Lifting a weight up and bringing it down: work done

1. May 13, 2012

crm07149

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!

2. May 13, 2012

Staff: Mentor

Gravity is a conservative force, so the net work around any closed path is 0. The same is not true of non-conservative forces.

3. May 14, 2012

sophiecentaur

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.