## Wednesday, December 2, 2015

### For Afternoon classes

Happy Wednesday! Who's got it today?!

Watch and take notes on a video about potential wells. These are represented by graphs of potential energy, U, as a function of position, x.

The way to interpret this is to imagine a particle stuck at the origin of the graph, and then a second particle is moving around at different distances. The graph plots out the energy between the two particles at those separations.

On a U-x graph, we can also identify two types of equilibria - stable and unstable. Stable would be at the bottoms of dips, and unstable would be on hilltops of these graphs. Remember, Nature seeks lowest energy states.

Mathematically, we will be using the new gradient concept, F = -dU/dx. Force graphs can be drawn based on what the slopes are doing on the potential energy graph. Remember, dU/dx = slope of the energy graph!

After the video, you can get working on the spring lab. We are interested in measuring the stretch caused by different masses. The main product of the lab will be the graphs of F vs. x, where x = the stretch distance, or displacement, of your springs.

For homework, complete any parts of the lab that remain, and also write up a short summary of an article you find interesting. Thanks!