FIU Modeling Workshop - Day 11

We started today by finishing the modified lab.  After finishing, we all made whiteboards of our results and presented them.

During the presentation, a few ideas came up.  One, the groups that used the motion detector had much better results than those that measured the compression with their eyes.  Two, instead of measuring the spring constant with hanging weights separately, we could attach force sensors to the top of the car and measure the force directly during the launch.  Third, we could use a level app from smart phones to measure the angle of inclination of the track.  Four, we could use video analysis to measure the change in height (although I'm not sure if this would be as accurate as the motion sensor).

In the end, adding an inclined ramp to this lab, definitely increase the level of difficulty.  I think this would be good for a second year class, or possibly AP.  However, I think adding studying 3 forms/modes of energy in one experiment is a bit too much for first year students (especially standard level).

One of the groups placed their energy pie charts on a sketch of their velocity vs time graph, which proved to be a great way of showing the energy relationship (most of us just made a pseudo-motion map with a sketch of the track).

One other piece of advice from Jon was to make sure that you stress energy "transfer" not energy "loss" when discussing friction or other losses of energy due to non-conserved forces.

Jon also mentioned that, surprise-surprise, he had a homemade launcher instead of buying the circular metal spring.  He took a piece of 2x4 and attach two 16 penny nails (far enough apart to rest the track in between the nail).  Once the track is place perpendicular to the wood, in between the nails, he stretches a rubber band (new each lab) between the nails (over the track).  Here's a rough sketch of a top view:


Where the yellow oval represents the rubber band, the blue circles are the nails, the grey rectangle is the track and the brown rectangle is the 2x4.  If you need to keep it level, just add a 2x4 to the other end of the track.

From there we moved to a paradigm demonstration for "potential" energy.  (I have it in quotes as we were told this name can carry with it bad misunderstandings, instead you should just call it gravitational energy or elastic energy, etc.)

Jon said that "energy" can cause pain.  So he had Chris come to the middle of the room (simulating a student from the class).  He told Chris to stick one foot out in front of him, and then asked, "Would you rather me drop this bowling ball (from waist high) or this tennis ball (also from waist high)?"  Obviously we were all cheering for the bowling ball.  Chris then asked, "Would you rather me drop the bowling ball from here (waist high) or from here (just above his shoe)?"  Chris then asked us, do you really need to do anything else to teach $\Delta {E_g} = mg\Delta h$?  Then (just to remind us of the spring equation), he suggested having 2 rubber bands, and basically run through the same thing, which rubber band would you like to have snapped on your arm, and from what distance?

After that we started working on Unit VII worksheet 2b.  Like most of these, we worked individually and then each group was assigned one problem to whiteboard.

During the board meeting we had a great discussion as to exactly how energy flow diagrams and energy bar graphs should depict the drawing.  One part of the group felt that if the type of energy is known, it should be identified (even if the interaction is outside the system); others felt that if it wasn't part of the system, it should not be named.  I'm not sure who "won" the debate, and we basically left it up to each person to use as he/she sees fit in their class.  During the discussing, it was pretty obvious that even the experienced teachers in the room had some misconceptions about energy and what it really means to define a system.  We agreed that this is a tricky concept, and talked about to what level of understanding we should try to get our students.  Is it enough for them to merely identify the types of forces present and just that energy is entering/leaving the system, or do they need to describe the the exact means by which the energy is leaving (form of heat or work).  {My guess is that in the end it depends on your students and the standards/goals for your class}

One thing that came to mind for me was my Thermo I&II teacher who stressed that if it's not important enough to be identified as part of your system, the interaction doesn't deserve a name.  I'm also well aware that my students are not sophomore engineers in a Thermo class but 1st or 2nd year high school students.

We then went on to discuss our reading from last night, Making Work Work.  We did a different style of discussion in which each group wrote down 3 things they felt important within the article and then we shared our thoughts.

