Book Review (?): Force and Motion by Jason Zimba

I happened to pick up a year ago while in a used book store called, “Force + Motion: An Illustrated Guide to Newton’s Laws” by Jason Zimba. Although I wouldn’t necessarily recommend it as a introductory textbook, it has some real nice gems which could certainly be put to good use. Here are a few things that make it a worthwhile addition to your collection as a teacher:

Discussions of Ontology

In Chapter 10, “The Concept of Force”, one of the first sections in the chapter is called, “Force is not Havable”. Here and else where, the authors discusses the ontology of force partly by examining examples from english language. In this section he analyzes examples that emphasize how forces always involve a pusher/pushee (e.g., “I push the wall.”). In other sections, his worked examples (instead of being problems to solve) are lyrics and quotes that use the word force. The problem as presented to the reader is to explain how the use of the word differs from the physics usage and to rewrite the line to make it more consistent with the physicist’s conception. One example is, “I helped her of a Jam, I guess,/ But I used a little too much Force.” from Bob Dylan’s Tangled up and Blue. His solution to problem begins, “The problem with Dylan’s use of the word force is that he makes it sound as though force is a substance that can be doled out–you can use too much, too little–like garlic…”

It’s the kind of things that might be the right kind of task for the future physics teachers in our program.

Attention to Learner Difficulties

In discussing force diagrams, he is very careful to spell out things about Forces and diagrams that students struggle with. For example, he has sections titled:

“A Force Diagram Focuses on a Single Target”–in many texts this goes unsaid or said said in a passing way. There’s a whole section devoted to this idea.

“Forces can Turn On and Off”, in which the authors writes, “Forces are evanescent things. They are not like material objects. They appear and disappear all the time… When you and I are shaking hands… once we let go of each other’s hands, both of these forces simply vanish…”

“A Force Diagram Illustrates a Single Instant in Time…” This idea has become a big emphasis in my own teaching of force.

In general, what I appreciate about the text is that it’s not just, “Here’s the correct physics understanding of these concepts” Instead, the text seems to be focused on, “Here are ways of thinking about these physics concepts” Many of those “ways of thinking” seem informed by ways that learners especially need.

Attention to Intuition and Argument

In some of worked problems about force, the author actually introduces incorrect force diagrams (e.g., force in direction of motion), accompanied by student dialogues about them (e.g., “the force keeps the bullet going across the field”, arguments against them (e.g., The rifle is not longer touching the bullet”, and rebuttals “But if there’s not force, what keeps the bullet moving?”. He ends, not with disdain for misconceptions, but with a tacit love that recognizes how confusion about the right issues is at the heart or learning: “Now we reach the heart of the matter. Bob’s instinct is that something must keep the bullet moving across the field. I’d that’s a perfectly reasonable instinct. Bob’s mistake is to seize on force as the sort of thing that keeps the bullet going… ” He goes onto the introduce, but not settle, the struggles and thoughts of Newton in his attempt to address this issue with the concept of inertia.

In making this progression, he is keeping our attention to definitions, argument, intuition, and joy of recognizing (even if not resolving) contradiction.

Refining Learner’s Intuition to Find “Seed of Truth”

In Chapter 12, the aithors introduces a section called, “The weaker link between Force and Velocity”. So often we can focus on, “What’s correct” or “What’s wrong”, but I think this author does a nice job of returning to arguments, and refining them.  The idea the authors returns to here is the common idea that force and velocity are linked. I’d never thought about it this way, but here’s what the authors has to say about the misconception regarding the connection between force and velocity.

“What about the link between force and velocity? Is there a link at all? The answer is that overtime there’s a link. If you apply a steady force Fnet to an object for a long enough time, the velocity vector v will eventually turn itself around more and more to a point along Fnet… However, at any fixed instant, there is no obvious relationship between the Fnet and v vectors… Students often want their force diagrams to show them something about how their target is moving at the moment of time in question. But force diagrams can’t do that. Indeed, because Fnet points along the acceleration vector rather than the velocity vector, it would be better to say that the force diagram shows you something about how the target is about to move.”

He goes on to discuss the power that this subtle idea gives: The power to make predictions, not just descriptions. What’s happening now, actually tells you about the (near) future.

Awareness that Mathematics is a Language–the Case of Rearranging Algebra

He has a section called, “Rearranging Newton’s Second Law,” in which he introduces Fnet = ma  as a rearrangement of  a = 1/m Fnet. In doing so, the authors talks about how Newton was in the business of observing accelerations (of planets) and trying to figure out the forces causing them; and so for him Fnet=ma  made sense because acceleration was the input while force was the output of his investigations. He does a nice job in other places of discussing this as the two major kinds of problems in physics–what can motion tell you about forces underlying some system vs given some known forces, what can we say about what some motion will be.

