Lifting a weight up and bringing it down: work done

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SUMMARY

The discussion centers on the concept of work in physics, specifically addressing the scenario of lifting a weight and returning it to the same position. It establishes that while the formula for work is displacement times force, the work done in this case is zero due to zero net displacement. However, it highlights the complexity of work as a path function, particularly in thermodynamics, where work can be influenced by the path taken. The conversation also touches on the implications of conservative versus non-conservative forces, emphasizing that the energy involved in raising and lowering an object may not equate to the work done on it, especially in biological contexts like muscle activity.

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  • Understanding of basic physics concepts, particularly work and energy
  • Familiarity with thermodynamics, including path functions
  • Knowledge of conservative and non-conservative forces
  • Basic principles of biomechanics related to muscle function
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  • Explore the principles of conservative and non-conservative forces in detail
  • Study the concept of work in thermodynamics, focusing on path functions
  • Investigate the biomechanics of muscle work and energy expenditure
  • Learn about the implications of work-energy principles in practical applications
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Physics students, educators, and professionals in fields such as biomechanics, engineering, and thermodynamics who seek to deepen their understanding of work and energy concepts in both theoretical and practical contexts.

crm07149
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If work is displacement times force, lifting a weight up and bringing it down to the same spot would have zero displacement, and thus zero work is done.

However, isn't work a path function? In thermo we learned that heat and work were path functions while quantities such as internal energy and enthalpy were path functions.

So by thermo reasoning, the work done in the case described above would NOT be zero since work is a path function, but the definition of force as displacement times force says it would be zero.

What am I missing here? Would the same reasoning apply to running around a track, where the person ends at the same spot as they started? Thanks!
 
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Gravity is a conservative force, so the net work around any closed path is 0. The same is not true of non-conservative forces.
 
The energy involved in raising and lowering may not be equal to the work done ON that object. This is particularly relevant when muscles are involved. Work Done 'ON' is not a very relevant factor in many practical instances.
 

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