We finished the day by wrapping up Unit VII
What worked:
After we go the hang of them, we liked the energy bar graphs and flow diagrams
We liked the lively discussion over worksheet 3b
We liked the chaos/challenges of the last lab (cart on the incline w/spring launch)*
We felt that when Chris showed the graph he expected, we better understood what to do**
We liked struggling through the lab, it gives us a better appreciation for what I students will experience

What didn't work:
We realize that we need to be reading the "readings" provided to the students, so we know what "they know" for each lab.
We felt that the prior knowledge requirements/level was too high for the last lab*
We felt that same lab did not have clearly defined objectives**

* and ** comments show just how split we were for the lab

Jon, Chris, and David Jones (the FIU instructor who helps facilitate this workshop) talked a little bit about the fact that the binder and online resources are not a script we have to follow, rather the tools that have emerged from numerous teachers struggling with this style of teaching.  They encouraged us to use what we liked, and modify or omit what we didn't.  In essence they reminded us that we are professional teachers who know our students and school culture.  One of the great characteristics of the modeling method is how easy it is to adapt things to suit a given school.  As we grow in using some or all of this material, we were encouraged to share our take on it with others, so the material continues to evolve.  Their biggest hope was that we didn't just copy the binder as is and pass it out to our students.  I think the biggest advantage to coming to this workshop is beginning to find how I might use all this resources.  For those merely reading this blog, or the others like it, I strongly recommend you set aside the time and come to a workshop.  One of the foundations for this system is that you have to experience something for yourself to truly learn it, watching or reading about it, simply don't work.  (Yes that includes you Kahn Academy) {sorry, just had to get that in somewhere}

FIU Modeling Workshop - Day 10

At the start of today's class, Chris took us on a tour of the ASU Modeling website.  Most of the important stuff he showed us is password protected.  For those that are reading this that have not attended a workshop, sorry, I can't help you.  Chris showed us some of the math resources he uses to help students with trig/vectors.  Since there are several teachers present that also teach chemistry, Chris showed us some of the chem resources as well.  One thing we discussed was using flame tests or emission tubes to show the quantized model of the atom.  Someone asked about diffraction glasses, so if that person is reading this, go here. Chris also showed us two important inventory tests that we can use as pre- and post-tests to assess our students understanding.  One was the Force Concept Inventory (FCI) (Mechanics) and the other was the TUGK2 test (graphing).

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)

So far Jon hasn't gotten the demo to work, once he does, I'll post pictures/videos.
{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.

FIU Modeling Workshop - Day 9

I missed this day of the workshop, however, a few of my cohort were gracious enough to take notes.  I'm doing my best to take what they gave me.  Any help to clarify things would be greatly appreciated.

The day began with everyone working on Unit VI worksheet.  Everyone worked individually, and then the groups met to create whiteboards.

- Useful to separate horizontal and vertical givens in table:

-Good to explicitly show + state that t is the same for horizontal and vertical motion
-Good to keep algebra in variable until the last step - then plug in number

#4 Would be interesting in adding a horizontal & vertical motion map for car and ball

-stress constant velocity in horizontal direction

- ESL students have difficulty with "how long" thinking it means distance

LoggerPro basket ball shot analysis follow up
- After students have generated data, insert 3 graphs + auto arrange

• x vs t
• y vs t
• $v_x$ vs t
• $v_y$ vs t

-Highlight first 1.5 second to analyze

•  compare slope of x vs t and average value of $v_x$ from $v_x$ vs t graph
• lead students to see that $v_x$ is constant by $v_y$ is changing (slope is 9.8 $m/s^2$)
• If you want, have students insert a quadratic fit onto y vs t graph and lead them to find what the meaning of the constants are in the regressed equation.

Next on the agenda was to split up an article to have summarized on whiteboards by the groups.

