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==='''Linear motors'''===
 
==='''Linear motors'''===
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A muscle is a linear motor.  Most man-made motors are not linear, since they take advantage of the wheel, a device not possible in animals.  A man-made machine using a linear motor is the magnetic railway, where a magnetic field both lifts the train off the track, and provides a linear thrust.  If we accept the fossil record, the muscle machine preceded electric motors and internal combustion engines, and indeed the also very modern invention of the wheel, by 70 million years.
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A muscle is a linear motor.  Most man-made motors are not linear, since they take advantage of the wheel, a device not possible in animals.  A man-made machine using a linear motor is the magnetic railway, where a magnetic field both lifts the train off the track, and provides a linear thrust.  If we accept the fossil record, the muscle machine preceded electric motors and internal combustion engines, and indeed the also very modern invention of the wheel, by 70 million years.
 
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:::::'''Fig. 4.3 Sliding filaments in muscle'''
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:::::The sarcomere can normally contract to 44% of its fully stretched length. At its optimal length of 2.2 µm, the thin filaments are maximally in apposition with the crossbridges of the thick filaments.
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==='''The force of a muscle depends on sarcomere length'''===
 
==='''The force of a muscle depends on sarcomere length'''===

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