“The Advantage of Pulleys” Demonstration
The lifting force required to raise a load depends upon the lifting ‘tackle’, i.e. the number of pulleys in the sheave blocks at the hook and head of the lifting tackle or crane.
The mechanical advantage is indicated by the number of falls of rope or string between the upper and lower sheave blocks.
The following lists the properties of each lifting device in the demonstration from left to right:
- Direct Lift: Rope falls = 1, Hoisting force = W
- Side-by-side Pulleys: Rope falls = 4, Hoisting force = W/4
- Side-by-side Pulleys: Rope falls = 6, Hoisting force = W/6
- Parallel Pulleys: Rope falls = 6, Hoisting force = W/6
W = Load (negating friction)