After lunch, Jon and Chris asked for feedback for Unit VI
What worked:
Video analysis lab
Plan for Dart Gun for Classic Monkey Problem
Worksheet #3
Wells Reading
Hammer article about Lisa & Ellen
Group Work
Adaptability of labs to every level of student (*response to comment on what didn't work)

What didn't work:
Transition from 1D to 2D - we would like to see the process
Time constraints
Simplicity of labs*

Jon and Chris then started the paradigm lab for Unit VII
Had 3 volunteers

1. Held a bowling ball and walked at constant speed
2. Pushed against a wall
3. Lift a small mass

Group was then asked, "Who is doing the most work?"

Physics defines work in a more specific way

A change in position due to a force that is applied in the direction of the change in position

-Establish direction early on and physics specific definition of work

-Student "1" does no work on the bowling ball

-Pushing a stuck car - you should push parallel to maximize work
-Teach students the concepts before introducing the math

Jon dropped a bowling ball - had cohort brainstorm different types of energy.
Discussed the energy transfer mechanism -> work

"We" then began Unit VII worksheet 1 before doing any labs.  Worked on the assignment individually and then presented a problem on whiteboards.

#3) still has velocity at the top
Discussion of energy as a scalar

Be careful to use "transfer" instead of "lost" when referring to energy

Jon and Chris then used a Piece of equipment with four wooden track, each with a different shape and unique color  (the only similar product I'm finding on the internet is this).

The students are then asked,

1. "Which ball will reach the end of the track first?"
2. "Which will hit the ground the farthest from the table?"

Answer to #1 - ball on the "blue" track  & #2 - all are the same except the "yellow" track



Then moved on to "Spring Lab"
Mass hanging on a spring, which is hanging from the Force sensor
Purpose: To determine the mathematical and graphical relationships that exists between force and displacement of a spring

Each group was given 2 different spring (1 short & 1 long)
{Overall there were 2 different lengths and 2 different spring constants for this lab.} 
{Some groups randomly selected 2 lengths with same k, others had 1 of each k}


Group plotted F vs x  results on whiteboard

FIU Modeling Workshop - Day 8

We began today with a Newton's 3^rd Law demonstration:

Same track set up, with Force sensors attached to the top of each car.  The twist for this demonstration is to use the magnets to apply to force between the two cars and not the direct contact.  There are a couple of things to note for this demonstration.  Have one car against the stopper and start with the second car "far away" from the first car.  Zero both probes, and make sure you reverse the direction for one of them so they both have positive in the same direction of the track.  Have the magnets inside the car so the same pole faces outward and thus repel the cars.  Push the force probe of the second car (not the car itself)

From there, were picked up on the lab with which we finished yesterday.  Before starting the experiment we briefly discussed the merit of breaking the lab groups into different types of investigations, in which we would have 3 different trials: "A" would look at keeping the mass of the cart constant, but adding mass to the hanger; "B" would keep the hanger constant, and add mass to the car; "C" would move mass from the car to the hanger, keeping the mass of the system constant.  In an effort to save time, we have everyone do option "C" but I may or may not look at all the groups (maybe in my honors class?)

Also showing a way to move through the whiteboard process more quickly (as needed by time constraints or if class is not productive in meetings), Jon walked us through a "Circle the wagons" meeting.  In this format, all the groups show their white boards, and the teacher leads the group to try to draw conclusions in looking at all the results at once.

{As we were getting started, Jon also mentioned that when you are "normal" whiteboard meeting after a lab, in subsequent labs, start with a different group each time and change the order you call the groups forward.}

During the meeting, we had a great discussion on whether you should explain/guide to the students before starting the lab that they will need to plot Force vs acceleration so that the slope is mass, or wait until the end.

