After the tour, Chris also mention a book to us that he has stumbled on due to modeling that he has found to be very informative: Preconceptions in Mechanics.

Jon and Chris also mentioned joining the Modeling Association and the American Association of Physics Teachers, as they both have a tremendous amount of materials for physics teachers.

Before we got into the heavy stuff again, Jon also showed us a great website with lots of demos: U of Minn Demos.

From there we began to discuss the lab from the previous day (Hooke's Law Lab). A few of the key points that came up we that we felt that this was great opportunity to discuss the limitations of a model, namely the fact that the spring will not always be a linear relationship. Most groups, due to the strength of the spring also found that the beginning of the plot (near the origin) was also a non-linear relationship. Other important questions the were raised, such as, "Did the length of the spring effect the spring constant?"

If the groups followed traditional graphing protocol, they would have plotted $\Delta x$ vs F, which leads to a great series of questions. What does the slope of the graph represent? What does it mean to have a bigger slope on the graph? How can we manipulate the graph such that an increase in slope means a stronger spring?

You can also possibly delve into significant digits. What is the variation/uncertainty in the applied Force? What would that do to you calculation?

Jon also mentioned, that if you have the resources/equipment, set up the experiment with both the force probe and the motion detector, so even if the spring is bouncing, you can get F vs $\Delta x$ data.

From there, we began working on Unit VII worksheet 2.

A few things to note:

#5 This problem is a great reminder of the graphical derivations from kinematics.

Specifically the derivation of the area when you know the slope of the line

See derivation of $\large \Delta x = v_o t + \frac{1}{2} a \left(\Delta t \right)$

From there Jon tried to create a demonstration, however he was missing some necessary materials. Here's a list of what you need (not what he had):

- 1.5" PVC pipe (Jon uses an 8 ft pipe, but shorter is ok) (clear tube if you can afford it)
- 1/2" drill bit (to make a hole drilled about 2" from one end of the PVC pipe)
- 3/8" hose barb (something like this, may need different size depending on vacuum tubing)
- Teflon tape (wrapped around barb before it is screwed into 1/2" opening in pipe)
- 40 mm Competition Ping Pong Ball (as we saw, the basic/cheap ones won't work)
- 3" packing tape
- Jon also mentioned you may need a coupler on each end for added surface area
- Soda can (with a book on top for added inertia)

{Update 7/13: Here's some pictures and videos taken during today's successful launches)

While he was tinkering to get that to work, one of the cohort near me was talking about a cool demo she does with her class. She gives the kids garbage bags (unused) and asks who can inflate them with the fewest number of breaths. Once the kids are about ready to pass out, she shows them how you can do it with one breath (Here's a great set of resources, if you scroll down until you see pg 13 in bottom right corner, you'll see the explanation.)

Once Jon conceded that he wasn't going to get his demo to work today, we moved on to another lab. The set up was a modified version of Option 1 of the Energy Transfer Lab in the Teacher Notes (see bottom of page 8 of the notes) in which the track was on an incline. By adding this twist, you can show the transfer of energy from elastic to kinetic to gravitational energy.

We again worked through,

**What do you notice? What can you measure?**

Chris then briefly showed us this:

Before continuing with then circling/striking out what we can/cannot manipulate.

From there, we stated the purpose:

To determine the graphical and mathematical relationships that exist between the initial starting position, the launch speed, and the maximum height.

We ended the day experimentally determining the spring constant for the metal loop.

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