Other notable things about this book are it’s strong focus on vectors, graphs, reasoning, and history of science. In general, the text has some nice insights into student thinking; and when he discusses difficulties and mistakes students tend to make, he is not disparaging. Instead, he tries to understand why students would say, think, or do those things, and it makes for a pleasurable read.

I’m sure there’s things “not to like about the text,” but that’s the game I’m playing with this book review.

If you’ve read this (or get around to), let me know what you think in the comments.



Learning about the Moon this Semester (Rambling notes for me, but you can read them if you want)

Late Jan, February, and Early March: 

~2 months of observations, light discussion, and moon journaling during inquiry units on other topics. The 1st month was done without much structure, except bi-weekly self and peer evaluations assessing mostly whether it’s getting done. 2nd month had more explicit focus on measuring angle moon and sun (after instruction on some methods of doing this), and still bi-weekly peer evaluations but evaluating more explicit expectations about what should be in an entry. During both months, we made in-class observations whenever weather and phase were amenable. We also discussed our moon observations and thoughts on the moon about 15-20 minutes per week, sometimes spilling over more. There was one day where I think we spent 1.5 hours talking about the moon. Early discussions often revolved around, ‘When did we last see the moon? When do we think you will see it again?”, “How come we couldn’t see the moon last night?”, “Why (in the world) could we see the moon out during the day?” “Where do we think we’ll see the moon and sun if we come out at the same time tomorrow?” “When was the last time in our journals where the moon looked like this?”, “Does everybody see the same moon the same way around the globe?”, “Why does the moon sometimes appear orange?”

When I do this again, I will more deliberately introduce and give practice with compasses and coordinating that with looking at maps of our school and their homes.

Week One of Focused Moon Inquiry

Day One: Initial Moon Ideas with Crumpled Paper Toss

Everyone was asked to spend 5-10 minutes writing about why they thought the moon went through its phases. Everyone had to use words and diagrams. Everyone knew they were going to crumple up their writing and toss it in the middle of the room, and then go get one that was no their own.

With elbow partners, students read and discussed the ideas and diagrams in the paper they found, and had to prepare a whiteboard to share what they had found about other’s ideas. Here is a smattering of the ideas

  • The phases of the moon depend upon a little bit of everything: weather, temperature, the seasons, etc.
  • The phases of the moon are the result of the earth’s shadow passing over the moon as the moon goes around the earth
  • The phases of the moon are caused by the moon spinning (around its own axis), 
  • The phases of the moon are the result of a “blow out effect”, whereby when the moon is close to the sun, the light from the sun overwhelms our view of parts of the moon (like how too strong a flash can “obscure” details in a photograph).
  • The phases of the moon are related to the various orbits and rotations of moon, earth, and sun, 

This served the purpose of getting ideas on the table, focused us on the role of trying to understand other people’s ideas, and introduced us to the real challenges of writing about your ideas so that others can understand. This whole unit builds toward writing a moon paper, using structures from “They Say, I Say…” by Graff & Berkenstein, so students have also had reading assignments from the book. 

Day Two: Creating a Community Moon Calendar

We spent most of the day, taking data from our individual journals and putting them onto large calendars I had created on the whiteboards around the room. I’ve tried in the past of “structuring this” in various ways, but I found it went well this time to let students just go up and put something on the board free-for-all style. Not one at a time, just mob style. The only structure I gave was, before hand, suggesting that we all share convention of whether shading in a diagram will show “what’s lit” or “what’s not lit” of the moon. Otherwise it gets confusing. I also encouraged students to check if someone else in class had a similar observation before putting anything up and encourage students who hadn’t gotten up to do so. I also let them chat off-task if they wanted.

It was a low pressure situation with a relaxed tempo and vibe. Many groups were up and adding things to the calendar, discussing. Other were comparing notes from their journals at their desks. Some were hanging back. A previous me would have thought ill of the laxadasical flow and pace, which included a real lack of structure and even permitted off-task talk. Someone watching my class could have easily just been confused as to why I was just letting students wander around, some on task, some off task. It could seem to someone else that it took us a lot of time to do this, and someone could have been wondering if this could be done more efficiently. I think the feel and pace was near perfect. [Side Note: In general, my feeling, thoughts, and even response concerning off-task talk has changed dramatically over the last 3 years.]

