Mechanical advantage

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In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force or torque applied to it. Generally, the mechanical advantage is defined as follows:

For an ideal (frictionless) mechanism, it is also equal to:


For an ideal machine, the two equations can be combined, indicating that the force exerted IN to such a machine (denominator of first ratio) multiplied by the distance moved IN (numerator of second ratio) will equal the force exerted OUT of the machine multiplied by the distance moved OUT (i.e., work IN equals work OUT).

As an ideal example, using a block and tackle with 6 ropes, and a 600 pound load, the operator would be required to pull the rope 6 feet, and exert 100 pounds of force to lift the load 1 foot. Both equations show that the MA is 6. In the first equation, 100 pounds of force IN results in 600 pounds of force OUT. The second equation calculates only the ideal mechanical advantage (IMA) and ignores real world energy losses due to friction and other causes. Subtracting those losses from the IMA or using the first equation yields the actual mechanical advantage (AMA). The ratio of AMA to IMA is the mechanical efficiency of the system.

Contents

Types

There are two types of mechanical advantage: ideal mechanical advantage (IMA) and actual mechanical advantage (AMA).

Ideal mechanical advantage

The ideal mechanical advantage (IMA), or theoretical mechanical advantage, is the mechanical advantage of an ideal machine. It is calculated using physics principles because no ideal machine actually exists.

The IMA of a machine can be found with the following formula:

where

Actual mechanical advantage

The actual mechanical advantage (AMA) is the mechanical advantage of a real machine. Actual mechanical advantage takes into consideration real world factors such as energy lost in friction.

The AMA of a machine is calculated with the following formula:

where

Simple machines

The following simple machines exhibit a mechanical advantage:

  • The beam shown is in static equilibrium around the fulcrum. This is due to the moment created by vector force "A" counterclockwise (moment A*a) being in equilibrium with the moment created by vector force "B" clockwise (moment B*b). The relatively low vector force "B" is translated in a relatively high vector force "A". The force is thus increased in the ratio of the forces A : B, which is equal to the ratio of the distances to the fulcrum b : a. This ratio is called the mechanical advantage. This idealised situation does not take into account friction. For more explanation, see also lever.

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