We began today with a series of demonstrations that together, will help students to conceptualize the “Normal” Force. First up was a very nifty contraption which shows that even small forces do in fact, move a wall (Jon said that this even works with a brick wall!)

Jon attached a metal rod to the wall with modeling clay. Between the table an the rod, he placed a T-pin his Biology teachers unknowningly provided to him. Glued to the T-pin is a small piece of mirror. A few feet away, they had a laser set up, which was pointed at the mirror. As you push on the wall, the wall moves, which causes the bar to roll the mirror, which in turn changes the reflection of the laser. Students can see the effect of you pushing on the wall by watching the laser dot on the opposite wall move up and down. {Hopefully that made sense.} Here’s a picture of the setup:

*I guess Jon didn’t want to bring his hovercraft from Minnesota, how rude*}

*Modifications Jon made to the procedure:*

*Blue tarp works fine, don’t need that pattern of holes – he just put 30 small triangular holes throughout*

*Duct tape around between small disc and big disc*

*Use the biggest fender washer @home depot you can find instead of the coffee lid*

*Make the hole (at the very end) as close to the size of shopvac nozzle as you can (need a tight seal)*

^{st}yt students)

{chris inserts a week or two of material from the math modeling curriculum to review trig concepts.}

{does math review before this unit not at beginning of the year like most teachers}

After completing the worksheet, we whiteboarded our results.

Notes from WB:

(Acting as students saying that cos is always the horizontal component of a vector)

- What on the diagram will be equal to the Vertical leg? (Answer: weight)
- What will be equal to the Horizontal leg? (Answer: T1)
- Based on triangle, which should be the bigger force? (Since vert. leg>horizontal leg, Weight)
- Does you answer match that fact?

{

*Which in looking through my copy looks like #26 in chapter 4*}

If floor is frictionless, how does he push the broom?

http://xkcd.com/669/

If running short on time – have all students display boards, then ask if anyone has questions.

Address the questions as needed, and move on.

(Jon mentioned that Steiner (sp?) has variations of worksheets in the modeling website, probably under password wall for those that attended the workshop)

^{st}Trial- both cars moving with equal mass & approx same speed

^{nd}Trial – add standard masses to one car, so the collision has uneven mass

^{rd}Trial – One stationary vs one moving

^{th}Trial – One moving fast, the other slow

^{th}Trial – Cars start together and explosion with cart “spring”

{Obviously (?) you could keep going if you feel the need

**What we liked**:

^{rd}law

^{rd}law

**What we didn’t like**:

(Demos are good, but students are watching not doing)

{someone mentioned possibly using force table labs to introduce 2D/trig}

to get his kids ready for it.

**Unit V: “Atwood Machine” with vernier track**

From there, we started the next unit. Here’s what each end of the track looked like (the middle is just a track)

** **

Jon changed the first question slightly:**What factors will effect the motion**? (between letting go of the cart and hanging mass hitting ground)

**What factor effects the cart’s acceleration?**

*Angle of the track – ?*

*Starting speed -?*

*Chris showed us a quicker way of working through the process by guiding us to eliminate the factors mentioned that cannot be adjusted (Mass of Earth) or that could be removed with creative lab design. The last two options we left open, that depending on your class, you may or may not want to divide and conquer.*}

**Purpose**: What is the graphical & mathematical relationship that exist between the mass of the cart and the force that is accelerating it.

- Keeping the mass of the hanger while adding mass to the car
- Using photogate(s) above the track instead of motion detector
- Variation of this option is to attach picket fence to cart the cart and use vernier program
- Using kinematic equations and measure total time with stopwatch for total distance measured
- Having the students predict the mass of the system from data, and then, after showing prediction to the teacher, measuring the mass and comparing results to predictions {I like this!}