Afterwards, we started looking for patterns. Patterns we discussed were ideas related to waxing and waning about how it seems to take 28-29 days to repeat. Other patterns focused on what side of the moon was lit and what time of the day. Next time I want to scaffold this a little bit towards “proposing possibilities” language such as “I’m noticing that, I’m wondering if…” One reason is that some patterns students will suggest will be “correct” (from scientist’s perspective) and others will not. I don’t want to be put in the position (now) of having to be the arbiter of that. Second, I want students to feel OK in proposing possibilities. Third, I want every student to be in the position of deciding whether or not they understand the pattern being proposed, whether or not they agree that pattern might be there. 

Day Three:  Analyzing Writing Moves (and Modeling a Specific Moon Day)

Students had just submitted their first writing assignment the previous night. I took an example from one student who had decided to write about the blowout theory–what the idea was and why they had come to believe that the blowout theory could not be an explanation for the moon phases. The assignment had to been to write about one idea from class and then respond to it–either agree and give reasons or disagree and give reasons.

In class, students were given the excerpt and the prompted to:

  • (A) Highlight phrases within the text that signal to the reader whether they author is discussing what “Others Say” about the moon or what “They say” about the moon. 
  • (B) Highlight phrases within the text that signal to the reader that an idea is about to be clarified, elaborated, or compare/contrasted. 
  • (C) Highlight any other important phrases or words within the text that you think standout. Be ready to explain why you chose a phrase, and what purpose you think that phrase serves in helping the reader understand the text.

Here is the (snippet of) student writing that was analyzed and discussed:

“One observer believes that the Moon’s phases are in direct correlation to the specific distance of the Moon from the Sun as it travels in an orbital path around the Earth. They say that when the Moon reaches its closest possible orbital position next to the Sun, the bright sunlight overpowers the lesser light of the Moon, thereby making the Moon virtually invisible to our eyes. Then, as the Moon continues to travel in its orbital path around the Earth – it is simultaneously changing in its distance from the Sun – and, that is what causes us to observe incremental changes in the phases of the Moon. This theory seems to imply that the further away the Moon moves from the Sun, we are then able to see a larger area of the Moon’s surface. 


Personally, I disagree with the first observer if by their explanation they are implying that the Moon is a lesser source of light than the Sun. Based upon that premise, we wouldn’t be able to observe different phases of the Moon’s surface. Instead – depending upon how far the Moon is away from the Sun along its orbital path around Earth – we would only see varying intensities in brightness of the light upon the entire surface of the Moon itself. Thus, I say the Moon merely reflects the light which originates from the Sun.”


After students worked in groups to read and discuss, we put the text under the document camera, and students suggested lines to highlight and gave reasons. 

After the writing discussion, we decided to pick a day/time that we had all made the same moon observation and try to explain/model what was going. We chose a day from our moon calendar where we had made an in-class observation–that way we knew everyone had seen the same thing and had a moon journal entry. The observation we picked was a crescent moon seen to the right of the sun around noon time. Every group had available to them for modeling– a globe, a styrofoam ball, a light bulb; whiteboard with markers; they also had a envelope filled with various two-dimensional laminated cutouts of suns, moons, day-time skies, night-time skies, grass, people, and even words like, “Noon”, “East”, “Up”, “Sunrise”, “Midnight”, “North”, etc. Students worked in groups trying to create a model that would help show them what was happening that day to create a crescent moon seen to the right of the sun. I circulated around as students engaged in the task, but we didn’t have time that day to share out anything. Students didn’t necessarily stick to the task of the crescent (which was fine). Many students were engaged in modeling the moon’s phases more broadly. Here are things I noted that day:

– One group had decided that the moon could not orbit around the equator, because it would seem that there would never be a full moon. They were excitedly toying with the possibility that the moon went over the pole’s instead.

– One group was becoming increasingly confident with the shadow theory.

– One group was becoming increasingly disenchanted with the shadow theory

It’s not true that the groups were so homogenous, perhaps it’s better to say that these three things were happening. There was a loose correlation with groups. But I know there was one anti-shadow person in the group that was swaying toward the shadow theory. And I know that two students in particular were driving the disenchantment with the shadow theory. 

I’ll write later about what happened the following week. I actually had to miss class the following Monday and so students had to run class without me. 

Here’s quick outline for me to remember:

Monday: Student-led Class–explaining the shadow theory in depth; and introducing objection’s. [Bubble Popper vs Brick Builders]

Wednesday: Building Foothold Ideas: “What We agree on, What we don’t agree on, What questions we still have”; Shadow Theory Revisited

Friday: Olaf’s Cousin who lives in a Rocket Ship; and Spinny Chair Modelling

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