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September 17, 2014

Which way is down?

We just finished kinematics, concluding as we usually do with free-fall, which I treat as a very specific case of constant acceleration. This year, I flipped my classroom, and had the students watch a video about free-fall and take notes.  The students reported liking this practice. They can stop the video, and start it again when they have finished taking notes on a particular problem. Students who write slowly have time to listen, understand and then write down what they need to remember. Students who grasp everything the first time you say it can watch the video once and be done. 

The individual who created this particular free-fall video solved several sample problems, including one dropped object and one object thrown vertically upward. In one case, the positive direction was chosen as downward, since the ball was dropped, and all motion was downward.  In the other example, the ball was thrown upward, so up was chosen as positive, and down was thus negative. I really liked the way the presenter emphasized that if down is chosen as the positive direction, then a = g = 9.8 m/s2;  if up is chosen as positive, then the acceleration a = -g = -9.8 m/s2.   I liked it because when I use the letter “g”, I intend it to mean the gravitational field strength or 9.8 m/s2 or 9.8 N/kg.  Always positive. 

But no matter how slowly the students play the video, they always seem to misunderstand. “But Ms. Lietz! The guy on the video said that when the ball is moving down, it’s positive and when it’s moving up it’s negative.” [Their tendency to overuse the word “it” could fill an entire blog entry.] No, sorry. That’s not what he said. But I understand how you came to your interpretation.

I want my students to be flexible, I want them to be able to choose either direction as positive and be able to solve a free-fall problem. Some of them can.  Most of them can’t initially. So we had to have a long conversation about positive and negative and what they mean.  I know we will have many more to come. 

One of my favorite demonstrations to address this particular challenge involves a Vernier motion sensor, Logger Pro and an oversized tennis ball I found at Wal-Mart (roughly the size of a child’s basketball).   I hang the motion detector from the ceiling and drop the ball below it, letting it bounce a few times. All their other experiments have used “away from the motion detector” as positive, and toward as negative. I explain to them that I have set the program to “reverse direction” for the motion detector. That means that away from the detector, which is downward, is now negative. Then we “zero” the motion detector when it is pointed at the floor. This has the effect of making the graph look like it would if the motion detector were on the floor, without having to bounce the ball on the motion detector. Up is positive and down is negative.  Now it’s time for them to predict what the motion graphs will look like for this motion

In my first class, I asked them to predict all three motion graphs at the same time, before dropping the ball.   This led to lots of confusion and all kinds of crazy graphs. So, having the luxury of three more tries, in my next classes I had them predict the position graph first. They had success with this relatively easy task before we moved on to the velocity and acceleration predictions. The velocity predictions were much more accurate once they saw the accurate position graph. And the acceleration graphs are much more accurate as well. I use these graphs to reinforce many concepts.  First, the velocity at the top is zero (we are still talking about one-dimensional motion). We look at the graph of velocity vs. time and see that on the way up, the velocity is positive and decreasing, while on the way down, the velocity of the ball is negative and increasing. I point out that in both of those cases, the acceleration, as evidenced by the slope of the velocity graph, is negative, and thus downward, for the entire trip.    As the ball moves upward, the acceleration is negative, and as it moves downward, the acceleration is negative.   At this point we broke into groups and started working on solving free-fall word problems using the equations of constant acceleration. 

I post annotated images of these graphs on my website for them to refer to later.   Each time a student needs help solving a free-fall problem, we can look at these graphs and remember that the acceleration is down, for the whole trip.    If up is positive, then down is negative. 

This strategy requires that the students are first comfortable with the relationships between the position, velocity and acceleration graphs. When this is true, that understanding can be used to make sense of new concepts.   Nevertheless, the direction of acceleration remains a challenging concept for students, and I am always trying new approaches, new demonstrations.  The ball drop demo, however, is a must.  Many students are helped simply by restricting their coordinate system to “up is positive” and always using that rule.   The weaker students initially need rules to cling to and things that are “always true.”  Others can be flexible. Even in a tracked curriculum, at a school with three levels of first-year physics, the spectrum of abilities is broad.   So my repertoire of demonstrations and other pedagogy must be extensive, and responsive to their needs.   Of course, my patience needs to be great as well, because as soon as I finished my fourth time through this demonstration in one day, some student got a practice problem wrong, and exclaimed,  “But I thought the acceleration was positive on the way down!  That’s what the guy said in the video.” 

