Editing Mechanical advantage (section)

== Efficiency ==
Mechanical advantage that is computed using the assumption that no power is lost through deflection, friction and wear of a machine is the maximum performance that can be achieved.  For this reason, it is often called the ''ideal mechanical advantage'' (IMA).  In operation, deflection, friction and wear will reduce the mechanical advantage.  The amount of this reduction from the ideal to the ''actual mechanical advantage'' (AMA) is defined by a factor called ''efficiency'', a quantity which is determined by experimentation.

As an example, using a [[block and tackle]] with six rope sections and a {{val|600|u=lb}} load, the operator of an ideal system would be required to pull the rope six feet and exert {{val|100|ul=lbf}} of force to lift the load one foot. Both the ratios ''F''<sub>out</sub> / ''F''<sub>in</sub> and ''V''<sub>in</sub> / ''V''<sub>out</sub> show that the IMA is six. For the first ratio, {{val|100|u=lbf}} of force input results in {{val|600|u=lbf}} of force out. In an actual system, the force out would be less than 600 pounds due to friction in the pulleys. The second ratio also yields a MA of 6 in the ideal case but a smaller value in  the practical scenario; it does not properly account for [[energy]] losses such as rope stretch. Subtracting those losses from the IMA or using the first ratio yields the AMA. 

=== Ideal mechanical advantage ===
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The ''ideal mechanical advantage'' (IMA), or ''theoretical mechanical advantage'', is the mechanical advantage of a device with the assumption that its components do not flex, there is no friction, and there is no wear.  It is calculated using the physical dimensions of the device and defines the maximum performance the device can achieve.

The assumptions of an ideal machine are equivalent to the requirement that the machine does not store or dissipate energy; the power into the machine thus equals the power out.  Therefore, the power ''P'' is constant through the machine and force times velocity into the machine equals the force times velocity out{{mdash}}that is,
:<math> P = F_\text{in}v_\text{in}= F_\text{out}v_\text{out}. </math>

The ideal mechanical advantage is the ratio of the force out of the machine (load) to the force into the machine (effort), or
:<math>\mathit{IMA} = \frac {F_\text{out}} {F_\text{in}}. </math>
Applying the constant power relationship yields a formula for this ideal mechanical advantage in terms of the speed ratio:
:<math>\mathit{IMA} = \frac {F_\text{out}} {F_\text{in}} = \frac {v_\text{in}} {v_\text{out}}.</math>

The speed ratio of a machine can be calculated from its physical dimensions. The assumption of constant power thus allows use of the speed ratio to determine the maximum value for the mechanical advantage.

=== Actual mechanical advantage ===
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The ''actual mechanical advantage'' (AMA) is the mechanical advantage determined by physical measurement of the input and output forces. Actual mechanical advantage takes into account energy loss due to deflection, friction, and wear.

The AMA of a machine is calculated as the ratio of the measured force output to the measured force input,
:<math>\mathit{AMA} = \frac {F_\text{out}} {F_\text{in}},</math>
where the input and output forces are determined experimentally.

The ratio of the experimentally determined mechanical advantage to the ideal mechanical advantage is the [[ mechanical efficiency]] η of the machine,
:<math> \eta =\frac\mathit{AMA}\mathit{IMA}.</math>