1. Conservative and Non- Conservative Forces Hey—where did the energy go? § 7.3

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? ABC D.The w grav is the same for all.

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? ABC D.The w f is the same for all.

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? ABC D.The v f is the same for all.

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

6. Conservative Force Path independence 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 (–) gradient of a scalar potential energy function.

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

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

9. Think Question The force of kinetic friction F =  k N is: A.Conservative. B.Non-conservative.