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Motion Shot Photos

May 1, 2017

I plan to get Ss more involved with this from the start next time, and cycling back to it more often. 

Draft of New course Evaluation Survey

April 17, 2017

Its teaching evaluation season… so here’s my idea for a new survey.

An online version of this course would be equally effective.

This class helped me to understand how to learn the material. 

This course was a waste of time.

In this class, I formed meaningful relationships with other students and/or instructors. 

I feel like my instructor cares about me.

This course was one of the best courses I’ve ever taken.

No one would notice if I were absent from class.

This course challenged me to reconsider how I think about certain topics.

Participating in this course makes me feel like being part of something.

I feel isolated and secluded in this class.

I feel a sense of responsibility to the students and instructors in this class.

I am valued as an individual.

If I had to miss class, I would feel like I missed out.

I feel excited about the things I am learning.

Most days I have a good sense of what we are learning and why.

I know what’s expected of me and what I need to do to be successful.

My instructor cares that we learn.

I am given opportunities to learn from my mistakes and failures.

Thoughtful reasoning is valued in this class.

You need to be one of the instructors favorites to do well in this class.

Students are treated with very little respect.

The instructor of this course regularly shows contempt and disdain for students. 

This is the type off course students take to get an easy A.

My instructor seems to put a lot of work and care into the organizing the course.
I wish I could take other classes with this instructor. 
Students wanting to really learn should avoid this instructor. 

I dreaded going to class.

This is the type of class that if you put in a lot of hard work, you will learn a lot.

This course was much better than I expected.

This class was disappointing. 

The grade I expect to get in this class will reflect my level of mastery of the material.

The instructor promoted a competitive atmosphere among the students that was damaging to morale.
Everything we learned in this class was disconnected and random.

I received meaningful feedback on the work I produced.

I am proud of what I’ve accomplished in this class.

I have nothing bad to say about this class.

I have nothing good to say about this class.

Quick Notes: Impulse and Momentum

April 14, 2017

I need to write up a more complete debrief from this week on momentum and impulse stuff, but here are a few things I don’t want to forget:

  1. Spending a lot of time inquiring into (and being puzzled by) force vs. time graphs before mentioning impulse or momentum helped create a “need and interest to know”. We did invention tasks, observations, discussions, and predictions that all together made us really ready to hear about how physicists had invented an idea to simultaneously think about the effect of how much force and how much time. We did a lot of thinking and investigating with jumping off of and landing on to the force plate. I would definitely do landing first, and then jumping. Landing is more intuitive and orients us to what’s going on, and then jumping is what creates the real need to know. How can you jump higher with less force? We then looked at cart collisions with stiff and soft bumpers, to practice measuring impulse two ways in logger pro: Area under curve and Average Force x duration.
  2. With impulse, I also modeled how to make sense of it the number. I wish I had had more time for this, but I helped interpret impulse as how much force I would need to exert for 1 second to get the same effect (or how many seconds I would need to exert a 1N force). think kicking hover pucks vs. pushing them is a good way to show this. It’s important mostly for students to hone in the fact that there are many ways to get the same outcome. 
  3. For impulse, having a class feel continuous (temporally expansive, such that everyday seems connected to now) really helped students make sense of impulse and momentum by drawing on what they know. Without prompting, students were bringing up a lot of good knowledge, including force pairs upon talking about collisions and explosions. It was really easy this year for students to conclude that impulses delivered are equal and opposite, because they really knew how to identify forces pairs and that force pairs must be equal and opposite.
  4. To get toward momentum conservation, we examined explosions carefully,  with 1:1, 2:2, 3:3, 1:2, 2:1, 3:1, 1:3, and 3:2 mass ratios. Two carts were placed on a track with 120 cm of space to move (so 146 cm of actual space, since carts together take up 26). Through this sequence, we observed some, discussed, developed some rules, and then did predictions on how to divide up that 120 cm of space so that after the carts exploded they reach the end of their respective side at the same time. 3:2 was really hard. This discussion gradually folded in conversations about how the velocities compare, how the momenta compare, and how the impulses delivered compare. They did a few more practice scenarios, and then I did some direct instruction on why physicists think of momentum as “commodity” that is transferred, why that implies conservation, and what that means. A little neutrino history was folded in as well.
  5. We then took a look at a few collisions to further talk about momentum transfer and conservation. I did one demo of elastic collision with equal masses just to make the transfer visually compelling, and where story is simple to tell. But then went straight to looking at completely inelastic collisions. Instead of predicting what would happen, we starting observing, and I modeled the story telling process… I told the story two ways: one way was a conservation story (two carts come into collision each brining a certain amount of momentum, they “pool” their momentum, which then must be shared”. The transfer story is more about how much one cart had to lose, and the other to gain in order for that to happen. I did the stories quantitatively, but the emphasis was still on the narrative.
  6. Getting students to tell impulse-momentum stories / momentum transfer stories is a good goal. I had students use the physics classroom collision simulator to first observe (without predictions)… using momentum analysis to tell the two types of momentum stories.  “Combining momenta, and pooling together”” as a conservation story and then also “Individual loss and gain of momentum” as a transfer story. After telling the story (quantitively and narratively), then I’d ask students, “Do you think you could have determined that this would have been the speed before hand? Like predicted it? How would you do that?” Students progressed from telling stories, to anticipating how stories would end. I had students do whatever inelastic collisions they wanted from the start, but next time I would direct them to do a few key ones first, and then let them explore more.
  7. A few groups ended up trying elastic collisions, and found that they couldn’t predict what would happen, even though after watching it, they could tell the momentum story. I hadn’t intended that to happen, but it will be nice to return to this after learning about energy.
  8. In the week, we also did a more momentum-impulse type problem, how much impulse is delivered to a baseball. Can you draw a force vs. time graph that is consistent with this? We played the game of asking students to tell me what information they need, and then we researched on the internet values for baseball mass, pitching and hitting speeds. Students thought they would need mass and speed of bat, so we looked that up to. I would definitely watch this video with students before hand next time…

