Quick questions on Mechanical advantage in pulley systems: HSC Engineering Studies Lifting Devices

Mechanical advantage (MA) is the ratio of load force to effort force.

Single fixed pulley. Changes direction only. IMA = 1, VR = 1. Effort equals load.

Real pulleys have friction in the bearings and rope bending stiffness. Efficiency drops as the number of pulleys increases (more bearings, more bends). Typical efficiency:

Tower cranes on Sydney CBD construction sites use jib hoists with 2-fall or 4-fall configurations depending on the lift weight. Mining draglines use single-fall and double-fall configurations on bucket-hauling ropes. Manual block-and-tackle systems are still used in arborist work, sailing and theatrical rigging.

Changes direction only. IMA = 1, VR = 1. Effort equals load.

Two rope segments support the load. IMA = 2, VR = 2. Effort is half the load; rope travels twice the load distance.

A fixed block and a movable block, each with one or more pulleys. The IMA equals the number of rope segments supporting the load block, not the total number of pulleys.

Two or more separate block-and-tackle systems in series. The overall IMA is the product of the individual IMAs.

Ideal mechanical advantage assumes zero friction. Actual mechanical advantage accounts for losses. The difference is efficiency.

If you reduce force by a factor of 4, you must move the effort 4 times as far. Energy is conserved (less losses).

In any ideal pulley system, VR = IMA. They diverge only when you add losses, where AMA < IMA = VR. :::