{My thought is to wait until the end, have all the groups manipulate their graphs, as teacher does it on projected screen}

At this point, Jon showed us a quick follow up demo/lab (used vernier "Lab 9 – Newton’s 2^nd Law")

Jon taped an accelerometer to the force probe (Jon uses Velcro tape at his school).  Then you just click the record data button, and then push the cart back and forth.  Viola, data showing $F \propto a$

           

From there, we started individual work on Unit V worksheet 1 (#'s 1-4) and worksheet 2 (#'s 1-3)

As we got started, we briefly discussed strategies for word problems (w/ forces).  A summary of what we said was:

• Have students sketch what is happening and identify the system with dotted circle/box
• Get the words out of the word problem
• Create a Free Body Diagram
• Next to FBD, draw an arrow showing the direction of acceleration 
• That will be "+" direction for the problem
• This convention will aid circular motion problems later in the year

Notes from whiteboard session:

•  Wkst 2: #2 is a great problem since a given number isn’t use in the calculation, but rather for analysis at the end.
• Wkst 2: #3 mass not given, so students need to determine it from the Weight
• Chris- Make sure units are included in the calculation not just at the end
• Possibly change wording of problem since the normal force changes not F­­­_w

 Jon then went on to describe how he helps his students understand "elevator" problems.  If you are standing on a bathroom scale, and you want to increase your "weight" you can pull on the bottom of the counter and squeeze the scale.  This is the same effect as when the elevator is accelerating upwards.  On the contrary, if you want to lose "weight," you can push on the top of the counter and push you body off the scale.  This same effect occurs when the elevator accelerates downward.

From there, we Jon showed us some fun demos 

1. Have student kneel w/elbows touching knees & hands “praying”.  Put chapstick at tip if fingers.  Then have student place hands behind his/her back. They then need to try to knock over the chapstick by touching their nose to it.  Due to differences in center of mass, girls should be able to do this, while boys usually can't.
2. Have student stand facing the wall, with toes touching the base of the wall.  Have student take 3 steps (toe to back of heel) away from the wall.  Bend at the waist $90^o$ with their forehead touching the wall.  Place a small chair (or other "small" mass) in their hands and tell them to stand up.  Again, boys will struggle,  girls will tend to be successful.
3. Have one student (biggest student) sit all the way back into a chair with his/her feet flat on the floor.  Have a second  student (smallest) stand in front of first student and push into the first student's forehead.  Tell first student, without moving their feet, to stand up.  At the same time, the second student pushes on the forehead of the first, preventing him/her from standing up.
4. Have student stand with right shoulder and outside of right foot touching the wall.  Then tell the student to lift his/her left foot.

Friction Lab

We then moved on to a lab on Friction. We used a friction block and force probe.  The basic procedure was to the block at constant speed with different masses resting on top of the block.  We used the vernier file "Lab 12a Static Kinetic Fric."  A sketch of the graph produced looked basically like this:

The max force represents the static friction force, and when the force is basically horizontal (red line) then the friction force equals the measured force.

To speed things up, each group given different normal force ("zero mass" was mass of block plus 250 g) and needed to get good data (slope of oscillating data was as close to horizontal as possible).  Find the average value of the force using the statistics button.

Unit V Feedback

The Good:

• We felt we were becoming comfortable using computer based equipment
• Continuation of the sequence of showing 3^rd law  (adding non-contact interaction)
• Low tech demo’s/labs

The Bad:

• Modified atwood machine has a lot of physics baggage we’ll need to use as a paradigm

Suggestions:

• When it comes to multiple representations of event
• FBD, motion maps, graphs, equations
• Only let students say verbal description of the event– Carbon dioxide not "See" "Oh" "Two"

Unit VI:

Our introductory/paradigm demo was Jon and Chris tossing a ball back and forth.  Jon then asked questions like: "Once it leaves my hand, where will it go?""Does the ball have a choice as to where it goes after it leaves my hand?"

One thing that come to mind during this demo was the following video from Veritasium.com:
 

What do you notice?
What can you measure?

{at this point, Jon showed us the equipment that we would be using}

{Jon build hold that converts dynamic cart w/ spring into ball launcher}
Here's a rough sketch:

Where the blue shape is the dynamics cart with the spring plunger extended, the silver circle is the ball to be launched, and the brown shape is the holder Jon built out of wood.  He also cut/routed a groove for the ball to roll in on the top of the "shelf."
After being shown equipment What can you manipulate?