September 7, 2014

A Curse and a Blessing

This year is my 25th year teaching physics, and it is the first year I am not teaching AP Physics C.  At first I was very disappointed because I love that course. I love teaching the best and the brightest in the school.  Of course there are some challenges to teaching Physics C, not the least of which is that I have to get exhausted second semester seniors to understand electricity and magnetism, including the Biot-Savart Law (think Coulomb’s Law for magnetism). 

But this year, the powers that be decided someone else should teach AP Physics C, purportedly so that I can focus my full attention on our new AP Physics 1 course.   (Did I mention I’ve taught Physics C for 24 years?) My full attention. That means I have the opposite problem of most teachers out there who teach three, four or five preps: I have one prep. I teach four classes of AP Physics 1. (Yes, I’m blessed to teach only four classes.) At first I thought this was a curse. Sometimes I still do. I had a hard time last year with three Honors and one AP C. By the third time I solved the same projectile motion problems as examples for the Honors classes, or the third time I crashed those carts together to demonstrate Newton’s third law, I could barely remember if I had or had not remembered to remind them about the quiz tomorrow. Thank goodness for (see my prior blog post “Communicating with Students”).  Now I have four of the same, not three. By the fourth time I review the answers to the same worksheet, I think about getting a new job.

But I love my job. As you can probably tell already, it’s a very good job with much better teaching conditions than most teachers I have met and many more I haven't. So I remind myself that rock stars sing the same songs show after show after show, night after night. Broadway stars perform the same scenes day after day for years if the play has a good run. So I buckle down and figure how not to bore myself this year. The first thing I did was re-imagine how we review homework and quizzes. I used the “Stacks of Kinematics Curves” worksheet from the Modeling Curriculum out of ASU, and I always need to review a few of the more challenging questions with them. But not everyone needs the help.  So they sit there bored while I explain it to the other students. Instead, I put the answers on-line, put the students in groups and sent them to the lab tables to discuss the homework for 8 minutes. The students who got all the answers correct the first time explained them to their peers who were more confused. I circulated answering questions. Students who would be intimidated asking a question of the whole class were brave enough to ask the three other people at their table.  If no one at the table understood it, I was there to help. I thought it went well, and the students seemed to like it. And I think everyone, including me, was less bored.

I’m also making a much more concerted effort to “flip” my classroom on a regular basis. I believe that students should be interacting with each other and with me while they are in the room. They should not be sitting silently next to each other taking notes. However, I take time each year in the middle of the kinematics unit, just after we finish graphs of motion to derive the “big three”: the equations of constant acceleration motion.  I derive them from the graphs of motion, from the slope of the velocity vs. time graph, and the area under the velocity vs. time graph. I didn’t relish doing that four times in one day, so I decided not to.  Instead, I took the time to make a five-minute video. The students were required to watch the video and take notes on a page in their kinematics packet. All but two or three students in each class did this, and came prepared the next day. We spent the day solving kinematics problems, first as a class, and then in groups of three or four at the lab tables. The students got to work at their own pace, and they were working with others who could help them if they got stuck. I liked the way it went, and I plan to do it again. I’m still working on the details of flipping lessons, such as holding them accountable and what to do when students don’t prepare adequately. I am grateful for websites like and all the great videos by Dan Fullerton. He does a good job presenting the content clearly, and highlights all the points I would highlight if I had made the video. But since he has done such a good job, I don’t have to. 

This is just the beginning of the year, and just two of the changes I have made. I have been given this year the mixed curse and blessing of only one prep. I choose to focus on the blessing aspects, and have fun learning new things.  

*For those of you who want help flipping your Physics C course, I recommend Viren’s Videos.    
**More resources can be found at my Teacher Training site that I created for the summer institutes I present each year. 

August 30, 2014

"How do I know what I know?"

