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.