{If you don't have time to build this and have students tape it, use videos in loggerpro}

Open logger pro

Click Insert - Movie

Click “expand menu” in bottom right corner

Click scale icon (looks like a ruler)

Make sure you have scale (meter stick) in the movie

Click and trace standard length in screen & define length

Click on track (find name) button and click on specific point on object

Continue clicking on the same spot of the object (vernier advances to next frame)

Jon and Chris then tried to show us the classic Monkey-Blow gun demo using the Pasco equipment:

http://www.pasco.com/physhigh/shoot-the-target.cfm

Since this is quite expensive, Jon explained how he made a "homemade version" of this:

Materials:

Electric conduit (1/2 inch? Metal)

Nail with cone of paper hot glued in

Electromagnet

Wire

12 V power source (3 or 6 V should also work)

Target - Balloon with brass mass inside, washer stretching the opening

            Stuffed animal with metal screw in its head

He attaches the Electromagnet to the ceiling in the back of his room and runs the ingoing and outgoing wires above is ceiling (drop-down I'm guessing) to the front of his room.  He uses the conduit as the blow gun and makes darts by gluing cones of paper to the head of the nail.  Have the two wires run up the side of the conduit and each extent the bare wires beyond the opening of the conduit.  Bend the wires so they touch in the middle of the opening.  As the dart shoots out, it will separate the wires, breaking the connection. Here's his sketch:

 

(click to embiggen)

FIU Modeling Workshop - Day 7

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:

Next he suggested (they didn't find any springs until later in the day) to take the bowling ball and set it on top of a spring, which is itself on the table (you'll bring that part up later).  Ask the students what the spring is doing to the ball (to which they should reply pushing it up)

Then, set the ball on top of soft foam, and again ask what the foam is doing.  Then set it on some firm foam.  Next, set it on top of 2 meter sticks (elevated at each end by some blocks) so that the students can see the meter sticks flex in the middle.  Finally, place the ball on top of table by itself.  In each case, ask what the "base" is doing to the bowling ball.  If they still don't get it, ask what the table was doing to the spring at the beginning of the sequence.

At this point, ask the student to draw a FBD of the ball resting on the table.  At this point, now call the upward force of the table on the ball, the Normal force.  Ask what would happen to this force if the table surface was rotated (incline plane), and lead students to the fact that it is always perpendicular to the surface.

Jon then went on to describe how he uses surgical tubing ("borrowed" from the chem teacher) and student sitting/standing on a homemade hovercraft (here are the directions to make it*)(You can use on office chair if you don’t have hovercraft).  Here's a picture of the setup with an office chair {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)

Take the class into the hallway, and ask for 2 volunteers.  One sits/stands on chair/hovercraft and holds a meterstick at his/her waist.  The second you tell to pull the rubber tubing to a fixed distance.  You tell the person to pull the other victim volunteer such that the distance the tubing is stretched does not change.  Let the carnage begin.  If you want to maintain some sense of safety have the other students line the hallway to help keep the demonstration moving down the hall instead of into doorways and other obstacles.

You can take the sequence to the next level by now asking what would happen if the person seated in the chair/standing on hovercraft were to throw a medicine ball?  (Demonstrate if you have one).  Now ask what would happen if you had a magic contraption that dropped unlimited medicine balls so you could constantly throw them?  Tell them, let's not imagine it. let's do it.  Grab a $CO_2$ fire extinguisher and release the trigger while sitting/standing.  (Jon said he removes any hose/nozzle, and that he worked out a deal with a local supply company to get an old extinguisher, and get ~$10 refills.  He said one full extinguisher will work for all his classes.)  At this point bring the class back inside and have them summarize what all has happened, using FBDs as needed.  Guide the students to the idea of Newton's 3rd Law: If "A" exerts a force on "B" to the "right," then "B" exerts a force on "A" to the "left."