I had the great pleasure this summer to hear Dr. Eugenia Etkina speak at the AAPT meeting in Minneapolis, Minnesota.   Dr. Etkina is a physics professor at Rutgers University, the creator of the I.S.L.E. (Investigative Science Learning Environment) curriculum and is the author of a recently released textbook based on that curriculum.  She was the recipient of the Millikan Medal and her hour-long talk is outstanding.  Her talk is now available through AAPT on the University of Minnesota web site.  You can find her talk here.

Quotes/ideas from the talk:

  • What you you want your students to take away from your course?
  • How do we know what we know?
  • The process of constructing new ideas is as important as the application of those ideas.
  • Experiments play three distinct roles: observation, testing and application.
  • Representations are reasoning tools.
  • Reading the textbook comes after you construct the ideas.
  • If you want to flip the classroom, let students observe things at home through videos, then construct ideas together in the classroom, and only then read the textbook.
  • Don't be afraid to have crazy ideas and make mistakes.
  • Get used to working with others.

You can also find other highlights of the AAPT Summer Meeting on the AAPT web site at this link.

Dr. Etkina's resources for implementing her curriculum can be found at

The Physics and Astronomy Education Research (PAER) group at Rutgers University can be found at

August 22, 2014

Dear Ms. Lietz

At the beginning of every year, I write my students a letter so they can get to know me a little better.  Nothing too personal: where I went to high school and college, how many brothers and sisters I have, hobbies, music I like, etc.  And then I request the same favor of them.   I thought I would let you know a little bit about the amazing students who grace me with their presence in my classroom on a daily basis. their own words....
  • I was born in Deagu, South Korea.
  • I have lived in Morton Grove all my life. 
  • I've gone, and still go, to Polish school every Saturday. 
  • I was born in Adis Ababa, Ethiopia.
  • I was born in the Phillipines and moved to the US at around the age of five. 
  • Over this past summer I went to Pakistan and worked as sort of a farmhand at my uncle's farm. 
  • My mom was a drafting engineer in Iraq, which was her dream job. 
  • I am Filipino Irish and 16 years old.

  • I started to memorize the Qur'an which is the Islam version of the Bible.  I am still not done, but I do not have a lot left.  
  • Two of my biggest accomplishments in my life thus far is becoming a Bar Mitzvah and also earning my ham radio license. 
  • I can say that Christianity is a big part of MY life and also my family's.

  • I'm addicted to cooking shows.
  • I also enjoy going to the beach and hanging out with friends. 
  • You can pretty much describe me as Tomboy mixed within a Girly-Girl. 
  • My hobbies include dancing and singing which are the two things I love doing whenever I can.
  • Paris is the top of my destination list.
  • I participate in "Electric Shabbat" at my synagogue once a month, where we take traditional Jewish prayers and turn them into rock and roll. 
  • I have a cockatil [sic] bird, a few goldfish, and two huge Rhodesian Ridgeback dogs.
  • There was a time we won fifty goldfish at a carnival, but they all eventually died.  
  • Taking pictures is something I have always enjoyed. 
  • I went to Istanbul after I performed Pilgrimage with my mom.  
  • I like the "Outliers" because it proves talent is not just something you're born with, it's something you can have through practicing and opportunities. 
  • Some after school activities I do are cheerleading and Serbian club.
  • Even though liked soccor [sic], my true pashin [sic] is Basketball. 
  • One of the more serious things about me is that I have a disease called Lupus. 
  • I am on the Soccer and Gymnastics team here at Niles West.
  • I happened to watch "Chucky" when I was in first this day I'm scared of dolls and stay away from American Girl dolls specifically.  

  • I enjoy researching, and previously I had conducted experiments which incorporate taking antioxidants from pomegranates and applying them to HeLa cells to study the mechanism of antioxidants and free radicals and correlate it to cancer growth. 
  • I am now in my third year of fashion, taking Fashion Workshop as a third elective, behind German and band. 
  • I took part in the SSEP program.  I got a chance to design for NASA to fly in space. 
  • When I entered sophomore year, I started donating and raising money for the charity "Relay for Life."

