# Day 17: Ball and Spring Model Lab

*AP Physics C:* I decided to turn the example problems in the first sections of Chapter 4 of *Matter and Interactions* into a lab. Last week, they determined the relationships for adding springs in parallel and in series. So today, we started with this as a warm-up (thanks Rhett for the diagram!):

Then we put that aside and started the lab.

**PART ONE: Determine the diameter of an atom**

Groups were given:

- a small metal bar that had 1 mole of atoms (from Pasco’s Mole Set)
- a balance
- a ruler
- an AP Chemistry periodic table

First, they had to determine which element their bar was made from. Then they had to determine the size of an atom using the materials listed. Lots of great discussion in the groups.

**PART TWO: ****Determine the interatomic spring constant for copper**

I don’t have any lab equipment for stretching a long wire, so we watched the following video (thanks Bruce!) and collected data:

Although the wire in the video is brass, I said we could assume it was made entirely of copper. We also used the diameter of a copper atom from Part One. More great discussion within each group. It’s a tough problem to reason all the way through — lot of steps. And in the end, they get a spring constant which is similar to the springs they used in the series and parallel lab….which blows a few minds. Most kids think the interatomic spring constant should be really stiff.

The warm-up and both parts of the lab took an entire 80-minute block.

*NGSS Science and Engineering Practice 4: Analyzing and Interpreting Data*