From there, we moved on to individually, complete Unit IV wkst 3

(Jon told us that he doesn't use this sheet as written, but modifies it for his 1^st yt students)

{Has students do the FBD’s but modifies to do progressions in steps, not all at once}
{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:

#4 – group made error on purpose – switching sine & cosine
(Acting as students saying that cos is always the  horizontal component of a vector)

Jon's series of questions: Which leg of the triangle is the longer leg, so which one should be bigger?

• 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?

#8 – Jon – Giancoli has a great problem w/ lawn mower
{Which in looking through my copy looks like #26 in chapter 4}

One question they asked the group (mainly to have some fun at their expense)
If floor is frictionless, how does he push the broom?

At that point someone mentioned this Cartoon over at xkcd
               http://xkcd.com/669/

Next we Whiteboarded sections of Hake “Socratic Pedagogy in the intro phys lab”

Due to time constraints, Jon showed us a trick if we ever need to move things along:
If running short on time – have all students display boards, then ask if anyone has questions.
  Address the questions as needed, and move on.

Here a link to SDI labs as provided by Chris

From there we moved on to another Demo to continue to explain Newtons $3^{rd}$ Law:

Equipment: 2 spring scales & 2 volunteers

Scales attached between the 2 people, 1 person pulls while the other just holds on, then they switch, lastly both pull on the scales.

(If you don't have large spring scales, use 2 bathroom scales/ or vernier force plates)

For bathroom scales (have a "reader" looks over each shoulder & call out values)

Next they set up 2 vernier carts each w/ force sensor attached, on  cart track track
(Jon mentioned that Steiner (sp?) has variations of worksheets in the modeling website, probably under password wall for those that attended the workshop)

(Before you begin, zero the sensors and make sure one has direction flipped, or you won't see both sets of data in the plot)

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

            2^nd Trial - add standard masses to one car, so the collision has uneven mass

            3^rd Trial - One stationary vs one moving

            4^th Trial - One moving fast, the other slow

            5^th Trial - Cars start together and explosion with cart “spring”
{Obviously (?) you could keep going if you feel the need 

Next, they took the sensors off the cars, and attached them at the hooks, and plotted real-time data of the students pulling the sensors apart.

Unit IV: Worksheet 4

(Due to the complexity, Jon has his students first just answer the A/B/C part of the problems and has students whiteboard their answers. Then he has them draw the FBDs, however, they only need to depict the interactions of block A on B and B on A (no other forces yet), and again, they quickly whiteboard their answers.  He then walks them through one or two of the problems, and assigns the rest for homework.  Whiteboard results at the start of the next class)

We again finished the unit we feedback. Chris said they were going to limit the discussion to 15 minutes.

What we liked:

Wkst 3 – we liked FBD  & crunching numbers (we're physics teachers, what do you expect)

Wkst 4 – we also liked how this helped to solidify Newt’s 3^rd law

We liked the progression of demos for 3^rd law

Especially the Laser reflection based on pushing the wall

For the most part, talking about Forces with little math (have yet to bring up $a=\frac{F}{m}$)

What we didn't like:

Would like for this unit to have more lab and less time on complicated worksheets
(Demos are good, but students are watching not doing)
{someone mentioned possibly using force table labs to introduce 2D/trig}

We felt that Worksheet 1 would be too big of a jump our students and would have like to see what Chris did
      to get his kids ready for it.

 A few had concerns that their students would never be able to ever do some of this work

          

Chris also said that for his AP class he has a summer assignment, which is primarily a math review

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?

Hanging mass

Mass of car

Friction: {adjust tilt of track until cart rolls at constant speed}

(pasco hanger approx. applies force to balance friction)

Mass of pulley

Mass of the earth/gravity

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.

Before getting started, we talked about multiple variations to this experiment

• 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!}

Equipment

Attach right angle to cart

Pulley at end of track

Hanger

String

Motion detector

Standard masses