efficient lifting of heavy objects. This simple rope and pulley device trades distance traveled for force applied.

What Is a Block & Tackle?

Parts

The shackle anchors the device to a stable leverage point and the hook attaches the system to the load. Either pulley assembly is called a block, while tackle refers to the other gear.

Adding Distance

The block and tackle increase the apparent distance the load travels. Lifting is easier, but the total effort is essentially the same because the actual distance is unchanged.

Splitting Force

A typical block and tackle include four times as much rope in the lift as the distance the load is actually moved. The force needed to put the load into motion is one-quarter the force needed for direct lifting.

Simple Hoists

Simple hoists have four to six pulleys split between two blocks. The friction losses of multiple pulleys reduce the overall efficiency of the block and tackle.

Hybrid Hoists

Common modern versions of the old block and tackle incorporate a ratcheting winch and levering handle. Built with metal parts and cable, the modern come-along lifts loads a simple hoist cannot.

References

  • Brittanica Online, Block and Tackle

About this Author

James Young began writing in 1969 as a military journalist combat correspondent in Vietnam. Young's articles have been published in "Tai Chi Magazine," "Seattle Post-Intelligencer," Sonar 4 ezine, "Stars & Stripes" and "Fine Woodworking." He worked as a foundryman, woodturner, electronics technician, herb farmer and woodcarver. Young graduated from North Seattle Community College with an associate degree in applied science and electronic technology.

Photo by: Photo and drawing courtesy of Wikipedia Commons at http://en.wikipedia.org/wiki/File:Mercator06.jpg

Article provided by eHow Home & Garden | What Is a Block & Tackle?