“I would give anything for students who are…”

April 12, 2017

A student shared this … hope to see yours in the comments.

“I would give anything for students who are…”

However you would complete that sentence—whatever characteristics you most desire to see in the students who walk through your door…

Make it your main goal, day after day, to develop those qualities in your own students.


Impulse: Lesson Planning

April 11, 2017

[Once again, there’s way too much I want to do here, and will need to think about how to scale back]

Constant Force Warm-Up?

Students have  warm-up with a “square” force vs. time pulse (constant over a time interval). Given initial velocity, they have to calculate final velocity using Newton’s Laws and Kinematics.

Edit: I may split groups into two warms up… different width / height pulses with same impulse. Why did these two force scenarios result in same change in velocity?  

Introduce Jump off the Force Sensor:

Orient students to how shape of graph (being constant) force allowed us to assume the acceleration was constant. Tell them I want to show them a force vs. time graph for a real world situation– me jumping off the force sensor. I want to ask them about what they notice about the graph, but before hand I want them to think about what they might expect to see.

I will show them the jump first without the force sensor data (it will be a shallow knee bend and then jump), and ask them to draw a motion diagram and free-body diagram for three stages.

Edit: well Ss work on this, I will encourage  them to do jumps and talk about it. 

  • At Rest on the sensor (before attempting to jump)
  • Jumping but still in Contact with the
  • In the air, before hitting the floor.

Then I will show them the Force vs. Time Graph. Question will be, “What do you notice about the shape of the graph?” Lot’s to notice and talk about here. 

Edit: why did value start where it did? Why did the value go up? Why did the value drop to zero? 

Brief Direct Instruction: Impulsive Forces

Introduce concept of impulsive forces with a few examples, and some features of impulsive forces:

  • Often involve relatively large contact forces between two objects
  • Magnitude of the forces rises and then falls
  • Often occur over short periods of time
  • Maximum force often occurs at maximum compression
  • Shape of the graph is non-constant and can be complicated.

I have a few clicker questions about to apply these ideas to the jump if I feel it’s needed:

  • Where on the graph did I lose contact with the scale?
  • Where on the graph did maximum compression of scale occur?
  • Where on the graph might I have been at my highest point?

