1. Conservative and Non-Conservative Forces
Hey—where did the energy go?
§ 6.6

2. Poll Question
The piglet has a choice of three frictional slides to descend. Along which slide would gravity do the most work on the piglet? A B C
The wgrav is the same for all. 2

3. Poll Question
The piglet has a choice of three frictional slides to descend. Along which slide would friction do the most work on the piglet? A B C
The wf is the same for all. 3

4. Poll Question
The piglet has a choice of three frictional slides to descend. Along which slide would the piglet have the greatest final speed? A B C
The vf is the same for all. 4

5. Classes of Forces Conservative forces Non-conservative forces
maintain mechanical energy (U + K)
Non-conservative forces
change mechanical energy

6. Conservative Force Path independence Position dependence
The work done by a conservative force on a body moving from Point A to Point B is:
The same along every path from A to B.
Zero along every closed path (loop).
Position dependence
A conservative force is the rate of change of potential energy with position.

7. Question The force of gravity F = mg is: Conservative.
Non-conservative.

8. Question The force of a Hooke’s law spring F = –kx is: Conservative.
Non-conservative.

9. Question The force of kinetic friction F = mkN is: Conservative.
Non-conservative.

10. Question The force exerted by a motor is: Conservative.
Non-conservative.

11. Conservation of Energy
Non-conservative work changes mechanical energy.
E1 = E2
K1 + U1 + Wnc = K2 + U2