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Ideal Mechanical Advantage (IMA)- estimated mechanical advantage without taking
into consideration any friction loss in the system. When we refer to a pulley system as
3:1, 5:1, 9:1 and so forth, we are referring to the IMA.

Theoretical Mechanical Advantage (TMA)- refers to the mechanical advantage that
has some calculation of efficiency losses, however it not measured.

Actual Mechanical Advantage (AMA)- measured mechanical advantage that will be
actually experienced or observed when friction loss is taken into account.

Within a pulley system, travelling pulleys move toward the anchor when the system is
being pulled on to move a load. The pulleys which remain fixed and do not move when
a pulley system is being pulled upon are known as stationary (fixed) pulleys (Figure
171). As a pulley system is employed to move a load it will collapse to the point where
one or more travelling pulleys will make contact with a stationary pulley. This results in
not being able to move the load any further. The pulley system is then re-expanded,
through a reset, to the original size or throw distance, so that hauling may continue.

Figure 171- Simple pulley system. Simple 2:1 MA with change of direction

Haul Prusik- the Prusik closest to the load which serves to attach the pulley system to

the main line going to the load (e.g. Prusik initially extended to achieve maximum throw
distance).

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