Deep Knee Jump Discussion:

Students are going to be asked how the force vs. time graph might be different for a deep knee jump. Once again, show them without the reading. I could ask them to free-hand sketch, which I think, but I will use a clicker question to say, “Which of these does your graph best resemble?).

We will discuss and then observe. Key idea for discussion after is, “How did I jump higher with the deep knee bend even though the maximum force was less?” Key in on the idea of time.

Brief direct instruction to show how force vs. time graph allows us to see two things at once, how much force and for how much time.

Apply Idea of Force vs. Time to Landing on the Scale:

This time I’m going to jump down onto the scale from same height. Once by doing a heal landing with no knee bending, and another by doing a toe landing with knees bending. Students will be asked to whiteboard important features of how the graphs will be similar and different. Students discuss and then we observe.

Direct Instruction:  Representing and Interpreting Impulse

I will either lecture or students will do a close reading of a section on impulse as the area under a curve, followed by some direct instruction to clarify. A big goal I have here is how the impulse takes into account both the of variables that matter (how much force and for how long), but then also scaffold how to interpret the impulse number.

I want to show them that the area under both jumps was the same. That makes sense since the same job had to be accomplished — either way, I fell from same height with same speed, so the job that had to be done was stopping my fall. I will have to guide here strongly, but the idea is that number is how much force would be needed over 1.0 s to get the same result. That another way of stopping me would be to exert a constant force throughout 1.0s = to impulse number in N.

Short Practice Exercise (Hand Calculation):

Students will then have a triangle pulse to calculate the impulse for, to interpret the number, and then draw a different shape graph that was same impulse delivered over half the time.

Short Practice (Logger Pro Calculation):

Students will crash a cart into wall with a stiff bumper and squishy bumper, and calculate impulse delivered to cart. Guiding question will ask them to predict how shape of the force vs. time graphs will be similar / different? [Photogates are not for careful measurement now, but for making sure incoming velocity is same across trials).

What effect to impulse have? Jumping Animals and Marshmallow Blow Guns

From the reading, they talk about how animals that are good jumpers have long legs. Help them relate this to “extending the amount of time”. Just the idea that if you want to deliver a lot of impulse, sometimes it’s easier to extend the time rather than increase the force. But increasing the force is always an option as well.

Show the Marshmallow blow gun. Remind them how with projectile motion we often just assumed that projectiles “started” with some initial velocity. We ignored how they got that initial velocity. Watch I use this blow gun to deliver an impulse to the Marshmallow so it projectiles off with some initial velocity.

Ask students: What could I change about the blow dart gun so that the marshmallow shoots at a higher velocity? Ask why, but also how is consistent with what we’ve learned today about impulse? (Blow harder to increase force, or make a longer tube to increase the time). Let students play for a bit.

Is it possible to use a weak force and a hard force and get the same velocity? How?

Now ask students: What do you think will be different if I deliver the same impulse to a marshmallow that is twice as heavy (two in the gun)…  Let them go observe.

We need to draw out two big ideas here:

There are many different ways to deliver the same impulse, and have same end result (if object is same).

The same impulse delivered to a more massive object, however, results in less change to velocity:

Direct Instruction:


I will either have them do a careful reading or brief lecture on Impulse-Momentum Theorem. Key here is to connect lecture and /or reading to our activities.

Clicker Questions to Practice Applying Idea:

One problem that shows force vs. time graph… ask about change in momentum. Then ask, how much velocity that would translate into for 1.0 kg object, 2.0 kg, 0.5 kg?

One problem that shows a cart rebound off a wall, ask how much impulse was delivered? This will be very similar to quick lab exploration they did, so may do as a demo as well.

Problem-Solving (New Skill in Isolation):

Impulse delivered to a baseball hit off end of the bat?  Draw possible force vs. time graph

Impulse delivered to a passenger colliding into a wall:  Draw force vs. time graph for hitting dash vs. hitting the air bags. How similar / different?

Challenge Problem for Next Time (New Skill Integrated into Broader Skill Set):

Launch marshmallow gun horizontally and mark the landing location. Work backwards to find the impulse delivered!


