Non-conservative forces and Power

Non-conservative forces and Power

The work done by a non-conservative force does depend upon the path taken. Friction, for example, does less work on a book dragged across a table if the book is dragged straight across than if the book is dragged in a curved path.
The conservation laws obeyed by conservative forces (such as gravity) are broken by non-conservative forces. For example, the equation of conservation of Mechanical Energy
```
       KE(final) + GPE(final)  =  KE(initial) + GPE(initial)
```
becomes
```
       KE(final) + GPE(final)  =  KE(initial) + GPE(initial) + W(nc)
```
where W(nc) is the work done by non-conservative forces.

Power is the rate at which work is done, or energy is spent:

                             work       (Joules)
                 Power   =  ------      -------- = Watts
                             time       (second)

One watt is a tiny amount of power; ordinary light bulbs produce 60 or 100 Watts.

Viewgraphs

Answer to the puzzle of the block-and-plank clock: