8 : Mechanical advantage
Mechanical advantage has been mentioned briefly earlier in this chapter . It is beyond the scope of this manual to discuss mechanical advantage in detail . For a detailed discussion of mechanical advantage , including useful information on estimating the actual vs ideal mechanical advantage real-world applications , please see Richard Delaney ’ s excellent Physics for Roping Technicians ( 2020 ).
In simple mechanical advantage systems , count the number of legs of rope ( also known as ‘ lines ’) that are either connected to the load or that are connected to a pulley that will travel at the same speed as the load .
In compound mechanical advantage systems , calculate the mechanical advantage in each simple system first ( as above ), then multiply those numbers to calculate the total advantage gained .
Compound mechanical advantage systems can be an excellent way to ‘ step up ’ the amount of advantage from a simple system . Install your most efficient pulley closest to the load – this will ‘ multiply the efficiency ’ throughout the system .
Compound systems are described as ‘ one simple system pulling on another simple system ’.
A significant reduction in actual force will occur due to inefficiency at each pulley or block .
Methods of calculating mechanical advantage assume that rope legs will run parallel to loads and pulleys – separating rope legs will lose mechanical advantage .
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