What Student Say that they Want in Group Members

April 10, 2017

I’ve been experimenting with having surveys where students can tell me one student they would prefer to work with (and why), and anyone they would prefer not to work with (and why, no character attacks), but then also ask them about what makes for ideal people to work with.

This last question has opened a few themes:

A very common one is just wanting to work with people who “care” to learn

  • “Care to learn/understand the material”
  • “I’d like a group that cares about physics, if that makes any sense”
  • “I would prefer to be with the students who really care, because I want really learn the material”
  • “people who aim to understand”

Another is people willing to put in time, effort, and who contribute

  • “I would like to work with people who do not mind staying over, doing the extra problems.”
  • “People who give input or ideas for solving problems and not just waiting for the others to tell them the answers.”
  • “I’d like to be with people who are there to try to do their best. If I was with someone who didn’t want to put in the work and just tried to slide by it would be a bit frustrating for me.”

Pacing  (goes both ways)

  • “I want to work the faster paced group”
  • “I don’t want to work with people who are trying to finish as quickly as possible.”
  • “Similar pace to me — It’s just hard to be patience and not go ahead and finish something on a problem when you know what to do but another person doesn’t.”

Talkative / Outgoing:

  • “People more outgoing than me – I tend to be more reserved at first and it helps me become more involved in discussion if someone else is more open to starting it.  “
  • “I want to work with more outgoing people, who talk and make the work more fun”

Attention to Detail:

  • ” With people who work their problems very neatly on the boards, so that we learn how work through problems clearly.”
  • “People who care about details, instead of rushing to get done”


I think a lot more themes could come out if I asked the right questions… but these are still interesting.

Quantitative Circular Motion Recap

April 7, 2017

We had a pretty awesome day in physics. 1 hour long warm-up. 1 hour long “preparation for future learning” (making predication, analyzing data) and direct instruction. 1 hour of problem-solving.

Long Warm Ups: Applying the Concept of Centripetal Force to Tricky Cases

We spent WAY more time on the warm-ups, then I was anticipating. But it was really needed, and engagement was high so I it took up basically an hour to do 4 clicker questions.

The two we spent the most time on was Car Cresting the Hill, and Roller Coaster Cresting the Top of the loop. Partially it took long because I framed our goal as two fold:

1. To answer the questions on the basis of what we have learned about circular motion the previous class.

2. To decide whether the answer made sense. Students had to vote on the FBD that they thought was correct (A,B,C,D), but also had to vote on a 1-5 scale of how much that answer made sense.

I’m having a hard time remembering what the details of our conversations were, but they touched upon lots of stuff… apparent weight, normal force, object of interest, weight force, velocity vs. force, knowing that the rules say the normal force lessens, vs. figuring out how (what would make) the normal force lessen, trying to connect that to the sensation of… which free body diagram would be correct if you were hitting the bottom of a hill instead of cresting the top.

For the roller coaster, we were pretty split again among many choices, but about 75% of the students picked one that had a central force (with weight down and a second upward force). After brief small group chat and whole class discussion, I re-voiced ideas to navigated us to use what we had learned about circular motion to rule out all but 2 FBDS. Normal and Weight down, or Weight down and an upward force (less than weight). After going to back to small groups to decide which of those were correct, everyone but one person voted weight and normal down. So many people changed their mind to correct answer. Weeks ago, that would have signaled to me we were ready to hear an explanation or two, and then move on. But today was different. I asked the one student, if they felt comfortable telling us why they were sticking with their original choice, and then since so many people had changed their mind, they could tell us what had convinced them to change their mind. The hold out student voiced some good ideas, but the main idea he had was that if the only forces acting on the ball were down forces then the ball would get to the top and fall straight down. I helped make that idea clear, and then truthfully left the classroom while students discussed. I told them I had to go to the bathroom (which was true and urgent, because I had like 4 cups of coffee), and that they should continue the conversation with out me. I came back a few minutes later and they were still passionately discussing the question. (After class the physics major who is undergraduate teaching assistant in my class told me that right when I left, a student who is usually pretty quiet immediately spoke up). Anyway, some of the arguments I heard and others I didn’t, and we gave the holdout student the final say.