  • I'm warning you ahead of time, I struggle with sciences and get frustrated easily, but that doesn't mean I don't try hard. 
  • I've always thought of myself as more of an "English and social studies person" than a "math and science person"...
  • I am also described as disorganized which I want to fix this year. 
  • I am a strong advocate of our nation's military and am going to join the US Marine Corp for two years sometime after high school-college. 
  • I actually want to work in organizations such as the United Nations and help contribute my service to somehow make the world a better place. 
  • My dream is to attend Berkeley University and major in nutrition. 
  • I took AP Physics because I want to become an engineer when I grow up. 
  • I'm a little torn between making programs and stuff that model diseases and help the medical community, and between making video games. 
  • It's nerve wracking thinking about what the future holds. 
And that's just the start.  I haven't even finished reading all of the letters yet.   They are such a mix of the mundane and the extraordinary, sometimes within the same letter.  I find it helpful during difficult times to know that there is a gifted dancer inside that young man who can't seem to figure out whether he should use sine or cosine for the horizontal component of the force.   They are not all "rock stars" in my class, but they are all unique individuals, with varied gifts and passions.  And I am blessed to know them all.

August 14, 2014


Each year I start off with a mathematical modeling unit involving the classic pendulum lab: "What factors affect the period of a pendulum?"  It is a simple system we can use to take measurements and graph data, and use the data to come up with an equation. And each year we start with brainstorming session. I ask the students to come up with ideas about which factors affect the period of the pendulum. They provide the standard fare: "weight", "length," "starting height," "wind resistance," "gravity," "starting force," etc. We pare it down with a discussion of what we can measure and what we can control. Wind resistance is eliminated: we can't vary that in a regular way.  Gravity is eliminated: field trip to the moon is not in the budget. "Weight" becomes "mass", and "starting height" and "starting force" both are subsumed under the "angle" category.  

This year, we had a new entry: "inertia." Hmmm. So it's the second day with these bright juniors, and I don't want to squash their feelings right away, so I entertain all ideas.  But this one needs clarification. Clearly this student knows some "physics lingo." So I queried,"What do you mean when you say 'inertia?'" I say it with sincere interest, emphasis on "what do you mean."  The student stumbled a little bit before continuing, "Well, you know, when you start it swinging, and it goes back and forth for awhile, decreasing slowly each time until it comes to a stop? Inertia." Oh, right "inertia" - almost exactly the opposite of what physicists mean. So at that point, I'm forced to disappoint the student, and very briefly explain what physicists mean when we use the word "inertia" and how we will discuss that later. And what the student means is something else, which we are going to ignore here by not letting the pendulum swing for too much time.

Or maybe it's more subtle than that. Part of the definition of inertia is the tendency of objects to remain at rest.  So the pendulum slowing down and stopping: it's tending to go back to being at rest.  That's inertia, right? Alas, no, it is not.

I am thus reminded that these students not only do not come to me as blank slates, but they come chock full of misconceptions and partially formed ideas, heaped on them by movies, TV, news and by well-meaning, poorly-trained, over-worked (and, no doubt, intelligent) middle school science teachers.  So many physics words have entered the mainstream that I can't keep track of them any more. "She's a real force to be reckoned with." "The stock market lost momentum today." "You shouldn't make such a quantum leap in your reasoning." And that's just physics words appropriated by other disciplines. What about the mistakes people make when trying to apply the physics correctly? As I say to my students, "Don't get me started." However these misconceptions are planted, I need to confront these them head on, or they won't go away. I am reminded to not use words they don't know until they have a concept that needs a word. Concept first, name later. Otherwise we are just teaching vocabulary…with math. And in AP Physics 1 (formerly known as Honors Physics), we have LOTS of math. Especially the most frightening of math: algebra!

If I don't want my physics class to be reduced to vocabulary plus math, I have to strive daily for the ever elusive "deep conceptual understanding." I have to search out those misunderstandings. I have to stop myself from dismissing a student's "silly answer" and really listen while they explain what they are thinking. And then (this is the tough part) I have to devise a way to show them a new way of understanding. A way that will stick long beyond the unit test, all the way to the final exam…and maybe even until they get to college.  Here's where it gets really fun: there are 24 students in the room.  [Yes, I'm spoiled that way.  Small classes.]  And they each have their own preconceptions. And in 42 minutes they leave, and 24 more walk in the room with a whole new set of preconceptions.

