Workout: Spring potential energy

Read

Read the web page: Spring potential energy

Launch

To give you some practice on converting forces to energies, go to the PhET simulation Hooke's law simulation to perform a few tasks.

Set up

Choose the "Intro" (on the bottom of the screen) and turn on all of check boxes in the options box at the upper right. Set the Spring Constant to 300 N/m. Set the applied force to the Applied Force to 50 N. Your screen should look like the figure shown below.

Answer these questions

1. Two arrows are shown above the ring, a red arrow and a blue arrow. What object is the red arrow acting on and what object is the blue arrow acting on? 
2. Explore how the spring responds to different values of the spring constant and the applied force. For a given applied force, what happens if you make the spring constant bigger? Is this what you expect? Why? 
3. Now select the tab marked "Energy" in the black bar at the bottom of the page. Turn on all the square check boxes in the options box at the upper right and select "Force plot". Explore what happens to the plot and to the spring as you change the spring constant. Grab the ring with your mouse and be clear how the displacement and force graph and physical representation are related. 

Now turn on the box marked Energy. This shows the area under the curve. As you slide the displacement back and forth, you will see the area under the curve (shown in blue) and the potential energy bar (at the left) move together. Explain why the PE is related to the area under the curve in the Force/Displacement plot.

4. Notice that when the displacement becomes negative, the potential energy bar still goes back positive. Is this an error? Are they just showing the magnitude of the PE? Or is it correct that the PE should still be positive? Explain.

Joe Redish, Fall 2016