Transition to Quantitative:  Preparation for Future Learning and Direction Instruction

The transition to quantitative went smoother than I thought, even though I stream lined it  because of the longer than expected warm up. I reintroduced the pendulum that we had studied before, and asked the question, about what we could change. Students suggested increasing mass, increasing the speed, and strong agreement that would make the force stronger. There was not agreement on what effect changing the length of the string would have… between taking more net force, taking less net force, and taking more net force. I modeled using the pendulum how I actually did these experiments, made groups pin down predictions with reasoning, and then looked at the data– graphs. Students were asked to describe which graph went with which experiment, and patterns in the data, and whether it agreed or disagreed with their conclusions. I thought it might be too abstract to look at the data without actually exploring, but students had enough contexts from our extended discussion to understand the data without actually playing the equipment.

With short time, this led to met doing about 5 minutes at most of direct instruction showing how the patterns from the graphs can be integrated as mv^2/r, and how comparing with Newton’s 2nd Law, this means a = v^2/r.

Ranking Tasking:

Students did a quick job of the ranking tasks. A few students needed guiding questions on some on the ones that were tied.

Problem-Solving: Building the Problem

We did have time to work both problems and to “build” the problems together. I had students tell me what they wanted to me measure and how to predict the tension. I told students the list of must haves. They did a good job of “reasoning” through the problem using representations, and not mindlessly using equations. Honestly, even with thoughtful discussion, good diagramming, they answered the question in about 15 minutes or less. We checked our answer against the demo, and then we were on to the second problem.

We watched the you tube video of car sliding out the exit ramp. I motivated the question of, “So how fast can you go without sliding off?” I asked students to tell me what information they would want to know:

Students said mass of the car, radius of the circle… we had a short debate about whether we needed to know kinetic or static friction. I guided here strongly, by demo-ing. We haven’t studied rolling without slipping specifically, and so I didn’t want to linger here too long, just show the difference between sliding vs. rolling (without any sliding). We talked about needing to know conditions and we talked about ice, wet, and dry. We also talked about assumptions we might need to make:  they suggested we should assume constant speed, and I suggested we should assume a flat surface (even though most are banked).

I gave some canned data rather than have them estimate or research. Everyone did the exit ramp nearest to our highway, where I estimated from google maps it was about 100m radius.

Two groups did icy road conditions: One a 1000 kg car, the other 2000 kg car.

Two groups did wet conditions: One a 1000 kg car, the other a 2000 kg car.

Two groups did dry conditions: 1000 kg / 2000 kg.

Students were asked to predict which in their pair would be able to go at higher speed. Students struggled through this a little more, having to recall things they knew about friction. Some groups struggled with which direction the static friction force points. I used good questioning to help here: “How can you decide which way the forces must point based on what we’ve learned about circular motion during the past 2 days?” “How can you make sense of that answer?” (e.g,. “we need net force toward center of the circle.” and “that makes sense because that force is preventing you from sliding out, not causing you to slide out.”)

Students also needed help with what perspectives to draw things. I could have modeled this, but I ended up just asking each group to make a top view, side view, and a head on view of the car. And to decide which of those three would be useful for representing what kind of information. Now would be a good time to introduce the x and . notations.

Students were pretty surprised to see that the speed didn’t depend on the mass! As we wrapped things up, I had a chance to chat with groups on a one-on-one basis about this. Some groups could explain why pretty well, others needed a bit more direction. It was key to say that heavier one still needed more force, but that is got this greater force by gripping the ground better (normal –> friction).


I’m really happy to NOT be making these problems super difficult in terms of angles and such. Students were really doing problem-solving as a sense-making thing, applying new knowledge to practiced ways of representing and reasoning. I literally have not done an example problem since early February, and it’s never felt like we’ve fallen into the pit of “blindly trying to work the example problem”. Still, students work is sophisticated and not haphazard. High standards are maintained through “must haves” and culture, and most of the high expectations are around representing the work carefully and meaningfully, not in carefully structuring algebra.