How to Configure Block & Tackle

A two-pulley block

Pulleys are generally used for lifting, especially when combined in "blocks," in which a series of pulleys share the same axle. Two blocks used in conjunction can reduce the amount of force required for a lifting task. One block attaches to some immobile support while the other attaches to the load. Because the line, or "tackle," threads backs and forth between the two blocks, you have to pull the tackle a great distance to bring the blocks together a small distance. The payback for the extra pulling length is that less force is needed to lift the load.

Things You'll Need

• Two multiple-pulley blocks
• Line, string or rope

Instructions

1. Attach one of your two multi-pulley blocks to the load to be lifted. (The double-pulley blocks listed in Resources have eyelets to attach to the load.)

2. Attach the second pulley block to a stationary support, preferably directly above the load if you're lifting it vertically. That way no force is wasted on lateral tension. This is also why the pulleys are in a block instead of spread out: to avoid wasted energy through lateral tension. Denote the load end of the tackle End A and the pulling end End B.

3. Thread End A over one of the pulleys in the hanging block. Pull the end down to the load-attached block and thread it under one of the pulleys in that block.

4. Continue threading End A up and down, over the hanging block's pulleys and under the load-attached block's pulleys, until each pulley has tackle running through. Then pull End A to the opposite block again and knot it to the unused eyelet. (The blocks in Resources have two opposite eyelets for this purpose.)

5. Lift the load by pulling End B.

Tips & Warnings

• The more pulleys per block you use, the more you'll thread the line back and forth, and therefore the less force you'll need to input. If the load is to be lifted one meter, then the load-mounted block must also rise one meter and the distance between the two blocks must shorten one meter. If the tackle runs four times between the two blocks, End B must be pulled out four meters to shorten the four runs of tackle one meter each. Obversely, the force needed to lift the load drops by 75 percent.

References

• "Physics for Technical Students"; William Ballantyne Anderson; 1914

Resources

• Honey Brothers: Double-Pulley Block
• Camp USA: Double-Pulley Block