Fortunately, I know most of these preconceptions*, and I usually have a plan for those.  But every so often there's a new one.  Like inertia.  And I have to really think on my feet.  That's the challenge despite teaching the same thing every year: someone, some day not too far in the future will walk into my classroom and reveal a way of thinking about something that I haven't encountered yet.   I get to meet them where they are, and walk them over to a new way of thinking.   I get to use toys and demonstrations and labs and ranking tasks and humor and compassion and, for the really bright ones, I get to use algebra.  That's what we in the business call "phun."  

*Thanks to all the other physics teachers and students who have taught me about these misconceptions during my career, and to a great book by Arnold Arons.  And of course, to my dad.  

August 4, 2014

Communicating with Students

The new school year is about to begin and it is time to set up my web page and get ready for a new group of students. I post my class schedules, links to videos, handouts, solutions to homework and many other resources for students on this site. But the web page is jut one method of communicating with students.

A little over a year ago, a colleague brought my attention to a web service that allows me to send text messages to all my students. That service can be found at I've used it regularly ever since and I love it.  I've long had the capability of sending email to groups of students, but that method of communication was not as effective as I would like it to be for several reasons, primarily that students don't check their email nearly as frequently as I would like them to. But they check their text messages as soon as they arrive. I know because I have seen it happen: I've sent a message after school and, two minutes later, a student in the room pulled out his phone, saw the message and said "Thanks, Ms. Lietz." is a service that allows students (and parents) to enter their phone numbers on a web site and sign up for a very specific class. Some of the benefits of this service are:

  • I never see the student/parent phone numbers.
  • Students don't see other students' phone numbers. 
  • I don't have to give students my phone number.
  • It is a one-way service: students cannot respond to messages.
  • I can message as few as three students or as many as all of my students in all of my classes, all with one message.
  • There is a record of my messages on the website.
  • If a student doesn't have a text message service, they can receive the messages via email.
  • There is an app for my mobile phone so I can send messages from my phone.
  • I can schedule messages in advance so I don't forget to send them.

What have I used the service for? Like a tweet, the character limit is 140, so I use it mostly for short messages.

  • I can remind students about homework that is due, or an upcoming assessment (but I usually only do that if I forgot during class).
  • I can send them a text in the morning reminding them we are meeting in the computer lab.
  • I can remind them to bring in their money for a field trip.
  • I can text them during the field trip to remind them when and where to meet the bus. 
  • I can send them a link to a good video about the current lesson.   
  • I can let them know I sent a lengthy email that they should check before class meets again. 
Our school cell phone policy allows students to use their phones during passing periods and lunch, but only with teacher permission during class. And their phones are supposed to be off when they are not using them. However, I try to time the messages during passing periods if I send them during school hours, and most of my messages are sent during after school or evening hours (occasionally at 7 A.M.). I may send two messages in one day, and then no other messages for another week: I try to save messages for important announcements, reminders or things I forgot to say in class.  

Some colleagues have shared that they think this is enabling students, and perhaps it is. The homework schedule is posted on-line, so I don't text them each night to remind them about that. I prefer to think of it as communicating with them in a mode they prefer. Communication with them was much more effective last year, and I plan to continue to use the service this year. 

If you wish for students to be able to send you text messages, I recommend a Google Voice account.  I post that number on my web page, download the Google Voice app to my phone and communicate one-on-one with them as needed. Since we are a Google Apps district, the account is free. All the messages are recorded for my security and for the student's security. I haven't had this problem yet, but if I ever receive an inappropriate text message from a student, I have record of it in the cloud. I set up the Google Voice account so messages go to my Google Mail account at school. That way, I can respond to them in my mail program, and they get a text message. And I never have to give out my personal cell phone number to them. If they get sick on a ride at Great America during our field trip, they can reach me via Google Voice. And of course, if they text me after 10 pm, I return the "favor" by texting them at 5 am when I get up.  

Effective communication with students is essential for their learning, and these and other web-based tools can make that communication simpler, both for teachers and for students. If you have any you find effective, I'd enjoy hearing about them.